In depth (chilled out!) model discussion

[Paul]

To cater for those who prefer a slower pace, more in depth discussion around the models, we've decided to setup this new thread. So if the drama and excitement of the main model thread isn't quite your thing, then please feel free to post into this thread. 

You're also welcome to cross-post - so if you've made a longer post in the model thread, you can copy it into here, and vice-versa. 

[johnholmes]

john h for net weather 6 feb 17.doc

done in great haste but hope to do a more carefully thought out look at 72 h plus tomorrow morning, maybe a longer look as well.

Edited February 6, 2017 by johnholmes

[Singularity]

 

9 minutes ago, Tamara said:

Good analysis and perspective earlier from nick s about the Scandinavian High and energy equation involved in any retrogression signal

I think at this stage there are a few things to state (and in some cases re-emphasise)

1)  There is a two day lag updating-work-in-progress continuing with the Global Synoptic Dynamical mode (GSDM) which provide us with a highly useful and NWP-pro-active guidance tool to asses how much tropical (MJO) and extra tropical (frictional and mountain torques) will produce a combined amplification wind-flow signal to impact the tropospheric NWP patterns and also poleward propagating mechanisms to further destabilise the polar vortex. 

The timelines involved in this means that the full effects of the tropical signal in the Pacific will be working their way polewards from tropics to mid and higher latitudes over a period of some days at a time. The signals can be evaluated in advance as to their likely impact on NWP - but full impact assessment is very a much a case of documenting progress daily through AAM total budgets as reflected by the Global Wind Oscillation. In this sense the MJO forecasts are not the whole story - it is the GWO that supplies the full wind signal and determine the hemispheric pattern and degree of meridionality of the jet stream

We must therefore, very importantly factor this in when assessing NWP  - and one highly good reason amongst others to avoid knee jerk responses to operational (especially) but also some ensemble date suites. This applies tonight as much as the last 10 days which (as far as I am concerned) is when this journey towards a cold spell began amidst suggested long term cyclogenesis. This rationale will also continue to apply, reflecting a highly dynamic evolution with a complexity of timings that imply whatever individual operational roll-outs *might* show, it *should* still be an exciting one too.

2) Next up, the GSDM aspect has to be considered in tandem with stratospheric developments and the movements of the vortex within the polar field. The GSDM is contributory to this in terms of poleward rossby wave eddies in evidence set to further perturb the vortex, but the maximum damage potential in the form of  cold air advection through strong amplification is made possible by the most 'favourable' destabilisation mode within the vortex itself. There is increasing agreement for the vortex to become resident over Siberia, but there is not (yet) agreement on whether this arises through split or displacement.

Clearly displacement mode involves momentum transport across the pole and, as nick rightly says, this process comes with greater energy (temporarily) exerted on the Scandinavian block. One more reason to not be surprised by the NWP volatility and differences evident between models and intra day modelling suites.

Clearly current NWP highlights these energy imbalances - but it is vital that they are captured merely as snapshots in time and neither represent the inevitable, nor are they, as already stressed, a complete picture by any means

With that in mind, lets look at what we know, which includes todays GSDM updates (remember the two day lag)

As suggested in yesterdays post update, global atmospheric angular momentum tendency was set to respond sharply. Todays lag to the 4th shows it has rocketed upwards in continued response to the upstream tropical (MJO) signal coming into the Pacific - destined eastwards

But as stated already, the tropical 'engine catalyst' for the amplification signal isn't the complete story. Feedback processes for poleward propagation of amplifying poleward eddies from the tropics to extra tropical mid and higher latitudes occurs over timeline periods. NWP is constantly calculating this evolving process and adjusting. When it involves complex amplification and strong blocking processes such as we currently experience - expect uncertainty and drop in performance - but don't be sad and fitful over less palatable solutions which may be either transitory graemlins or phantom model weather watching demons 

The Global Wind Oscillation (two day lag once more) has continued etching up in amplitude through Phase 4 (again as suggested yesterday)  as it starts to respond to the rapid rise in angular momentum tendency. 

 

This has implications for global torques moving forward, and the net outcome of amplification in the atmospheric circulation budget will determine the tropospheric response available for cold air advection moving ahead. That is also beyond the easterly.

The movements within the polar field will clearly either offset or augment this potential depending on displacement or split mechanisms - but make no mistake, a harmonious tropical and extra tropical wind-flow signal cuing up large amplification forcing dovetailing with favourable stratospheric developments could deliver an icing to top the initial Scandinavian cake.

Don't fret over any suggested pause heading into next week. We cannot yet know all the answers. We can only look around corners available. But the GSDM offers an additional forward insight to where NWP may head.

Atmospheric circulation and stratospheric caveats aside, this has a long way to go yet and the nice little easterly could conceivably be a precursor to a bigger reload from the arctic to round off official winter 2017.

 

 

If any post deserves to kick this thread off, it's this one 

Great idea Paul, I'd have loved this when I was allowed to go into fine details even at the longer range 

[johnholmes]

A quick look at what the models are suggesting for the start of the cold spell

net wx tue 7 feb 2017.doc

[Guest]

Hello to everyone who are using this thread. I thought that I would give it a try. I may copy across a few of my posts but I'll start with the two that I posted today plus my last full weekly report from Sunday, all on the winter model thread. I have been particularly bullish recently and I am happy for anyone to challenge or support my views with constructive comments. If I post on here directly I will take a more measured approach.  I'll be back later to see if we get some discussion going on these.

EDIT:  One problem that I have just noticed in quoting/copying across these posts is that the automatic chart viewing facility (to progress through a sequence of charts with the arrows at each side) no longer works and each chart has to be viewed individually. I'll check with Paul to see if there is a way around this problem.

1 hour ago, Bring Back1962-63 said:

TIME FOR A GOOD "OLD-FASHIONED" LOOK AT THE FAX CHARTS

TODAY’S  0Z OUTPUT:

               T+6:  0600 TUE FEB 7TH                                   T+24: 0000 WED FEB 8TH                               T+36: 1200 WED  FEB 8TH                             T+48: 0000 THUR FEB 9TH                  

                                                 

            T+60: 1200 THUR FEB 9TH                                T+72: 0000 FRI FEB 10TH                                 T+84: 1200 FRI FEB 10TH                           CURRENT LIVE CHART FOR COMPARISON

                                                    

YESTERDAY’S 12 OUTPUT  (THESE LAST 2 CHARTS ARE UPDATE AROUND 1400 EACH DAY)    

           T+96: 1200 FRI  FEB 10TH                                  T+120: 1200 SAT FEB 11TH                            UKMO 0Z T+120 SUN FEB 12TH                             UKMO 0Z T+144 MON FEB 13TH                   

                                                                    

COMMENTS:

I am surprised that no one has posted all these charts as they show us so much short term detail. Obviously they are all available here on the NetWeather site and can be checked at any time but we need a little analysis.

Firstly, note that the fax charts are today's 0z output (which go up to 1200 Friday),  except the last two which are yesterday’s 12z output (which repeats the 1200 output for Friday as a good comparison and goes out to 1200 Saturday).  I also include the UKMO 0z T+120 and T+144 for comparison.

The T+6, T+24, T+36 and T+48 charts show the fronts stalling over the east of the UK and then returning westwards as the cold air from the east undercuts the remaining Atlantic air. We still do not know how much of the rain will turn to snow during this two day phase. Probably nothing really significant as it all fizzles out. All the time we see the Scandinavian HP building and edging westwards. It is only shown to attain a central pressure of 1050 mb by T+72 on Friday. As I said in my post on page 132, it is already stronger than this and likely to exceed 1050 mb during today (watch this on the live chart) and set to intensify further (my guess is perhaps 1055 mb by later tomorrow). This extra strength may well be important down the line in terms of the HP holding its position as well as forcing more of the cold pool towards us around its southern flank. The minor area of LP (forming on the occluded front) to or over the south-west of the UK is moving away east-south-eastwards and is likely to help the undercutting,  bringing in the easterly slightly more quickly. The Italian LP looks very static now and that should help to prop up the HP and provide a more direct easterly flow as time goes on.

By T+72 onwards, we see a succession of troughs and minor fronts moving west-south-westwards in the flow towards and across the UK. These features plus the upper cold pool(s) mostly associated with them need to be watched carefully. There is plenty of potential for some more widespread snow. The latter period out to the weekend shows a continuation of this pattern with several more disturbances. The UKMO 0z shows the HP expanding both south-eastwards and westwards (perhaps linking with the Azores high to form a loop to the north of us). The LP approaching from the south-west (if that pattern develops like that - plenty of uncertainty) will be hitting some very cold surface air over all of north-west Europe and the UK. This could well produce a good and widespread snowfall. Thereafter, I do not see a big sinking of the HP but rather a strong ridging to the north-west and towards Greenland to set up phase two of this cold spell. My strong hunch is that the HP will be far more resilient sitting over the ever deepening surface cold and remaining close to its current position for over a week or longer. The eventual change to the northerly may actually be quite a smooth transition will little or no slightly less cold period in between. I think that some of the models and the ECM in particular are once again hugely under estimating the strength of the cold block which will be right over us , almost all of Europe , Scandinavia, Russia and way into eastern and central Asia. Very exciting times ahead.

 

 

Edited February 7, 2017 by Guest
Correcting typos and to ensure that all the links and charts work properly.

[Guest]

On 2/5/2017 at 19:25, Bring Back1962-63 said:

WINTER 2016/17 FULL REPORT No. 12 WITH FEBRUARY 5th INPUT

This is by far my most upbeat report of the whole winter (whatever any of the 12z model output might say!)

Brief Review Of The Last Week:

The widely predicted change from the cold continental influence to the more unsettled Atlantic influence was completed early in the week but not without further cold days in the north and north-east at first. The named storms, indicated on much of the model output a week ago, did not reach us but took a more southerly track into France where they named one storm  “Leiv” but fortunately the severest damage was restricted to a very small coastal region in western France. The following storms were less intense.  We were on the northern edge with some rain and briefly some stronger winds in the south and south-west. Although temperatures have recovered to some extent they have (mostly) only slightly exceeded normal on a few days and were generally in single figures with even a little wintry precipitation on higher ground in some parts.

The Current and Short Term Position:

I felt that this milder spell would be brief and kept a careful watch on the European cold block which I have said time and again during the last month has been consistently under estimated by almost all the models. I believe that this is still being under estimated and this time it will greatly assist us in the feed of deeper cold air into the UK by next weekend. In fact, I felt so strongly about this that I started a “Daily European Temperature and Pressure Watch” three days ago. My latest update was posted this morning (see page 92).  The cold block was only pushed slightly eastwards into western Asia. Much of central and eastern Europe only briefly saw temperatures rise slightly above freezing (for a couple of days).

The UK Atlantic spell is being cut short. Fronts will be stalling across the country during the next three days as a Scandinavian HP takes hold.  There may even be a little snow as the fronts return westwards before they fizzle out. Right now, pressure is building strongly from north-west Russia and is already ridging into Scandinavia – just look at my live pressure chart on page 92 and compare that to the 0650 chart. The deep cold is also steadily intensifying in north-west Russia and moving south-westwards into northern Scandinavia. The sub -20c pool of surface cold (some is nearer -30c) and sub -20c 850s are also expanding and moving steadily westwards and south-westwards. I believe that the transition may well be even faster than currently predicted with colder weather installed by mid-week. I also think that there is a good chance that the small area LP that moved across south-west England today will move away into France. Then the fronts associated with the following larger area of LP tomorrow may not make much progress into the UK and there might be a good chance of a new small LP forming on the warm front or near the occlusion which could move away south-eastwards and further undercut the block, introducing easterlies further south into the UK a day or so sooner.

I demonstrated the predicted development of the Scandinavian  HP in another post yesterday (see page 84) where I used all the Met Office fax charts. I had noted that their latest charts (which were issued several hours ahead of the 12z model output – they always give an advance clue to any likely near term changes) were showing the HP being maintained further north and west over Scandinavia and with a better alignment for the easterly on its southern flank. Some of the models are still struggling with the all important detail on this. I indicated this morning that there were already several undercutting LPs propping up the HP. Okay,  I had better post the two live charts now to make my points clearer (but just take another look at all the charts on page 92 to fully appreciate the extent of today’s changes):

EUROPEAN "LIVE" PRESSURE CHART                       EUROPEAN "LIVE" TEMPERATURE CHART

                                 

At this stage, my take on this is that the Scandinavia HP will not sink southwards, at least for quite a few days. I also believe that with this and the under estimated depth and extent of the cold pools (upper and surface cold) that conditions will turn somewhat colder across the whole of the UK sooner than much of the recent model output has suggested.  I do note that the 0z output has mostly upgraded the colder uppers. I am writing this part of my report at 1330 and by the time I post it this evening, the 12z output will have rolled out.  I am expecting further upgrades over the next few runs but perhaps still with the odd single run/single model set back. The models mostly still need to factor in the current extent of the cold and as they update they should reflect these changes in the D3 to D6 range.

Now, I am not trying to score points over anyone (and it would foolish to try to take on the models for any extended period) and I may be wrong about this but let’s look at some more evidence. I noted an interesting point that @johnholmes raised several days ago which I completely agree with. The strength and persistence of HP and/or cold blocks is frequently under estimated by the models. In fact I would say that this is often one of their most serious faults or shortcomings and presents huge timing issues and even leads to quite a different outcome on occasions. In the days when forecasters did not have access to computer models, satellite imagery and all the other modern tools, they often had difficulties in assessing the longevity of these blocks. Much of their forecast was based on pure experience and using analogue charts alongside the current data. As John says, it is amazing that these blocks still present such forecasting difficulties.

Many on here have said, easterly airstreams have been much rarer in recent years. Back in the 1960s to 1980s they were so much more common. Not just in cold winters but we usually saw several of them even in predominantly mild winters. I can recall a great many examples of all sorts of types of easterlies but this is not the time or the appropriate thread to list them now. In broad terms, the most important component was “usually” the Scandinavian HP. Its position, orientation and how it developed was always so important. Some develop as a temporary extension of a Siberian HP. Some develop in situ, often after an Arctic incursion, when the LP fills up quickly and HP forms over the residual surface cold. Some are transient features and some stick around for days or even weeks on end. Some form when there is no cold pool to tap into. I recall a few easterlies with temps hardly below average. Some produce long periods of cold to very cold but completely dry weather. Some produce a few snow showers on exposed coasts but nothing more than a few flurries inland. A few produce much more convective conditions with rather heavier snow showers often merging into longer periods of snow. Isolated cold pools (those that have broken away from the main cold lobe, like the one indicated on one of the GEM runs two days ago (that disappeared on their next run), small disturbances and troughs can produce snowfall, sometimes developing quite unexpectedly.  Streamers can form in the more favoured downwind well aligned spots (like the “Thames Streamer” on a direct easterly flow) and produce many hours of almost continuous snow showers with significant accumulations. There can sometime be more general snow events when Atlantic LPs and their attendant fronts come up against the cold block. Down here in the West Country there have been a number of severe blizzards when stalling fronts undercut the easterly or south-easterly flow. These are rare events but can turn up in mostly mild winters (such as February 1978) as well as in severe winters (with multiple events in 1947 and 1962-63). Sometimes an easterly is swept away rapidly by the Atlantic (probably with the Jet Stream powering up with a more direct attack). Sometimes a LP over Biscay or France veers the flow to the south and pulls in much milder air.

So what sort of easterly will this one be and will it deliver any snow? Unfortunately, the answer is that I do not know for sure but there are some very positive signs. Factoring in some of what I’ve just mentioned, I am very encouraged in the way that this Scandinavian HP is developing. This is from the north or north-east into Scandinavia. There is already a good supply of surface cold. This is now being topped up with even deeper cold as I have already shown. HPs often sit over some of the coldest surfaces available. I feel that there is an excellent chance that once the HP sets up over northern Scandinavia, that it will maintain a similar position for quite a few days.

The next thing is the LP areas on the southern flank. The very latest position on the live pressure chart shows another really encouraging sign – the central European LP is already helping to re-orientate the HP. I think that within 24 hours it will be far more on an east/west or east-north-east/west-south-west axis. This means a more direct easterly. The strength of this flow will be determined by the intensity of the HP and how close are the LP(s) on its southern flank.  The increasingly cold air should then filter south-westwards in this flow.

The south of the UK in particular may well be far enough away from the HP to the north-east to encourage some convective activity. If we can get sub -10c uppers in, then things could start to get much more interesting. For now, I would say just some snow showers on exposed east coasts but all to play for in the finer developments during the next few days.

Next Weekend and Into Week 2:

So how long will this last for and just what can go wrong. I know that some on here like to be more cautious and it can be wise to manage expectations to avoid future disappointments. Others can get taken in by all the ramping with the very bests charts greatly outnumbering the less goods ones being posted (I wonder why!). After all the disappointments we have seen so far this winter as well as in several recent winters it would hardly be surprising to see quite a few members taking a sceptical view. I believe that this will be a rare occasion when things might just go right for us coldies.

This has been a highly unusual winter with persistent blocking restricting any Atlantic influence to the minimum. Blocked winters usually have prolonged cold spells. The vast majority of the blocking this winter has been MLB. This has allowed for some exceptional cold over Europe but we have mostly been just on the outer edge of it. There has been a highly anomalous area of  HP very close to the UK for much of the last three months. Several posters have said if only we could have the HP a little further north. Well your wishes are about to be granted! I believe that there is now an excellent chance of HP being located to our north-east and later to our north or north-west for much of the next six weeks.

Let’s have a look at the Jet Stream. The main arm has taken a more southerly track recently and the northern arm has broken up with a returning flow circling Scandinavia (which may help to maintain the HP or conversely, the HP is partly deflecting the flow of the Jet.

Northern Hemisphere Jet Stream – Current Position:

                         GFS 12z T+6  

          

Moving on to D6, let’s have a look at several cross model Jet Stream charts.  The main arm continues to be deflected to our south. The southern arm drives through the Mediterranean and south of most of Europe. This should carry LPs systems along that path and this will also help to underpin the HP further north.

Northern Hemisphere Jet Stream for Sat 11th Feb – 0100 (with adjusted times to provide an accurate comparison):

                        GFS 6z  T+144                                           NAVGEM 6z +144                               GEFS ens mean 6z T+144 

                   

Another useful indicator for assessing the likely future strength of the Jet Stream in the Atlantic is the thermal contrast between the eastern USA and the adjacent ocean. Right now and for at least the next week much of the USA will continue to have an unusually mild period. Canada is pretty cold but it rapidly turns milder further south. So, nothing here at all in helping to power up the Jet Stream.

Northern Hemisphere Current 2m Surface Temperatures                                                              Northern Hemisphere Current 850s

                                GEFS ens mean 12z T+0                                                                                                                  GEFS ens mean 12z T+0

                                                                                                                             

Northern Hemisphere 2m Surface Temperatures for 1300 Sat Feb 11th                         Northern Hemisphere 850s for Sat Feb 11th – 1300: 

                                         GFS 12z T+144                                                                                                                       GEFS ens mean 12z T+144           

                                                                                                                     

I have seen several poster’s concern over the chance of an Iberian LP drifting northwards over France and pulling in milder air with it. If the southern arm of the Jet continues to blow strongly through the Mediterranean there would seem to be a slim chance of this. In my experience, it is the slacker flows that can be prone to this. Even here, there are some examples of the milder air not being able to penetrate the surface cold and the warmer air is lifted over the cold which can produce far heavier snowfall or occasionally freezing rain. I call these events  “cold southerlies”. They occurred repeatedly in the two epic winters of 1946/7 and 1962/3. In fact most often in the two Februarys. I’m not saying that the 2017 cold spell will be anything like those two winters but entrenched deep cold will take an awful lot to shift it – not a gentle push from the south.

A Brief Look Further Ahead:

I have not yet even mentioned the stratospheric changes and the multiple warmings in the Arctic.  As I said in my report last Sunday (and repeated in several of my updates during the week) there was a good chance that even if the first warming fails to produce a true easterly that there would be one or two further opportunities. I was very reassured to see the latest updates from several of our strat experts like @chionomaniac that the PV should be split for a much longer period. In fact it may well be shattered! The MJO (see later) is predicted to enter its key phases through 6, 7,8 and 1 in the 10 to 15 day period. @Tamara, in her update today, maintained her view that the key background signals should all assist with much greater HLB. 

The result of this could be twofold, both are cold outcomes - either maintain and strengthen the existing Scandi block or encourage height rises towards Greenland with a broad Arctic flow established. In our longest cold spells we have sometimes seen several switches between easterlies and northerlies and back again. There could be a brief milder interlude during any transition and all the models have been struggling with this in terms of timing, extent and how long will it all last. I am going to stick my neck out and say that it will remain cold for the rest of the month (possibly well into the first half of March too) and it will be very cold for quite long periods. How much snow we might get is very difficult to for anyone to predict but the longer the cold spell continues the greater the chances. I am still very optimistic for the initial easterly to produce at least some of the white stuff.

Can it all go wrong – yes it can but I feel that this is our best chance in four years for a memorable cold spell and there is so much positive evidence in favour of it.

Now on to my routine coverage.

Arctic Sea Ice News and Analysis:

The last full monthly report was published on January 5th (next one due very soon). This is a fascinating read and includes a review of the whole of 2016. Please note that the current ice extent map and the comparison chart to the mean are updated daily and are always of interest. Here’s the link for the latest updates:

http://nsidc.org/arcticseaicenews/

This chart shows the current extent of the sea ice (as on February 4th) in relation to the 30 year means.

Source: National Snow and Ice Data Center (NSIDC)

The “rate of recovery” during December was very close to a record and there has been a continued recovery (with several pauses) during January but, despite this, the overall ice extent is still at record lows and remains just below the previous low set during Winter 2012-13.

Arctic Oscillation (AO) 14 Day Ensemble Chart:

Here's the link to the daily charts:       http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

...and here’s the current chart which updates automatically each afternoon:

Note for newbies: The AO index reflects the amount of HLB in the Arctic. A positive +AO reflects very little HLB and a strongly +AO reflects no HLB anywhere in the Arctic. A negative –AO reflects some HLB and a strongly –AO reflects substantial HLB with more intense high pressure and/or more extensive HLB in various parts of the Arctic. This index produced by NOAA is based upon GFS model output and will fluctuate in line with that. Although ECM produce similar data based upon their own output this is not one of their “free-to-view” charts for public consumption.

COMMENT (relating to the AO chart above when it was showing February 4th data - it updates automatically each afternoon):

The Arctic Oscillation is currently negative and many ensemble members go into much stronger negative territory into week 2 (the strongest for the whole winter) but a smaller number of members trend back towards neutral. This reflects the GFS model uncertainty around D8 to D12. A possible switch to HLB and a northerly, a continuation of the Scandi HP or a breakdown  with a milder Atlantic influence.

North Atlantic Oscillation (NAO) 14 Day Ensemble Chart:

Here's the link to the daily charts:                 http://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/nao.shtml (click on the small chart there)

...and here’s the current chart which updates automatically each afternoon:

Note for newbies: A neutral NAO index reflects the close to average state of the mean sea level pressure patterns or the “climatological” norm in the North Atlantic. This would equate to the anomalous high pressure in the south, particularly around the Azores and low pressure stretching from off the eastern USA seaboard in a wide band running north-eastwards to the east of Newfoundland, east of Greenland and through Iceland. A positive +NAO occurs when these patterns are stronger than usual (eg: the Azores high is more intense or more widespread and/or the Iceland low is deeper or more widespread than usual). A negative –NAO reflects a weak Azores high and/or less intense Icelandic low pressure. A strongly –NAO would reflect a reversal of the normal patterns with relatively low pressure in the Azores and high pressure further north towards Iceland. A “west based –NAO” (talked about recently) is when the pressure is higher than usual in the western Atlantic such as around the Newfoundland area). An “east based –NAO would indicate higher pressure than usual in our part of the Atlantic. This index produced by NOAA is based upon GFS model output and will fluctuate in line with that. Although ECM produce similar data based upon their own output this is not one of their “free-to-view” charts for public consumption.

COMMENT (relating to the NAO chart above when it was showing February 4th data - it updates automatically each afternoon):

The NAO is currently positive and most of the ensemble members trend gradually towards neutral but remain slightly positive. Although we have the Scandinavian block much of the Atlantic is still dominated by LP. The NAO is not particularly important at this stage. If the block moves further west, we may see a slightly negative east based NAO later on.

MJO Ensemble charts:

Here are today's MJO ensemble charts for the big 4 (all updated on February 4th) + Kyle MacRitchie’s modified chart (by request following recent discussions) with the live links below should you wish to check any future changes: 

               UKMO   (7 day forecast):                       ECM (14 day forecast):                     NCEP/GEFS (14 day forecast):                 JMA (9 day forecast):                         Kyle MacRitchie (30 day forecast):

         

 

UKMO:     http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ukme.shtml

ECM:       http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ecmm.shtml

GEFS:        http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ncpe.shtml

JMA:         http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/jman.shtml

Kyle MacRitchie   https://weatherandvines.com/?page_id=140                  and his explanatory notes and further guidance:     https://weatherandvines.com/?page_id=128

COMMENT (relating to charts showing February 4th data - they update automatically each afternoon):  What an amazing set of charts – a full house! The big 4 and Kyle MacRitchie all show the MJO entering the keys phases of 7,8 or 1 at very good amplitude. The best signals, I think for several years.  A few of the ensemble members go off the chart in phase 8! This is perfect timing and along with the second (and possibly third) warming events should greatly assist with considerable HLB as we move through week 2.  Over to our experts for a deeper analysis.

Northern Hemisphere Snow Cover:

I show animations for snow cover and sea ice changes. These are produced by the National Ocean and Atmospheric Administration (NOAA).  When you go to their site you can change the date range and go back over 10 years. You can change the speed and pause on any particular day. These are brilliant, very informative charts and great to play around with. I’ve have re-set the links below to show the last 2 weeks from January 21st  to February 4th but you can change these again on the site:

a) Animated Northern Hemisphere Snow Cover Changes (updated by NOAA February 4th):

https://www.ncdc.noaa.gov/snow-and-ice/snow-cover/nh/20170121-20170204

....and here is their current chart:

b) Animated Europe and Asia Day Snow Cover (updated by NOAA February 4th):

https://www.ncdc.noaa.gov/snow-and-ice/snow-cover/ea/20170121-20170204

....and here is their current chart:

COMMENT: 

Part of central and much of eastern and south-eastern European is still snow covered. There continues to be well above average snow cover over northern Asia and this has expanded even further southwards and south-westwards – in fact it is quite exceptional. Scandinavia is fully snow covered, except the south of Sweden (the high central plateaus usually have pretty complete snow cover for most of an average winter). The extensive snow cover over North America has declined during the recent much milder conditions and this is likely to continue during the coming week or so

The extensive snow cover over west Asia, Russia, eastern Europe and Scandinavia is another very important piece in the jig-saw as far as our forthcoming cold spell is concerned. This should greatly assist in getting the deeper surface cold in and maintaining very low temperatures for much longer – strengthening the block further.

 

Current Arctic Regional Surface Temperatures:

GEFS ens mean– Northern Hemisphere Current Temperatures for February 5th 1900 (12z – 1300 T+6):

and here’s the link to live charts if you wish to view future changes (updated 4 times a day):

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=6&mode=1&carte=1

Here is my selection of Arctic Regional Temperatures:

The the previous readings from my last full report are shown in brackets alongside

North Pole:       -20c to -24c   (-20c to -28c).

Baring Sea/High Arctic:    -16c to -24c  (-8c to -16c).

Scandinavia:  south  -4c to -8c  (mostly -4c);  north  mostly -8c  (mostly -4c).

Northern Siberia:    -32c to -40c   (-24c to -40c).

North West Russia:     -16c to -20c  (-12c to -24c)

North-east Europe:     0 to -4c   (-8c to -12c).

Greenland:           -16c to -32c   (-20c to -40c)

Canadian Arctic:     -24c to -32c (-16c to -32c).

Alaska:      -12c to -20c    (-8c to -16c).

Please note:  For land masses I have tried to focus on readings away from the coasts and away from any mountainous areas.   You can follow the trends by looking at the latest data at any time from now on. It is vital to note the time of day to take account of daytime/night time variations. So for like for like comparisons, for example the 1900 charts for each day should be available to view from the 12z (T+6) updates which are published around 1600 to 1700 or about 4 to 5 hours later.

Svalbard Daily “Maximum” Temperature Forecast for 10 Days:

Here are the links to the 3 Svalbard stations that I am monitoring together with a summary of D1, D5 and D9 values:

Central/West Svalbard – Longyearbyen 28 m asl:   

http://www.yr.no/place/Norway/Svalbard/Longyearbyen/forecast.pdf

February 6th    +3c;            February 10th  +1 c;            February 14th    -5c.

North-West Svalbard – Ny-Alesund:  

http://www.yr.no/place/Norway/Svalbard/Ny-Ålesund/forecast.pdf

February 6th   +2 c;            February 10th  +1c;            February 14th    -5c.

Central South Svalbard – Sveagruva:   

http://www.yr.no/place/Norway/Svalbard/Sveagruva/forecast.pdf

February 6th    +2c;            February 10th   -2c;            February 14th    -8c.

Please note that the links above will update automatically at frequent intervals throughout the day. They are the Norway met office’s predictions. We need to be aware that these are only a forecast that is subject to change and I am told that the Arctic surface temperature forecasts are not completely reliable even at quite short range. 

BRIEF COMMENT:

Temperatures have risen just above freezing during the last few days with one of the warmest periods of the winter. This followed one of the coldest periods in the previous week (even below the 30 year means). The southerly winds brought quite a bit of snowfall with more to come. It is only after next weekend that temperatures are set to fall again. To put the above figures into context, here is a link to the main Longyearbyen site:  

http://www.yr.no/place/Norway/Svalbard/Longyearbyen/statistics.html

This shows monthly means and actual highest/lowest temperatures recorded during this winter and goes back further. Svalbard has been seeing “maximum” temperatures often running at 8c to 10c above their long term average throughout most of 2016. This has been the pattern for several years and is reflective of the warming Arctic and record low sea ice cover.

Final Comment:

As I’ve already said, I am extremely positive about the forthcoming very cold spell. I feel that there is a good chance that this will last for at least 2 to 3 weeks and perhaps well into March. Now will I be eating humble pie next weekend – I do not think so!

Next Update:

My next full weekly report should be on Sunday evening, February 12th.

 

 

[Guest]

3 hours ago, Bring Back1962-63 said:

DAILY EUROPEAN TEMPERATURE AND PRESSURE CHECK No. 5  

FURTHER GREAT NEWS - THE DEEP COLD POOL IS MARCHING WESTWARDS INTO EUROPE

In the build up to our cold spell, I feel that it will be useful to keep up-to-date with the current and trending temperature and pressure changes in Europe. I will try to produce these on a daily basis for the next few days around 0730 to 0800 (although I am away on a business trip this Friday so no update then and Saturday’s will be around 1300). This will show how the pattern is evolving and allow us to monitor the extent and the severity of the cold that we might expect.

Firstly, I simply do not understand some of the negativity on here. Here is a summary of my take on developments. Our weather will be coming from an easterly quarter for much of the next 10 days and we will soon be part of a massive cold pool that covers a vast amount of western Asia, Russia and north-east Europe and now Scandinavia and it’s all heading our way. There is no energy in the Atlantic to shift this at all as far as the eye can see and the surface cold will almost certainly become intense and entrenched. Temperatures almost always turn out lower than initially predicted in this type of set up. There will also be some extremely low dew points and the 850s, despite a greater variability, will be very low at times with several breakaway colder pools likely to head down through the flow.

There are more than strong hints of a switch to a broad northerly later in week 2 and later in the month we may see switches between northerlies and easterlies a few times with the HLB somewhere between Scandinavia and Greenland. For more details and analysis of this please refer to my last full report on Sunday (see page 105). Since then everything has been going in the right direction. The models will still fluctuate on the finer detail for the first week (very uncertain where and how much snow we shall get but at least some seems highly likely) and even more so in week 2 nailing down the transition from “cold” conditions to “cold” conditions (no typo there !).  At worst, just several days of slightly less cold weather.

Now, I shall pick up from my last “check” on page 112. This took us to February 6th.

European Surface Temperature Charts:

                 Current "live"                                Feb 7th 0650                                    Feb 6th    1250                                  Feb 6th  0650                                  Feb 5th 1250

     

Note that it is important to allow for min/max temps when comparing the charts. The 0650s are usually close to the minimums and the 1250s are usually close to maximums.

COMMENT:  Just look at how much that sub -20c purple area has expanded. Ahead of that, almost all of Scandinavia except for a few coastal spots is sub -5c with a lot of sub -10c temps. The darker blue shades of sub -5c has moved through eastern Europe and reached central Europe. It's all heading steadily towards the UK. All this can be seen by comparing the two "0650" and the two "1250" charts.

GFS  0z February 7th T+6 European Charts: 

            2m Surface Temps                                   850 Temps                                      500 hPa Temps

       

COMMENT:   Compare today's charts (above) with yesterday's  (below).  Note the further expansion of the "purple shades" area of sub -20c surface temps with a greater area below -24c and even a patch of sub -32c temps (light grey). The only piece of slightly less good news is that the pool of sub -20c 850s is slightly smaller but this is more than countered by the increase in the area of the sub -8c and -12c temps. There is quite a large area of breakaway sub -12c temps (with a centre of sub -16c temps) moving south-westwards through southern Scandinavia and northern Europe. Another extremely encouraging sign is the re-orientation and path of the sub -12c temps. Note how that part of the pool is now heading straight for the whole of the UK rather than slightly to our south. This change has happened as I predicted simply because of the development and changing shape of the Scandinavian HP pulling the cold through westwards on its southern flank.

GFS 0z February 6th T+6 European Charts: 

                2m Surface Temps                              850 Temps                                      500 hPa Temps

        

European Surface Pressure Charts:

               Current "live”                                   Feb 7th 0650                                   Feb 6th    1850                               Feb 6th  0650                                Feb 5th    1850  

                                         

   Current Met Office Fax: 0600 Feb 7th            GFS 0z February 7th T+6                 GFS 0z February 6th T+6    

                                                     

COMMENT:  Our Scandinavian anticyclone has intensified further and has just reach 1049 mb and is still slowly intensifying. It looks like it will reach some way over 1050 mb (perhaps as high as 1055 mb) which is more intense than any of the models were predicting (at least up to the 12z and 18z output yesterday). This should help strengthen the easterly flow and push the deeper cold (surface and uppers) closer to the UK more quickly than predicted. The centre of the HP is still edging very slowly west-south-westwards. I feel that it will maintain a very similar position for many days. The exact orientation of the flow will be partly dictated by the Mediterranean LP which has remained centred over Italy for over 36 hours now. This looks like a highly stable set up in terms of position and longevity. The flow looks like it will be east-south-easterly initially (with due east winds) as it moves into the UK during Wednesday and Thursday. Then, as the deeper cold air pushes around the HP it looks like the flow will veer slightly more to a direct easterly (with east-north-easterly winds). This should produce at least some snow flurries but there may be some snow showers along exposed eastern coasts as soon as Thursday (that's after perhaps a little snow as the stalling frontal system pushes back westwards tomorrow with the colder air already undercutting it). Then we need to look out for troughs and other disturbances running west-south-westwards through the flow. That cold front shown on the current Met Office chart is the leading edge of the much deeper cold air and one to keep an eye on. 

Overall, everything continues to move in the right direction - there is no need to worry about the variable 850s as they'll be generally low enough for any precipitation to fall as snow from late Thursday onwards as the dew points will be falling to sub zero by then. There will be pools of much lower 850s at times which might introduce greater convective activity - so there will be some good potential for at least some snow. We should be able to get a better idea of this by Thursday. I'll be back tomorrow.

 

 

[Rollo]

Hi again David,the gnashing of teeth at the moment reminds me of early February 63' particularly in Newcastle,I forget the exact date (could check) but the forecast for the next day showed a depression off the S.W. approaches pushing mild weather North eastwards into Scotland however I woke up to find light snow falling  and that the low had decided to move eastward prolonging the long cold spell by quite some time. I know times are different what with global warming etc but I find it incredible to think that what to me in the past has always proved a durable cold spell of at least  two weeks could disappear down the pan so rapidly.

 

 

 

[Guest]

On 2/7/2017 at 11:30, Rollo said:

Hi again David,the gnashing of teeth at the moment reminds me of early February 63' particularly in Newcastle,I forget the exact date (could check) but the forecast for the next day showed a depression off the S.W. approaches pushing mild weather North eastwards into Scotland however I woke up to find light snow falling  and that the low had decided to move eastward prolonging the long cold spell by quite some time. I know times are different what with global warming etc but I find it incredible to think that what to me in the past has always proved a durable cold spell of at least  two weeks could disappear down the pan so rapidly.

Hi again Mike, this happened repeatedly in 1963. Time and again the forecast was for a little snow followed by much milder Atlantic weather but each time the LP dived south-eastwards producing much heavier snowfall and continuing the cold spell. Here's a link to the archive charts:

http://www.meteociel.fr/modeles/archives/archives.php?day=8&month=2&hour=0&year=1963&map=0&region=&mode=2&type=ncep

and here are several charts showing exactly what happened on February 8th to 10th 1963. I'm not sure if this is the precise event that you are referring to.

                 

Right after 2 posts today, I need to get on with some work. I'll check back later.

 

ADDITIONAL COMMENT:

Like all new things, it will take time for this thread to get up and running. Those, like me, who use it, will like the slower pace but it's a little too slow right now! I am away on business for a couple of days but I'll make a real effort early next week to produce a few posts designated to this thread only which will, hopefully, provoke some interesting discussion. So, I'll be back - meanwhile - keep posting!

Edited February 9, 2017 by Guest
Additional comment

[Rollo]

Thanks David that's the one.

[Nouska]

This thread is looking rather lonely and the other one, I hope, has reached its nadir today.

People are fretting about the Scandinavian block sinking but have they really looked at why that is being modelled. An animation...

Where's the Atlantic in the picture?

It is not sinking because of a raging Atlantic jet stream riding over the top - it is being sunk by a huge chunk of Siberian vortex putting pressure on it!  What happens when you sit on a big round beanbag; it squishes out to the sides ...on one side is Greenland.

As @MattHugo says in the model thread, give it time and have a bit of patience.

 

 

[Glacier Point]

Not sure the upstream teleconnections are as favourable as being advertised by RMM MJO plots.

200hPa velocity potential is much further east than would be considered for phase 8, and threatening an Indian Ocean evolution:

That's more phase 1 territory which is no where near as favourable for high latitude blocking. Factor in the displacement of the upper vortex towards Siberia and you get a signal for Euro ridging as per NWP extended means. Very similar to the mid / late November episode.

That's not to dismiss the text book spike in tendency in angular momentum that has occurred on the back of the evolution of the tropical wave through the Pacific, but my take on that would be for more of a hit to the stratospheric vortex at the end of the month and more robust blocking signal to the NE / N at this time, and into early March, although for the lowland snow chasers that's too late I appreciate.

[stodge]

Afternoon all

Thanks you for the post and the insight, GP.

GFS 06Z OP in far FI looks to a renewed round of warming though more from the southern Eurasian side then the Siberian initially. The initial response will presumably be to push the PV back over to the Canadian side - whether far enough to allow blocking to the NE/N fairly quickly or not I don't know.

Given the traditional 10-14 day response, I think we're looking at a 21-day period of milder conditions from the end of the current cold spell next Tuesday to the next blocking episode in March.

March isn't too late for lowland snow by any means under the right synoptics and indeed one could argue a warmer North Sea in March provides more convective potential.

I'd like to argue for the Greenland option but that would require some changes on what looks like the pattern - GFS danced with it yesterday dropping a lobe of the PV into Scandinavia and offering a N or NE'ly airflow over the British Isles. I'd hoped a clean lift of the PV to Siberia would enable the height rises and I'm still not wholly convinced that door is closed but I'm much less hopeful than I was this time yesterday.

 

[johnholmes]

using the link below with Doncaster as the skew-t it is clear to see how the convection is much more limited than predicted on the post I made above, no more than 6-7,000 ft or so, rather than 10,000 ft at its maximum. Also the change in the upper air at lower levels is shown clearly as the less cold air moves in from about the 13th.

https://www.netweather.tv/secure/cgi-bin/premium.pl?action=cskew;sess=be55690ed5693fa76a2315b6e6772f36

For interest type any town/city in to see how the upper air (lower regions) changes over the 180hours. Even further north the convection is now predicted to be less marked.

Edited February 8, 2017 by johnholmes

[Singularity]

2 hours ago, Glacier Point said:

Not sure the upstream teleconnections are as favourable as being advertised by RMM MJO plots.

200hPa velocity potential is much further east than would be considered for phase 8, and threatening an Indian Ocean evolution:

That's more phase 1 territory which is no where near as favourable for high latitude blocking. Factor in the displacement of the upper vortex towards Siberia and you get a signal for Euro ridging as per NWP extended means. Very similar to the mid / late November episode.

That's not to dismiss the text book spike in tendency in angular momentum that has occurred on the back of the evolution of the tropical wave through the Pacific, but my take on that would be for more of a hit to the stratospheric vortex at the end of the month and more robust blocking signal to the NE / N at this time, and into early March, although for the lowland snow chasers that's too late I appreciate.

Hi GP,

How sure can we be of the GFS outlook for the velocity potential and its sharp move away from the fairly close alignment with the MJO that we currently have?

It seems strange to me that so many major forecasting institutes would go with a mostly cold month if the model handling of this aspect was being taken very seriously. Or is this a very recent development from the model(s); I've not had time to keep tabs on it all lately. TIA

[damianslaw]

Some very good posts in this thread. I like the idea of such a thread, and hope to see it again next winter. Insights might suggest just like winter 05/06, the only time we establish high lattitude blocking is just outside the winter season, i.e. mid/late Nov and early-mid March, all rather frustrating it has to be said. ECM is hinting though that we may see some form of height development towards Iceland at least, in 10 days time, with a deep trough through scandi and very cold uppers there, wouldn't take much to swing in a very cold unstable NE flow thereafter.

 

[Singularity]

11 hours ago, damianslaw said:

Some very good posts in this thread. I like the idea of such a thread, and hope to see it again next winter. Insights might suggest just like winter 05/06, the only time we establish high lattitude blocking is just outside the winter season, i.e. mid/late Nov and early-mid March, all rather frustrating it has to be said. ECM is hinting though that we may see some form of height development towards Iceland at least, in 10 days time, with a deep trough through scandi and very cold uppers there, wouldn't take much to swing in a very cold unstable NE flow thereafter.

 

You've picked out an interesting case there; surprisingly, a 500 mb height composite for Feb 2006 shows well above normal values just NW of the UK, despite the archives showing that corresponding SLP patterns were transitory until late in the month;

   

The first is a brief toppler and the following three show a ridge that toppled but was 'propped up' by low heights over Europe and then the door opened for height rises to the NW in response to some MJO phase 3 activity. 

It sure did produce a great pattern by the end of the month but it was too late for many in the south -  I remember forecast snow showers turning out to be sleet and rain.

 

Goes to show that an extremely anomalous pattern can define a monthly mean height composite even if it only affected the final five days of the month! 

Question is, if (note if) we can retain a phase 8 signal instead this year, can a similar response be attained, but about a week sooner given the earlier arrival of supportive MJO activity?

[stodge]

Morning all

Still plenty of options on the table in the mid term this morning. The pattern of a slowly sinking Scandinavian HP (option 2 from my contribution from the other day) combined with a strong LP system near Iberia mean the airflow swinging from East to South over the next few days. Unusually for a "breakdown", this isn't happening because of an Atlantic incursion. Rather, it's a combination of the PV displacement to Siberia carrying energy over the far north and suppressing the HP and the failure of the Atlantic to provide a strong counterbalancing southern arm to hold the HP in a halfway house between HLB and MLB which is driving the evolution.

Beyond, there is, to pout it mildly, a lot of confusion. Fans of cold will want to see this morning's ECM verify:

Plenty of interest in this chart but two obvious points are the moribund Atlantic and the clean lift of the PV out of NE Canada/Greenland toward NW Russia.. Clearly, the opportunity exists for a height rise over Greenland and for the trough to drop into Scandinavia which offers the option of a N or NE flow further south.

GEM goes a very different route perhaps more strongly following the hint of an Indian Ocean solution on the MJO. The other thing to note is remnant PV energy hanging back over Greenland preventing a height rise allowing heights to build into Europe from the SW.

GFS 00Z OP at the same time. Closer to GEM than ECM it has to be said. Interestingly, the PV is moving more toward Siberia than Scandinavia but there's no sign of a Greenland height rise but a less aggressive ridging into Europe but the net effect is to bring back those SW'ly zephyrs beloved of some.

The GEFS for that time offer a huge range of solutions as you might expect and the lack of a clear signal speaks volumes for the current situation.

Developments in the stratosphere remain of interest going forward - I confess to my lack of knowledge on this - but I note the 10HPA temperature warming from -76 now to -64 in a fortnight which would suggest a weaker and more disorganised PV from mid month.

I think it's odds against a successful "Greenland " option at this point though it's certainly not to be ruled out. With a quiescent Atlantic, the possibility for a new Euro block remain present though more south based than the one we are currently enjoying/enduring (delete as appropriate). Without that, I think we're 3 weeks off our next cold spell once this ends but I'm less certain than I was yesterday.

The 06Z OP has rolled out as I've put this together and in FI a lobe of energy is sent back into Greenland but is almost immediately expelled back over Canada - curious. Could this be the immediate response to the next warming phase on the Siberian side or is this a "default" response to a messy PV displacement ?

We'll see. 

[Singularity]

I've been keeping an eye on these and it has to be said that the trends do not match the model output when applying the theoretical hemispheric responses; the U200 has adjusted more toward phase 8 from 1, and the U850 is less into 1 than it was, while OLR remains indicative of C Pacific activity, all of which suggests HLB is more likely than not to crop up to the N or NW of the UK - yet the models have moved strongly away from this over the past 24 hours.

However, if we look at experimental MJO-filtered products we see a different picture of tropical signals, suggesting that some other tropical phenomena are interfering with the classic Wheeler-Hendon diagnosis;

There you have the upper wind signal into phase 1, and the centered plot actually reflects this more than the OLR progression.

It's puzzling that such strong phase 1 could follow phase 8 like that without being some kind of E Pac signal in disguise, but looking at Hovmöllers it seems as if the W. Africa-IO signal is independent of the Pacific developments (is it really though - if anyone knows for sure please do let me know, thanks). This raises the major question - could this have been foreseen back in late January for example? All I saw was uncertain projections and disagreement between models masking the true picture at that range so my take on the answer is quite simply 'nope!'

So it seems there is still much important work to be done when it comes to understanding what periodically can be among the most major driving forces behind the global weather patterns - and one which has knock-on effects on how the stratosphere evolves as well!

[stodge]

Afternoon all

As anticipated, we are set to move into a milder spell of period governed by a weak atlantic and rising heights over Europe keeping the British Isles in a broadly SW'ly pattern. This process starts from the middle of next week and in my view is going to last at least three weeks taking us through the rest of February into March.

The re-location of the PV over to Canada has provided the opportunity for HLB to develop from the Siberian side supported (from the east) by a lobe of PV further over Siberia.

Unfortunately, the next move of the PV is back toward Siberia over the Pole and that causes the Scandinavian HP to sink. IF the PV had re-strengthened over Canada, we'd have seen a more typical "battleground" situation (with all the possibilities) but as I argued the other day, this is an atypical "breakdown". You'd normally expect a fired-up Atlantic to push up against the block and ease it back to the east but the PV's renewed move (presumably based on weakening via warming) back to Siberia cuts off vital support to the Scandinavian HP and so it sinks.

You might expect from such a move to see heights rise over Greenland as the PV exits but the displacement is far from clean or complete and indeed enough residual energy exists over North Greenland and NE Canada to prevent heights so we see a height rise over Europe instead and while the Atlantic remains subdued none of that helps a synoptic pattern leading to cold.

The renewed burst of warming (again from the Siberian side) in FI:

Unfortunately, this has the predictable response of sending the PV back over to Canada/Greenland. Had the warming come from the Canadian side, we'd have seen the PV head for Siberia and the chance of Greenland height rises would have increased but as it is the PV goes "home":

We end February with what looks like a strong PV though that may be an illusion of sorts. Given the usual 10-14 day response to the initial warming, assuming the warming hits on or about the 22nd, we're looking at March 4th-8th for the tropospheric response which might be another attempt to build a Scandinavian ridge so that's three weeks overall of milder conditions from Tuesday next week.

None of this is unusual - winters often have a spell of cold in early February which blows out followed by a warmer almost pre-spring interlude before a sudden reversion to colder conditions and this might be as the PV weakens and is displaced to a more favourable location for advantageous HLB for the British Isles. I'm NOT suggesting a 2013-style scenario but I do think early March could see a notable pattern change from something quite benign to something rather less so.

The path to very cold starts from very mild has always been my motto and we may well have some above average values in the next fortnight or so.

What changes this ? We need a clean lift of the PV out of NE Canada/Greenland to Scandinavia. Without that, pressure cannot rise across Greenland.

To be honest, most of us coldies would sell our souls (and probably those for our nearest and dearest as well) for this chart to verify. The key is the lack of residual PV energy over NE Canada and especially Greenland which allows for heights and at the same time the trough drops beautifully into Scandinavia opening the door to a very cold N'ly.

I'd like to say it was the form horse - in all honesty, at this time, I can't.

[Singularity]

3 hours ago, stodge said:

The renewed burst of warming (again from the Siberian side) in FI:

Unfortunately, this has the predictable response of sending the PV back over to Canada/Greenland. Had the warming come from the Canadian side, we'd have seen the PV head for Siberia and the chance of Greenland height rises would have increased but as it is the PV goes "home":

Thanks for the detailed update Stodge - but there is one aspect I must question; that which I have quoted.

You see, while that warming goes on at 10 hPa with the vortex displaced toward the Atlantic sector/Greenland, down at 30 hPa the situation is almost the reverse;

I don't see how the 10 hPa vortex position can influence the troposphere if at 30 hPa it's tilted all the way over to Siberia.

What actually appears to be taking place in recent GFS runs is the development of some cross-polar ridging in response to the strat. warming which as seems to have been a major habit of the past half-decade is aligned such that cold air feeds across from Siberia to C/E. Canada and serves as a catalyst for deep LP development - though the position of this has been shifting from run to run and it remains to be seen whether the cross-polar ridging will indeed take on that alignment.

 

I am though developing a (currently very speculative) theory that the warming patterns in the Arctic are encouraging stratospheric setups which move Arctic air between the continents, this being a result of the fact that the N. Hemisphere has oceans on two sides and large landmasses on the other two and how the oceans allow far more poleward heat transport in the winter months. I am seriously hoping to be wide of the mark as it does not bode well for seeing many interesting winters in the UK from a snow perspective!

[Catacol]

5 minutes ago, Singularity said:

I am though developing a (currently very speculative) theory that the warming patterns in the Arctic are encouraging stratospheric setups which move Arctic air between the continents, this being a result of the fact that the N. Hemisphere has oceans on two sides and large landmasses on the other two and how the oceans allow far more poleward heat transport in the winter months. I am seriously hoping to be wide of the mark as it does not bode well for seeing many interesting winters in the UK from a snow perspective!

An interesting idea. I am certainly interested myself in learning more about the impact of the severe reduction of arctic sea ice and consequent energy absorption and release. I have still not really read a convincing explanation for the massive reduction in arctic ice... but it is an observational fact and even the most basic understanding of physics suggests huge consequences in the energy budget over the pole. Some of the patterns of surface temperature this season, for example, have been extraordinary. If poleward heat transport is accelerated further by ice loss and the temperature gradient between the cold continents and warm oceans is increased over time then we are left with more potent cyclogenesis and increased warming of any airflow heading towards us from the pole perhaps other than a true Siberian easterly... never an easy win.

Are we entering a world where our only real hope for a decent winter blast in the uk revolves around us being right at the lowest point of the sun cycle as a means of reducing atlantic westerlies and giving some background space for height rises? I worry a great deal about the pole and about the Greenland ice sheet and where we are heading over the next 25 years in this part of the world. I don't see any swift reversal in the gulf stream - but I can see a collapse in northern ice reserves such that the feedback rate of energy absorption in the arctic propels ocean levels upwards and reduces the depth of cold that we can potentially tap into during winter. It is another observational reality that since arctic ice loss has accelerated the cold uppers that tend to approach our shores are much watered down when compared to the past.

The last 2 winters have left me quite gloomy. Last year we had a monster Nino that reversed the QBO. How much more frequent will significant pacific driven events become? This year we had some decent building blocks, but then even with an atlantic utterly shorn of any power or influence the air has been tepid and marginal scenarios have delivered  more rain than snow. And overall we go from a massively wet winter last year to an extremely dry one this year. Not heard official stats - but how close to record dry are we?

I'll be alright in my own lifetime. Grandchildren? Not so good for them.

[blizzard81]

20 hours ago, Catacol said:

An interesting idea. I am certainly interested myself in learning more about the impact of the severe reduction of arctic sea ice and consequent energy absorption and release. I have still not really read a convincing explanation for the massive reduction in arctic ice... but it is an observational fact and even the most basic understanding of physics suggests huge consequences in the energy budget over the pole. Some of the patterns of surface temperature this season, for example, have been extraordinary. If poleward heat transport is accelerated further by ice loss and the temperature gradient between the cold continents and warm oceans is increased over time then we are left with more potent cyclogenesis and increased warming of any airflow heading towards us from the pole perhaps other than a true Siberian easterly... never an easy win.

Are we entering a world where our only real hope for a decent winter blast in the uk revolves around us being right at the lowest point of the sun cycle as a means of reducing atlantic westerlies and giving some background space for height rises? I worry a great deal about the pole and about the Greenland ice sheet and where we are heading over the next 25 years in this part of the world. I don't see any swift reversal in the gulf stream - but I can see a collapse in northern ice reserves such that the feedback rate of energy absorption in the arctic propels ocean levels upwards and reduces the depth of cold that we can potentially tap into during winter. It is another observational reality that since arctic ice loss has accelerated the cold uppers that tend to approach our shores are much watered down when compared to the past.

The last 2 winters have left me quite gloomy. Last year we had a monster Nino that reversed the QBO. How much more frequent will significant pacific driven events become? This year we had some decent building blocks, but then even with an atlantic utterly shorn of any power or influence the air has been tepid and marginal scenarios have delivered  more rain than snow. And overall we go from a massively wet winter last year to an extremely dry one this year. Not heard official stats - but how close to record dry are we?

I'll be alright in my own lifetime. Grandchildren? Not so good for them.

Good post. However, there is the opposite side of the coin isn't there? What I mean is what about the long mild run of winters the UK experienced back in the 1920's and 30's as well as the early to mid 70's? Low Arctic sea ice cannot be blamed for these. 

[Singularity]

6 hours ago, blizzard81 said:

Good post. However, there is the opposite side of the coin isn't there? What I mean is what about the long mild run of winters the UK experienced back in the 1920's and 30's as well as the early to mid 70's? Low Arctic sea ice cannot be blamed for these. 

Good point there, and I don't see the changing Arctic as an absolute controlling factor - just something nudging the balance of probability in perhaps concerning directions.

@Catacol I actually have the inverse concern regarding storminess in the UK; as this tends to occur with the milder air on the SE flank during times when maritime/continental contrasts come into play, it's the Eastern Seaboard of the U.S. for example that may be in trouble there. We could if anything see a reduced tendency for storms to come our way, as the polar boundary migrates increasingly far north by way of adjustment to the new climate regime in which the Arctic cold pool is increasingly small and weak. A predominance of mid-lat blocking such as we've seen this winter ties in well with this theory. A notable side effect is that the most major cold pools in the N. Hemisphere tend to exist either over Greenland or across the mid-high latitudes of Asia. The former may encourage storms to track SW-NE past the mid-lat highs across or near the UK - another behaviour seen again and again this winter. The latter, in combination with the mid-lat highs tending to build across the UK, places southern parts of Europe at great risk of well below normal temperatures and snow in unusual places. Also a feature of this winter.

I have been hesitant to consider this winter as a preview of what may become the norm once the Arctic changes are complete (I know I should say if but given the state of affairs it seems like only a matter of time now), given that after all, there was some MJO activity in Dec and to some extent in Jan that is known to increase mid-lat blocking in our vicinity, and perhaps the unusual storm tracks have some connection with the very positive AMO state of late (not yet researched)... but gradually I have found this to be a more compelling idea, as other explanations have been placed in the 'unlikely' drawer following investigation. I expect the next few years may tend to favour HLB more through low solar forcing so this may distort the picture and mean it's near a decade before meaningful conclusions can actually start to be drawn regarding whether the climate shift I have outlined is indeed coming together already.

Now, who's betting on a Mediterranean summer?  Oh if only the wintertime pattern rules were all that applicable to the summers! 

[knocker]

On 2/10/2017 at 16:54, Catacol said:

An interesting idea. I am certainly interested myself in learning more about the impact of the severe reduction of arctic sea ice and consequent energy absorption and release. I have still not really read a convincing explanation for the massive reduction in arctic ice...

 

I did post a recent paper on this in the New Research thread

Simulated Atmospheric Response to Regional and Pan-Arctic Sea-Ice Loss

Quote

Abstract

The loss of Arctic sea-ice is already having profound environmental, societal and ecological impacts locally. A highly uncertain area of scientific research, however, is whether such Arctic change has a tangible effect on weather and climate at lower latitudes. There is emerging evidence that the geographical location of sea-ice loss is critically important in determining the large-scale atmospheric circulation response and associated mid-latitude impacts. However, such regional dependencies have not been explored in a thorough and systematic manner. To make progress on this issue, this study analyses ensemble simulations with an atmospheric general circulation model prescribed with sea-ice loss separately in nine regions of the Arctic, to elucidate the distinct responses to regional sea-ice loss. The results suggest that in some regions sea-ice loss triggers large-scale dynamical responses whereas in other regions sea-ice loss induces only local thermodynamical changes. Sea-ice loss in the Barents-Kara Sea is unique in driving a weakening of the stratospheric polar vortex, followed in time by a tropospheric circulation response that resembles the North Atlantic Oscillation. For October-to-March, the largest spatial-scale responses are driven by sea-ice loss in the Barents-Kara Sea and Sea of Okhotsk; however, different regions assume greater importance in other seasons. The atmosphere responds very differently to regional sea-ice losses than to pan-Arctic sea-ice loss, and the latter cannot be obtained by linear addition of the responses to regional sea-ice losses. The results imply that diversity in past studies of the simulated response to Arctic sea-ice loss can be partly explained by the different spatial patterns of sea-ice loss imposed.

 

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0197.1

This has also been covered in a number of other papers including this one by Dr. Francis

Evidence linking rapid Arctic warming to mid-latitude weather patterns

Quote

Abstract

The effects of rapid Arctic warming and ice loss on weather patterns in the Northern Hemisphere is a topic of active research, lively scientific debate and high societal impact. The emergence of Arctic amplification—the enhanced sensitivity of high-latitude temperature to global warming—in only the last 10–20 years presents a challenge to identifying statistically robust atmospheric responses using observations. Several recent studies have proposed and demonstrated new mechanisms by which the changing Arctic may be affecting weather patterns in mid-latitudes, and these linkages differ fundamentally from tropics/jet-stream interactions through the transfer of wave energy. In this study, new metrics and evidence are presented that suggest disproportionate Arctic warming—and resulting weakening of the poleward temperature gradient—is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier), although not uniformly in space or by season, and that highly amplified jet-stream patterns are occurring more frequently. Further analysis based on self-organizing maps supports this finding. These changes in circulation are expected to lead to persistent weather patterns that are known to cause extreme weather events. As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.

http://rsta.royalsocietypublishing.org/content/373/2045/20140170

Edited February 11, 2017 by knocker