Model Output Discussion - 1st February Onwards 12z--->

[Winter Cold]

Its very annoying that we dont have any cold 850s around. The trough disruption looks very similar to the last time that happened recently, and we did indeed get some snow from that. There were a few posts the other day suggesting it might go the same way as last time but the 850s were shown a little lower a few days ago. I presume at this late stage its not possible for things to swing back?

 

I know were clutching at straws but it would have been something good to discuss

Edited February 11, 2015 by Winter Cold

[Daniel*]

GFS 12z has colder interludes so not a predominantly mild outlook by no means, at times quite chilly do not pack away your gloves & coats yet. Snow showers possible towards N Scotland - what appears as dull does not always equate to warm sunny days in February based on time of year. For those that are looking at D10 onwards charts it is to go from A > B than skip a step and go from A > C. Just sayin' I think we will have 1 more bite at the cherry, for something more juicy final 3/4 into early March, has my attention, time is still on our side...

Edited February 11, 2015 by Daniel*

[winterof79]

Definately a signal for our resident high to do a Tamara.It is a wait but who ever said the weather would do as we say?

 

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=384 . There are numerous cold options in there.

 

 

This is a peach

Edited February 11, 2015 by winterof79

[Winter Cold]

Well a different idea for the end of the GFS 12z from the 6z......but we'll still take it!

 

[TEITS]

Manchester Winter Index says otherwise

https://forum.netweather.tv/topic/81936-winter-2014-15-thread/?p=3169473

Well according to the stats I have just looked at Manchester has recorded 12 days when the min dropped below freezing. The lowest min temps was -5C recorded on the 19th Jan, 2nd Feb. So rather poor if I was honest. My lowest  min in Peterborough is only -4C!

 

Still the 12Z GFS shows why winter may not yet be over.

 

http://www.wetterzentrale.de/pics/Rtavn3841.gif

Edited February 11, 2015 by TEITS

[Alexis]

Manchester Winter Index says otherwise

https://forum.netweather.tv/topic/81936-winter-2014-15-thread/?p=3169473

 

The index is [10 x (the number of days of falling wintry precipt)+(number of days with lying snow)+(number of nights with a minimum of 0C or less)] divided by the mean winter maximum

 

The only issue with the formula is that it places the same emphasis on a day with falling sleet as a 10 foot snowdrift surely? 

 

5 days of sleet and no snow = 5 points. 1 day of snow and 10 foot snowdrifts = 2 points

[Weather-history]

Well according to the stats I have just looked at Manchester has recorded 12 days when the min dropped below freezing. The lowest min temps was -5C recorded on the 19th Jan, 2nd Feb. So rather poor if I was honest. My lowest  min in Peterborough is only -4C!

 

Still the 12Z GFS shows why winter may not yet be over.

 

http://www.wetterzentrale.de/pics/Rtavn3841.gif

 

I don't know what stats you have looked at but 26 air frosts here.

 

The only issue with the formula is that it places the same emphasis on a day with falling sleet as a 10 foot snowdrift surely? 

 

5 days of sleet and no snow = 5 points. 1 day of snow and 10 foot snowdrifts = 2 points

When was the last time you saw 10 foot snowdrifts in low lying Manchester?

I think we go off on a tangent here......

[Frosty.]

I've been waiting a long time to say..look east for our weather and the Gfs 12z operational is setting up a peach of a cold spell later in low res with light snow grains / flurries pushing into eastern coastal counties, what a great finale to the meteorological winter that would be. As for the reliable timeframe, an unsettled blip coming up, especially Monday as a band of heavy rain pushes east and in the far north, a brief risk of snow showers as cold air digs in behind, then the Azores high builds in with plenty of sunshine and light winds but cold frosty nights, it could be a prolonged settled spell from next Tuesday onwards.

[Daniel*]

Superb finale.

With much of Europe going into the freezer -20 850s extending to Poland if my geography is correct.

I seriously think winter will not go without a fight. I do feel a 2013 scenario, could be on the cards.

[bluearmy]

The extended eps have played with the trough fi dropping in approaching the end of feb

night great consistency yet but some runs dropping euro heights, more so to our se. This is a fairly similar signal to the last cold trough.

Would like to see this gain consistency and also perhaps some strat support as happened last time.

[Frosty.]

I wonder if Steve murrs chicken will make an appearance this evening although charts like this verifying are as rare as hens teeth. Lordy lordy it's been as quiet as summer in here today, hope the models can change all that before winter is over!!

[snowblizzard]

I wonder if Steve murrs chicken will make an appearance this evening although charts like this verifying are as rare as hens teeth. Lordy lordy it's been as quiet as summer in here today, hope the models can change all that before winter is over!!

I'd say approx 0% chance of that chart verifying Frosty!

[Frosty.]

Once again the Ecm 12z ends with a promising chart for upstream cold potential, nice jet alignment taking shape at T+240 as high pressure pulls westwards and a deepening trough swings SE.

High pressure is set to dominate next week apart from Monday although the far north looks windier,milder and cloudier with drizzly rain as Atlantic weather brushes around the top of the high but most of us should see much brighter weather than we saw today with overnight frosts under clear skies. In the short term, a front moving east on Friday with a band of rain gradually breaking up and temperatures recovering to average on friday and during the weekend, nothing like as cold as it has felt today, another band of persistent rain pushing east on Sunday night and Monday but looking fine for many thereafter.

Edited February 11, 2015 by Frosty.

[ANYWEATHER]

I wonder if Steve murrs chicken will make an appearance this evening although charts like this verifying are as rare as hens teeth. Lordy lordy it's been as quiet as summer in here today, hope the models can change all that before winter is over!!

I expect Steve Murrs chicken has fallen asleep with boredom  A little blip in the settled conditions come Friday, but back to Anticyclonic gloom next week. The gfs charts at the end of there run show a beautifully interesting winter chart. Better save that as a screen saver   What a difference a year makes, last February ,stormy, mild and very wet. This February completely opposite. Only the great British weather can do this....

[Frosty.]

I expect Steve Murrs chicken has fallen asleep with boredom

Well at least a few of us are trying to keep the model output discussion alive!!

Anyway, I see signs of hope for another cold shot from the north beyond T+240.

[kumquat]

Even the mighty NAVGEM has -6 uppers as close as 144

 

What is there not to like?

 

[knocker]

Once again the Ecm 12z ends with a promising chart for upstream cold potential, nice jet alignment taking shape at T+240 as high pressure pulls westwards and a deepening trough swings SE.

 

 

That's true but did you note there is much warm air in that set up with surface temps of plus 9C in England?

[Frosty.]

That's true but did you note there is much warm air in that set up with surface temps of plus 9C in England?

Beyond T+240 the Ecm 12z would turn much colder, shame the run ends at the point it looks most interesting for coldies. I'm hoping we will have another cold shot from the north or even better, our first from the east before the meteorological winter ends in a little over two weeks time.

Edited February 11, 2015 by Frosty.

[polar vortex]

Strong influences from the MJO showing up in the models now with more amplified patterns in the mid range and beyond. 

I have been banging this drum for a few days now of perhaps a MJO related pattern change last third of February. 

Clueless as to whether it would be from the east or north or indeed something in between but IF it does transpire then the 

chances are it could be a very potent affair.  

There is an abundance of deep cold in the Arctic and should a dropping AO send some of that our way then we could

easily still be looking at possible ice days, severe frosts and powder snow.The ECM tonight had it gone on another 48

hours would have covered the country in -10 to -12c uppers at least.

Fun times ahead perhaps.

[Vorticity0123]

Post 11-02

Over the last few days, the UK has seen a dominance of high pressure, resulting in quiet weather. Yet the perception of the weather associated with this high will have been very different over various parts of the UK, with some parts experiencing loads of sunny days and others only seeing low clouds hanging around. A (possible) change in the weather pattern is underway, though, as low pressure starts to become more prevalent near the UK. How will this all pan out? And will high pressure return after a few days? I’ll try to present an answer to these questions in this post.

 

For the first 96 hours, I’ll use GFS charts as a guide.

 

Current situation

 

For the current situation, check the GFS output below:

 

GFS surface level pressure and 500 hPa heights (colours), 12Z run T+0.

 

As can be seen from the image, the UK is under the influence of a 500 hPa ridge (orange colours edging northward) with associated surface high pressure area located over central Europe.

 

However, on closer look, the situation very much resembles an Omega block. The Omega block is indicated by the black line. On the 500 hPa contours, the Omega structure becomes visible when following the 500 hPa contour between the most yellow and the slightly more orange contour (in other words, one gradation of heights higher than the 552 dam line, which is denoted in black). The signature is defined by low pressure (and associated 500 hPa troughing) to the southwest and southeast of the high pressure area over Central Europe. More information about Omega blocks can be found here.

 

Such Omega blocks are usually difficult to break down, and this also explains the temporal extent of the duration of the high pressure are previously located over the UK (as it has shifted eastward with time).

 

Aside from this Omega block, a strong 500 hPa trough can be seen extending over the United States, which has been causing multiple cold outbreaks and snowstorms over that area.

 

Low pressure activity is currently located far to the north of the UK, unable to influence the weather directly.

 

The result of this is weak southerly flow over the UK, bringing rather mild conditions.

 

Short-term outlook

 

24 hours later, the following weather pattern prevails:

 

GFS surface level pressure and 500 hPa heights (colours), 12Z run T+24.

 

The Omega block has shifted even further to the east. More importantly, a low pressure area (associated with a small 500 hPa trough; indicated by blue colours nosing southward) is taking aim at the UK. This low is located about midway between Ireland and Canada.

 

Also, a vigorous low pressure area can be seen off the East Coast of the US, which could cause another round of snowfall along the East Coast.

Another 24 hours later, the low is crossing into the UK, as can be seen below:

 

GFS surface level pressure and 500 hPa heights (colours), 12Z run T+48

 

The high pressure area (and associated 500 hPa ridge) which has been dominating our weather over the past week or so has moved even further eastward, losing its influence over the UK. What is nice to see is that still an Omega signature can be seen, with 500 hPa troughs to the southwest and southeast of the high.

 

Also, there appears to be a tandem of lows at the latitude of the UK, which may be able to bring a sustained period of somewhat more unsettled weather.

 

Another 2 days later (so 4 days from now) there have been some interesting developments:

 

GFS surface level pressure and 500 hPa heights (colours), 12Z run T+96

 

A very deep 500 hPa trough has become established over Greenland, with associated very deep surface low pressure area (down to 950 hPa). Furthermore, another intensifying low is moving just off the East Coast, possibly being another harbinger of snow there.

 

However, the more interesting part comes from the Omega block, which has become fragmented. In fact, the upper ridge has become cut-off toward Scandinavia, creating a surface Scandinavian high. Would this be a precursor to very cold conditions over Western Europe?

 

Unfortunately, the answer to this question is no. This can be seen from the 850 hPa temperatures at the same timeframe:

 

http://www.wetterzentrale.de/pics/Rtavn962.gif

 

What can be seen is that there are no cold 850 hPa temperatures located in the vicinity of the high (with temps generally exceeding 0*C all the way toward Belarus).

 

Mid-term model intercomparison

 

For the mid-term analysis, the ECMWF, UKMET and GFS output (12Z runs) for 6 days for now will be compared

 

http://www.wetterzentrale.de/pics/Rukm1441.gif UKMET

 

http://www.wetterzentrale.de/pics/Recm1441.gif ECMWF

 

http://www.wetterzentrale.de/pics/Rtavn1441.gif GFS

 

All models show new 500 hPa ridging from the Atlantic developing toward the UK, heralding a trend toward renewed high pressure across the UK. Furthermore, the trough to the west of Ireland has shifted even further to the west losing its influence over the UK. Finally, all models also show some kind of troughing (indicated by green colours edging southward) to be located ahead of the ridge somewhere over Central Europe.

 

This trough could bring some cooler air toward the UK, and maybe even snow showers in elevated areas. It could be one to pay attention to if one is looking to some wintry weather. Of course details are hard to pinpoint at such timeframe.

 

However, there is considerable variation regarding the position and depth of this trough, as UKMET shows a much deeper trough than GFS and ECMWF. Furthermore, the ridge over Eastern Europe is handled differently by the models, with the ECMWF shows the strongest and most northerly positioned ridge, while the GFS is somewhat further south and weaker. The UKMET presents a vastly different idea by showing 500 hPa troughing (green colours) in that area.

 

Given that blockades are usually quite difficult to model, there might be some flip-flop about this feature in the coming days, potentially also having some effects at the ridge over Western Europe. This is merely speculation, though.

 

Long-term prospects

 

For the long-term outlook, GFS and ECMWF ensembles for 10 days out will be used first. They are presented below:

 

http://www.wetterzentrale.de/pics/Reem2401.gif ECMWF

 

http://www.wetterzentrale.de/pics/Rtavn2401.gif GFS

 

The ensembles from both ECMWF and GFS show a 500 hPa ridge (orange heights) being located over the UK. These are associated with high pressure at the surface, giving credence to believe that the UK will be experiencing a sustained period of settled weather.

However, there is quite some disagreement about the position of the upper ridge. The ECMWF ensembles have the ridge much further west than the GFS, placing it on average over the central Atlantic. On the other hand, the GFS has it positioned over Western Europe. This will have significant implications on the type of airmass affecting the UK, as well as on possible cloudiness and variation in temperatures.

 

On the other hand, the most low pressure activity is expected to be located well north of the UK.

 

Looking for further evidence, the NOAA 8-14 day outlook agrees with the general pattern sketched above, as can be seen below:

 

NOAA 8-14 day 500 hPa heights (contours) and anomalies (broken lines).

 

What can be seen is that NOAA also expects an upper level ridge to be present  somewhere near the UK (as can be seen from the green lines pointing toward mainland Europe and the red/positive height anomalies. This adds confidence that high pressure will dominate the UK in about 10 days’ time.

 

Teleconnections

 

A different way to make an expectation for the weather for several days out is to look at so-called teleconnections. Teleconnections are an index for climate anomalies which are related to each other. For now, the MJO (Madden Julian Oscillation) and GWO (Global Wind Oscillation) will be discussed.

 

MJO

 

A description of the MJO can be found here.

 

The GEFS Ensemble MJO forecast shows the MJO moving toward Phase 1 after being undefined for a long period of time.

 

GEFS MJO forecast (12Z run). The green line indicates the average forecast.

 

However, looks can be deceiving. Quoting from the Climate Prediction Center:

 

 

The MJO remained weak during the past week. Although some indicators, including the RMM MJO Index, the CPC MJO Index, and the upper-level velocity potential spatial anomaly pattern indicated some eastward propagation of a weak signal over the Western Hemisphere, the global OLR pattern and equatorial zonal wind anomalies are not consistent with robust MJO activity. The tropical convective pattern continues to be strongly influenced by other modes, including Equatorial Rossby Wave (ERW) activity over the western and central Pacific.

 

The full article can be found here.

 

Summarizing: Even though the GEFS is showing MJO activity to develop, the signal is caused by other causes of tropical variability which are not related to the MJO. Therefore, the MJO is not a good guide to base a weather forecast upon for the time being.

 

GWO

 

First, it has to be emphasized that I am by no means an expert on this subject.

 

A good guide for the GWO can be found here. For now, I’ll try to keep it as simple as possible.

Below is a forecast for the GWO over the next couple of days:

GWO forecast from the GEFS model. The forecast is indicated by the green line.

 

What can be seen is that the GWO is currently not well defined. However, in a few days it is expected to emerge in phase 1 and 2.

Phase 1 and 2 are, by a huge simplification, pointing toward some kind of Atlantic amplification. This has also been mentioned in much more detail by Tamara yesterday.

 

Conclusion

 

Although we are coming under the influence of a low pressure area for the next few days, it appears that high pressure will take hold for an extended period of time quickly afterward. This will result in a brief period of unsettled weather being followed by much calmer conditions. It will be interesting to see whether this signal will be becoming more evident over the next few days.

 

EDIT: Interchanged some links for images.

EDIT2: modified GWO part a little

 

Sources:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

https://forum.netweather.tv/topic/52083-gwo-and-global-angular-momentum/

http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

http://www.wetterzentrale.de/topkarten/fsavneur.html

https://ohwxramblings.files.wordpress.com/2012/11/gwo-maps.png

http://www.theweatherprediction.com/habyhints/144/

http://en.wikipedia.org/wiki/Teleconnection

Edited February 12, 2015 by Vorticity0123

[Milhouse]

Temperatures rising into double figures under high pressure. In any sunny spells it would feel rather pleasant.

 

[Captain Shortwave]

Whilst everyone is searching in deep FI for cold weather. No one spotted this hilarious gem from the GEM (do not take seriously but still).

Watch the cold pool over Eastern Europe....

It migrates westwards towards the UK

Pretty potent little beauty

 

Fun times 

[Cloud 10]

Whilst everyone is searching in deep FI for cold weather. No one spotted this hilarious gem from the GEM (do not take seriously but still).

 

Watch the cold pool over Eastern Europe....

 

 

 

 

Fun times 

 

The GEM control run is "at it" again in deepest darkest FI.

 

[bluearmy]

Actually, it was also there on the 00z run captain.

The GEM probably picks out something in fi against the odds about five times a year. Can't see this being one of them though!

[West is Best]

I've been waiting a long time to say..look east for our weather and the Gfs 12z operational is setting up a peach of a cold spell later

 

With the emphasis on the word 'later'. That's T360. I mean, I know we're all desperately rooting around for something before official end of winter 17 days from now but T300+ is pushing our luck somewhat?!

 

Still time for another cold snap before we're through. We've had two here: one between Christmas and New Year and the other the one beginning of Feb. Both produced a sprinkle of snow and some frosts. Better than last year, for sure. A third would complete the sequence.

Edited February 11, 2015 by West is Best