In Depth Model Discussion, Analysis and Summaries

[Glacier Point]

Interesting...

Asian torques are joining in the act...

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltaum.90day.gif

Mountain torques to spike in the next few days. Easterly winds are also decreasing across the tropics.

Tendency in relative angular momentum is well up and the GWO locked firmly in phase 4:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltend.sig.90day.gif

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

That's a significant westerly wind pulse across the tropics. These generally work their way poleward over time so some potential warm air advection likely in the next 10-14 days. The negative wind anomaly across the high latitudes is still weak, so no blocking signal just yet. Just yet. However, I may have to review that mild February call on the back of the data in front of us.

[phil nw.]

Interesting...

Asian torques are joining in the act...

http://www.esrl.noaa...ltaum.90day.gif

Mountain torques to spike in the next few days. Easterly winds are also decreasing across the tropics.

Tendency in relative angular momentum is well up and the GWO locked firmly in phase 4:

http://www.esrl.noaa...d.sig.90day.gif

http://www.esrl.noaa...gcm/gwo_40d.gif

That's a significant westerly wind pulse across the tropics. These generally work their way poleward over time so some potential warm air advection likely in the next 10-14 days. The negative wind anomaly across the high latitudes is still weak, so no blocking signal just yet. Just yet. However, I may have to review that mild February call on the back of the data in front of us.

Thanks again Stewart.

It`s certainly a fluid picture at the moment and i think we all appreciate you updating us.

I don`t know if the 12z output would take your latest obs. into account but the Ens. look cold.

[BLAST FROM THE PAST]

Interesting...

Asian torques are joining in the act...

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltaum.90day.gif

Mountain torques to spike in the next few days. Easterly winds are also decreasing across the tropics.

Tendency in relative angular momentum is well up and the GWO locked firmly in phase 4:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltend.sig.90day.gif

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

That's a significant westerly wind pulse across the tropics. These generally work their way poleward over time so some potential warm air advection likely in the next 10-14 days. The negative wind anomaly across the high latitudes is still weak, so no blocking signal just yet. Just yet. However, I may have to review that mild February call on the back of the data in front of us.

Ah Stew, the addition I was looking for. You know that I have been calling for a cold Feb now for a week to 10days and reading your earlier analysis I was going to suggest that when this block to W then NW develops it willgo nowhere until midmonth gradually transferring to Scandi. So Beginning Feb we will be dominated by NW'ly, N'ly, Ne'ly winds with increasing Ne'ly to E'ly as we hit midmonth on. The signal from the solar side of things is for a very weak/non existent northern arm of the jet in Feb with energy kicking south...your post above really interests me now and certainly supports my viewpoint. Time will but for me watch how the collapse of the northerly in FI and the PV over Greenland disintegrates as we get towards end of the week.

BFTP

Edited January 24, 2010 by BLAST FROM THE PAST

[Thundery wintry showers]

I'd be happy to see synoptics similiar to Feb 73 and 99, perhaps bringing a colder feed than those two monts, polar maritime air was frequent with pulses of arctic maritime air at times bringing snow showers to many north western northern and north eastern parts, I'd prefer the polar air to be in greater residency though than tropical maritime air.

From a personal preference perspective I agree, and a good match with the pattern you describe would be February 1970, which had frequent northerly and north-westerly winds and just occasional anticyclonic/tropical maritime interludes. As well as being quite a snowy month, some parts of the country had their sunniest February of the century.

A February 1970 style month looks an outside bet at this stage but maybe if we gain a stronger negative wind anomaly over the pole and warm air advection up the west of Greenland then it could happen.

[kold weather]

I'm also a little more curious tonight given the output BFTP/GP and the broad signals that are being picked up. For now the start of Feb looks like having a mean upper high maybe just to our west however IF we can get the PV forming a little further west over Canada then the upper high is in the perfect location to bring down quite a potent northerly flow again at some point in the first 10 days, equally though a flatter pattern could just as easily lead to a very mild flow around the HP if it ends up to our SW/S instead.

So IMO two possible evolutions to cold given the general region where the upper high will be and also the constant attempts at an upper trough feature digging down towards Europe and thats either the HP gets far enough NE to give inversion/ESE type airflow, or for the PV to be far enough west that when LP's do run up the east coast of the USA the high is far enough west to shunt colder air into our path.

I'll throw into the equation the simple idea that the models have been too far south with upper high features this winter thus far, so I'm fully expect the high to end up probably at a similar latitude to the UK rather then being focused to our SW like quite a lot of the models are still suggesting.

[cooling climate]

Reading over the posts regarding the teleconnections, I gather that we could be in for a February similar to the likes of 1973 and 1999? That's certainly what the current pattern reminds me of, in conjunction with the signals for HP to the south and west and trough over Scandinavia. Both of those Februarys had alternation between mild anticyclonic westerly types and cold northerly types, and came out mild overall but with many areas having close to average snow amounts.

I think something like that, if it comes off, would be a minor victory for cold/snow lovers as there has always been the real possibility of a very mild snowless February.

Can not see this at all I think you are completely underestimating the amount of northern blocking and -AO, - NAO

that will prevail in February.

February is likely imo to be very much colder than the years you have mentioned I think.

[Glacier Point]

A westerly wind burst is clearly underway in the tropics right now. This one centred around the Dateline, the most west since September...

The MJO is centred in phase 7 and, with this wind profile, there's no reason why that it shouldn't progress through phase 8 in due course. Phase 8 teleconnects to a mid Atlantic ridge:

http://raleighwx.easternuswx.com/MJO/FebruaryPhase8500mb.gif

This is more or less consistent with GFS ensemble mean guidance in the 11-15 day timeframe:

http://raleighwx.easternuswx.com/models/gfsensemble/12zENS11-15day500mbHeightAnomalyNH.gif

In terms of the more important GWO, currently in phase 4 - 5 transition due to prolonged westerly mountain torque adding westerlies to the atmosphere.

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

Relative angular momentum is now rising and the general trend seems to be for easterlies to decrease over the tropics. This should allow angular momentum to continue to edge up, repeating the evolution in December towards phase 5:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig.90day.gif

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_90d.gif

As mentioned yesterday, the polar profile is not favourable to blocking over Greenland in contrast to December.

Interestingly, phase 5 of the GWO teleconnects to the mean trough to our east to shift slightly westwards:

That would mean the UK being kept in a north-westerly flow with the mean mid Atlantic ridge further west. This is a mean position, so energy spilling over the top will tend to wobble the high back and forward. That is unlikely to support any notion of temperatures breaking above average for the first 10 days of Feb.

[bluearmy]

given the progressive nature of the op runs beyond T168 today and yesterday, i am reassured to see this mean anomoly days 8/14

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

of course, as you mentioned, these outputs are mean representations and daily variations can be marked

[LomondSnowstorm]

Thanks for the update GP. Looks good for some cold zonality early month then, with hopefully a good chance of snow for those of us north of Berwick!

LS

[Glacier Point]

Both GWO and MJO plots indicate that the atmosphere is in a similar position to where it was in mid December, immediately prior to the cold outbreak.

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_90d.gif

http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.html

MJO forecasts continue to advertise a phase 7/8 evolution which teleconnects to a block centred south of Greenland:

http://www.cpc.ncep.noaa.gov/products/people/wd52qz/mjoindex/index/diagram_40days_forecastGFSOP_CFSOP_GEFS.gif

http://raleighwx.easternuswx.com/MJO/JanuaryPhase7500mb.gif

http://raleighwx.easternuswx.com/MJO/FebruaryPhase8500mb.gif

Tendency in relative angular momentum is still upward although mountain torques have just started to fall. I suspect we will continue to see a neutral / positive torque persist for a few more days whilst the upward trend will likely favour a phase 5 evolution of the GWO before an orbit similar to the period around 20th December.

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig.90day.gif

This loosely translates to the trough over Scandinavia edging westwards before filling and height rises to the west or NW, so the GWO and MJO sending similar signals.

Tonight's CPC 8-10 day outlook is rock solid behind this:

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

A feature of the modelling is the trend for a substantive blocking signal to emerge in the extended timeframe. Zonal wind anomalies are becoming favourable for development of these structures:

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_UGRD_ANOM_JFM_NH_2010.gif

Whether the negative zonal wind anomalies associated with the recent warming propagate over time will be an ongoing monitoring issue. Currently the negative zonal wind anomalies are centred at 10hPa level, still high up in the stratosphere.

Without doubt, February continues to look like maintaining the much below average trend of the winter.

[Snowyowl9]

Sounds like christmas is coming back going by that very interesting post.

http://www.wetterzentrale.de/archive/ra/2009/Rrea00120091220.gif

Edited January 26, 2010 by Snowyowl9

[chionomaniac]

It is great to see things setting up so nicely GP, with the onset of February so close. February was always a wild card scenario and it looks like the MMW has just played the joker for the cold side. I know that I have mentioned previously how there can be an initial downburst phase of propagation following vortex disruption but even I am surprised at how unsuccessful the recent cooling of the stratosphere has been in sustaining a strong PV. I suspect that the PV will take some time at regaining any kind of strength and this winter pattern to continue. How cooperative is it of the stratospheric vortex to push a trough towards Scandi just as the tropical convection forcing reaches MJO phases 7/8!!!? Normally in winters gone by these teleconnections are at odds with each other. Hopefully now we can see a return to blocking that the models are teasing us with.

c

[lorenzo]

Yes I have a suspicion we could be in for a cold spell towards the end of the month. Stratospheric vorticity charts indicate a strong signal for high pressure towards the med and a weekening signal for high pressure towards russia.

I notice how 8 days out the signal for that russian high has disappeared or gone south which is not well depicted in the forecasts at the moment. I think this is a historical bias coming out in the models. Unfortunately the icelandic low is still present. So for the next eight days at least we can expect some rather unsettled conditions.

After that the stratospheric vortex displacement begins to move a bit more eastwards at lower levels.

This leaves me with the idea that we could see a blocked atlantic pattern at around 13 days out especially if we are into MJO Phase 7 or 8. For once I think the old adage that what weather new york has we will see a week later might be true.

Looking back through the thread this post stood out in regards to the current position on the models..

[weatherjunkie]

This should probably go into the other model thread, but I thought some would enjoy it with all the talk of going back into the icebox.

18z GEFS NAO Outlook

12z similar but not as robust around the 2/6-2/12 time period. It gets as high as -0.4 SD around the 3rd and then dips to around -2.25 SD on the 10th.

Edited January 28, 2010 by weatherjunkie

[Nick F]

Dare I say it, I think we are almost into a win-win situation for cold in the longer-term outlook for February, certainly the first half. I have been keeping an eye on the forecasted H500 anomalies for the northern hemisphere for the last week, and with each day, particularly the last few days, there has been growing support for a significant +ve height anomaly towards and over the Barents Sea, shown by the 12z ECM/GFS 8-10 day mean H500 comparisons:

... and with time, this spreading westwards across Greenland, as shown by the NOAA CPC prognostic 6-10 day and 8-14 day H500s:

AO going -ve and NAO showing signs of nose-diving too:

What’s causing the major warming of the mid-upper levels of the troposphere in Northern latitudes, well you can clearly see (below) a down-welling of +ve temperature anomalies from the stratosphere – helping build those heights over Barents and Greenland. This looks a rather large and substantial anomaly above the troposphere, so the down-welling +ve temp anomalies could last some time with the block perhaps hanging around for quite a while during Feb.

I'm no expert on NH teleconnections, so would be interesting to see what GP or others have to say wrt to any over-riding signals upstream, or whether the position of the high latitude blocking indicated may become favourable or less favourable for the UK.

[Glacier Point]

Models providing extremely poor guidance at the moment, most probably related to changes in the upper atmosphere and how fast warming propagetes down. The time scales for this are not well defined so no suprise that blocking appears, disappears and reappeares. Current data identifies the extent of close any downwelling wave at 150 hPa which is still high above the 200 - 500 hPa layer where this would manifest as tropospheric blocking.

http://www.cpc.ncep....JFM_NH_2010.gif

It should be remembered that we have still a legacy of declining angular momentum through January persisting in the extratropical atmosphere. I think it would be safe to allow for minimum 14-28 days to see the impacts of the warming of the stratosphere work through. That places us into mid February before realistically expecting any heights raised by the warming event. In my view, the models have been way to progressive and failed to cope with this aspect.

The global wind oscillation has provided the most reliable guidance in the medium term evolution, consistently flagging the persistence of the Scandinavian trough.

Currently in phase 5 (Scandinavian trough):

http://www.esrl.noaa...gcm/gwo_40d.gif

The tropical atmosphere looks like stalling with MJO forecasts suggesting a slow, very slow progression through phases 7/8 taking us up to mid month, aided by a westerly wind burst:

http://www.cpc.ncep...._CFSOP_GEFS.gif

Torques are suggested as being close to neutral in the medium term which will keep the GWO in low amplitude orbit through phases 5-6-7-8. Composites for these phases are a bit inconclusive but for the record, as follows:

Phase 5

Phase 6

Phase 7

Phase 8

There is just a hint that easterly winds are stirring across the tropics which will help lower angular momentum in the longer term. With the MJO moving through phase 1 into 2 this may well signal falling tendency in relative angular momentum towards the Nina base state during the second half of the month. This is signal for ridge over the UK.

Before that, the GWO composites suggest the potential for trough disruption in the Atlantic and retrogression of highs to the North, as well as ridges pusing into the UK from the south-west (as per previous posting). A trough (or possible cut off upper low) to our east continues to look probable, as does some attempt for colder air to establish in from the NE during the second week of Feb.

So pressure building in from the south-west and slow evolution (mild to start) towards heights building across our north then north west delivering a cold snap looks the favourite before a return to high pressure over the UK towards mid month. The evolution thereafter will be dictated by the location of any height rises forced by the stratospheric warming. My best guess would be towards Canada and western Greenland associated with a -NAO pattern altough very low confidence attached to this solution, mainly due to weak guidance from GWO composites and the very uncertain nature of downwelling impacts from the warming stratosphere.

I set out in the winter forecast the uncertainty surrounding February's pattern. That continues to be the case, even on the eve of the new month.

Edited January 30, 2010 by Glacier Point

[BLAST FROM THE PAST]

I set out in the winter forecast the uncertainty surrounding February's pattern. That continues to be the case, even on the eve of the new month.

A weird month for sure Stew, and yes even now very difficult to call.

BFTP

[Glacier Point]

Anomalously warm air is continuing to propogate downwards over the Arctic out of the lower stratosphere. As per latest update, the warmer air has made it to the upper troposphere:

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_JFM_NH_2010.gif

In a beautiful symmetry, westerly wind bursts have continued over the tropics and torques and eddies are helping to transport anomalously strong westerly zonal winds into the extra-tropics whilst neagtive zonal wind anomalies persist across the high latitudes. Mountain and frictional torques are joining in, helping to ramp up tendency in angular momentum.

This has driven the GWO into probable high orbit phase 5:

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

The MJO is moving slowly towards phase 8:

http://www.cpc.ncep.noaa.gov/products/people/wd52qz/mjoindex/index/diagram_40days_forecastGFSOP_CFSOP_GEFS.gif

Composites for these phases:

http://raleighwx.easternuswx.com/MJO/FebruaryPhase8500mb.gif

Good continuity with model developments in the last 24 hours showing a colder pattern mid month.

Thereafter, and subject to a huge amount of uncertainty, the position of high stratospheric ozone concentrations tend to suggest the development of a strong -NAO block centred western Greenland into Canada. This would be logical given a easterly winds forcing the block eastwards.

Phase 6 GWO composites suggest either a mid Atlantic block or height anomalies over southern Greenland, the latter being a more logical evolution given the upper atmosphere profile.

And then ? Falling angular momentum tied into the MJO moving towards phase 1 and removal of westerlies from the atmosphere are likely to result in a mid Atlantic ridge becoming gradually shifted back towards the UK.

A colder pattern is more probable in the medium term. How cold and how long ? Phase 5 and 6 GWO composites would feasibly allow Arctic air to filter into the UK from the NE. However, as the block moves further west, this likely opens up the door for an attack from the south-west. A snowy breakdown potentially.

So to summarise, reasonable chance of some blocking structure developing (but see earlier caveats about the reliance on stratospheric forecasts and timing issues therein). Block to migrate westwards allowing milder air to attempt to work in from the SW.

[Cal]

Thanks GP, one last bite at the cherry?

[chionomaniac]

Thanks for the update GP. I see that the warming at 10 hPa has a little bit left in the tank which is good given the current progress of propagation. It does look like the models are coming together now with this type of scenario. let's hope there are no flies in the ointment this time!

[Glacier Point]

... just to tag onto that update...there should be very low confidence attached at the moment.

Compared to the same juncture mid December, then there was high confidence in the predicted outcome. This time round I can see a lot of potential pitfalls which a colder pattern must negotiate:

1) if and when propogating zonal wind anomalies impact the troposphere;

2) tendencies in angular momentum to remain upward for long enough to prevent the GWO orbiting back through phases 7/8 too soon;

3) tendencies in mountain and frictional torques to keep the GWO in high amplitude rather than lower amplitude which would give a much lower amplitude and therefore quicker phase 6-7-8 transition.

So this should temper any enthusiasm in colder solutions offered by models, not least ones which are prolonged.

[johnholmes]

I suspect Stewart that your original first class prediction for this winter so far may well end up correct for February as well?

The odd short cold spell but nothing prolonged as occurred in December and January I would suggest?

Maybe a coldish spring and early summer which would not be too popular I suspect apart from the usual cold lovers.

[karyo]

I suspect Stewart that your original first class prediction for this winter so far may well end up correct for February as well?

The odd short cold spell but nothing prolonged as occurred in December and January I would suggest?

Maybe a coldish spring and early summer which would not be too popular I suspect apart from the usual cold lovers.

If we get a west based -NAO and a ridge over the continent, as GP mentions, then a mild rainfest from the southwest is likely for February!

Mind you, your last sentence brought a smile to my face!

Karyo

[Glacier Point]

Big, big surge in angular momentum going on right now that really does red flag blocking somewhere in the North Atlantic sector. The key question, where?

Relative angular momentum is well up:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/glaam.sig1-21.90day.gif

Note the negative (blue) anomaly across the high latitudes indicative of blocking signal emerging.

The tendency in relative angular momentum plot shows nicely how this surge has developed over the tropics and moved poleward:

http://www.esrl.noaa.gov/psd/map/images/reanalysis/aam_total/gltend.sig.90day.gif

The GWO is now showing a high amplitude phase 4/5 transition:

http://www.esrl.noaa.gov/psd/map/images/gcm/gwo_40d.gif

These make a phase 5-6 evolution now very likely in the medium term. This teleconnects to a big low in the western Atlantic and blocking centred somewhere between Canada and Greenland, possibly a little further south and east of this position through phase 6 before a break-away ridge sets up over the mid Atlantic towards the UK. A trough solution for the UK through phases 5-6 is also likely. Operational and ensemble mean guidance might not be picking this signal up well enough at the moment.

Model guidance is however trending towards the west based -NAO, but the window for a cold snap month (with cold air being brought in from the NE) is there.

[NL]

Well appreciated GP for your analysis of the teleconnections...mmmm Northeasterly, i like the sound of that.....