Model discussion highlights

[AO-]

Good Morning all,

Despite some promising signals earlier and an outrageous GEM (let alone one Member of its EPS), there are no signs for anything cold in the corrected output of EC this morning. Bit disappointing though. Chances of frost, but that is all. This implies a high chance of a Euro high rather than a Scandinavian block in januari as the best possibility. The chances of southwesterlies is still the highest. Fortunately it is not very wet. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017561

[StretfordEnd1996]

These temperatures next week will feel balmy 

 

But as HP has more of an influence, it may not be a full week of mild-fest temperatures than it may initially seem - cooler at night in less than a weeks time 



Sat 27th dawn - frosty morning potentially



 

That's thanks to this build of HP over the country



So Sun-Thurs, very mild and wet no doubt. Back end of next week it settles down and with that comes more average temperatures. 

It goes to show how HP can often present uppers with contrasting ground temps - at least for a time .. this example (into FI now admittedly) 



Same chart ground temps 


Where does the HP go from here, one may ask.

Who knows.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017723

[sebastiaan1973]

Very interesting, I share iot here too, because it is important for understanding the models.   

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD023359

 Simon Lee writes in a tweet about this article. If we have a reflective type of SSW (Judah Cohen states the same), this leads to a Pacific blocking and westerlies over the N-A

Abstract

Sudden stratospheric warming (SSW) events have received increased attention since their impacts on the troposphere became evident recently. Studies of SSW usually focus on polar stratospheric conditions; however, understanding the global impact of these events requires studying them from a wider perspective. Case studies are used to clarify the characteristics of the stratosphere-troposphere dynamical coupling, and the meridional extent of the phenomena associated with SSW. Results show that differences in the recovery phase can be used to classify SSW events into two types. The first is the absorbing type of SSW, which has a longer timescale as well as a larger meridional extent due to the persistent incoming planetary waves from the troposphere. The absorbing type of SSW is related to the annular mode on the surface through poleward and downward migration of the deceleration region of the polar night jet. The other is the reflecting type. This is characterized by a quick termination of the warming episode due to the reflection of planetary waves in the stratosphere, which leads to an amplification of tropospheric planetary waves inducing strong westerlies over the North Atlantic and blocking over the North Pacific sector. Differences in the tropospheric impact of the absorbing and reflecting SSWs are also confirmed with composite analysis of 22 major SSWs.

Key Points

New classification of sudden stratospheric warming during the recovery phase

Absorbing type warming events induce Arctic Oscillation on the surface

Reflecting-type warming events produce a Pacific blocking

Edit. I place the tropospheric setting after Absorbing & Reflecting. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017833

[Eagle Eye]

20 minutes ago, Met4Cast said:

This isn’t your typical SSW bringing down a strong vortex with big surface impacts. We already have a weak vortex & have done for most of winter, this SSW as a result is a bit like adding a glass of water to an ocean and expecting a big change. 

Despite the warming on the 16th being technically a major SSW, we’ve already seen a typical SSW response (current cold) from the previous minor event. 

In fact, there have now been 3 warming events this season! 

Strong vortex’s fall hard.. a weak vortex being punched doesn’t. A quick return to average strength in the next couple of weeks is now very likely, we’ve lost the tropospheric “punching”. 

Agreed, in fact the lack of a significant EHF response that occurs long after a proper SSWE shows that. Normally you have - VE EHF lasting 40 days post ssw, peaking at day 10-15. This - VE EHF response is sort of a sharp yet weak looking return to the Strat state peaking around what, day 5-7 ish? Before surface forcing can take over again. 

 

 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017913

[jules216]

6 hours ago, bluearmy said:

You’d expect any response likely within the next two weeks to now be picked up by the models (especially eps ) as the warmings of the past three weeks are pretty much done 

nothing solid showing yet although the scandi ridge solution is the most common departure from the norm that we are seeing play out 

@jules216 - I think you’re in a decent  location for weeks 2 and 3. Either a cold trough or a good chance of a hit from a deep cold pool 

There is a hint of easterlies on the GEFS but I need to see more traction elsewhere. There is reasonable presumption that this time around the route to cold if.it materializes will come from the east and at least not west based -NAO threat. Also with where high pressure is situated in the begining we wont have to endure endless rain before that. In november and december the very wet precursor pattern leading Up to first snap meant that ground was not enough deep Frozen and even 12cm fall next day settled in to 6-7cm and first hint of +1 managed to thaw Snow in a day. This is very important here. Imagine past 7-10 days there was Tmin every night around -9/-11 and soil like a rock, then Yesterday 4cm fell and even after 20hr today of +1/+2 and 5mm rain from 4cm 2cm survived. Wish this would have Been precursor on 25.11 but it was too early in season for solid soil freeze. Picture today earlier which is not pretty,but its shows how durable this 4cm fall Yesterday is proving to be.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018329

[Mike Poole]

All hell’s broken loose on the extended clusters, T264+:

It’s like the model’s got wind of something .

Even on clusters 4 and 5, which continue the +NAO regime, there are blocking attempts, but they don’t take hold.

Clusters 1 and 6 build a Scandi high, I imagine the different members will mean different outcomes for the UK here, but the general pattern is what is important this far out.

Clusters 2 and 3 show retrogression towards Greenland.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018480

[jules216]

There was a lot of wibe around the seasonal forecasts of "back loaded winter" perhaps they meant 20-28.02.2024 period. As currently there is a big overwhelming signal of very mild Europe in next 3 weeks. Currently the best and only really coolish and snowy period date here in central Europe is 25.11-10.12. Which is as front loaded as it gets. The clusters 240-364 on EPS are showing what would be almost a record breaking warmth being summer time. This winter is a very good match of a blend of last 2. Few december promises and almost snowless January,followed by a week of cold in February and then the really cold pattern sets in spring time. This is almost happening every single year since 2017. This trend shouldnt be ignored. As I ve seen very little re-analysis after the wibe ends ",what has gone wrong". My oponion is that its a blend of factors. 1. Haddley Cell expansion - high pressure from north Africa as legacy of hot summers - pushing north creating a wall that prevents cold air to push too much south, and SST once they cool enough its spring when cold synooptics kick in, Late March - April. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5017662

[Singularity]

27 minutes ago, pages said:

 

I want cold and snow as much as anyone my young son constantly asking when is it going to snow enough to go on sledge.

But I just can't see us getting opportunity for at least 3 weeks.

I know MJO forecast is just that but it's not trending in a good direction.

A few days back ECM and GFS both had MJO reaching phase 7 at decent amplitude.

Now ECM has it barely reaching for phase 7 and heading for COD and GFS looks even worse diving into the COD from phase 6 and looking like it's going to cycle back to phase 5. 

 

 

 

 

Ah but here’s the thing - once you’re into Feb, with an El Niño-like (high AAM) background such as is expected next month, the Scandi high signal emerges with MJO phase 6, with 7 becoming the transitional one that’s part Scandi high, part -NAO.

So if the models lock onto predicting it to be slow moving in phase 6, I won’t be concerned about all this talk of highs to our N/NE being for nowt.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018546

[Catacol]

And so the cold snap ends. Snap rather than a spell - 9/10 for the depth and quality of the cold (I loved the frost free dry cold and then the intense frost that broke the fuel flap on my car!) and I daresay 9/10 for many in Scotland or parts of the NW who love snow. The NW probably viewed a scandy trough dropping in with a sense of "been here before" - and then low and behold the trough developed a curious westerly and many parts cashed in. The wonderful variability of the weather. But the overall 9/10 has to lose 3 points for the shorter than expected duration, and then a further point for the failed channel runner and anything for the south. Those in the east (like me) would probably knock a further 1 off for the absence of any north sea activity. Lands as a sort of 4 or 5/10 for me.

We have been unlucky with events in the strat this season, no doubt about that. First the SSW that failed at the start of the month that could have done much to cement a cold month (and was probably a key factor in suggestions from the MetO) and then a second warming that split the vortex but has turned into a reflection type of warming, where wave forcing bounces off the strat back towards the trop and helps reinforce default westerlies. Laid out nicely in Amy Butler's recent blog. And frankly a frustration....but one we have to live with. Coincides with IO MJO phases and the lagged impacts the elastic band of AAM being at the wrong end of the "ping" have ensured. Hey presto - cold out very fast, violently mobile atlantic arrives. The weather may be chaotic, but it is also broadly predictable once drivers lock in.

And that broad predictability is what lends significant wintry optimism going forward. First of all, the ebb and blow of momentum that is the GWO.

Look at the patterns here. Note that prior to our December snap and again prior to our January snap we saw a rising orbit take hold. This graphical representation of global windflows gives a strong indication as to whether the atmosphere is predisposed to encourage blocking, and to see the next orbit kick in we need a rising momentum profile.

And here it is. This has been sluggish - I thought the gun had been fired a few days ago...but it appears now that 16 Jan was the moment we hit the starting button. Frictional torque distinctly positive

Mountain torque generally positive also

and this produces the awaited beginning of the next surge in momentum illustrated by a positive tendency now in play

This will accelerate, not least because the MJO is coming back to where snow lovers want it - phases 6/7/8/1 broadly speaking

So. We watch and wait with anticipation given GLAAM has remained positive overall and we are in a back loaded Nino context. The atlantic will fizz for the 5 days or so I have flagged before as the likely window, and then we will gradually see the effects of the forcings listed above impact on NWP. There are signs already, as expected catching the eye around 26/27/28 Jan. Note ridging towards Scandy on the EPS for the end of the week

quite pronounced by the end of the weekend

Someone earlier said there was little sign of such developments, and used GEFS 850s as the tool to evidence it. Worst possible source of evidence for extended forecasting possible. Don't get swayed by such stuff.

Disappointing to see the intense cold depart so soon, frustrating that the strat has refused to play ball so far, but winter a long way from done and the mild I suspect will be an interlude rather than a pattern starter. I still see February as blocked and have faith in the recent Glosea, JMA, CMC and other long range models that see a -AO overall. Plenty of time still to roll those dice again and get lucky.

 

 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018653

[Nick F]

8 minutes ago, Mike Poole said:

T264+:

Cluster 1 holds the Scandi block in a good position, cluster 2 collapses back to +NAO, clusters 3 and 4 risk ending up with a UK high.  This might retrogress on cluster 3 beyond the timeframe.  

None of the extended clusters showing Atlantic troughing / upper flow energy undercutting high pressure building north over Europe that would hold a Scandi high in place for a sustained enough period to bring cold air our way though, so the high would eventually collapse. My worry is the lack of low heights especially over Iberia from Atlantic troughing undercutting, as well as further east over the Mediterranean Basin from undercutting of cold air from the NE, will mean we end up with a large Scandi-Euro High of little benefit to coldies in the UK other than some surface cold perhaps.

But, we know these clusters can change, so more runs needed. But I'd feel much happier if we saw troughing extending from the Atlantic over Iberia rather than the semi-permanent Azores ridging there. Extremely dry across parts of southern and eastern Spain this winter so far, due to lack troughing extending from the Atlantic over Iberia with ridging dominating.

We can get away with cold air undercutting high pressure over Scandinavia from the NE into southern Europe to lower heights over the central Med to bring a brief cold easterly, but prefer of the Atlantic troughing undercuts too to make it more sustained.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018826

[johnholmes]

Friday 19 January

The return to milder air was well signed by NOAA from last Thur/Fri.

NOAA 6-10 shows strong SW’ly into UK with some ridging over Scandinavia whilst the +ve height is shown off ne coast of Spain around 240DM. In the far west it shows a ridge-trough set up (will this affect the UK area with time?) 180 DM in the ridge, east of the trough a stron WNW flow to beneath the main trough in its usual area and thence into the UK etc

The 8-14 keeps the ridge off W Alaska but ‘loses’ the trough with only the main trough, simllar to the 6-10 into the ridge east of the UK, so a very similar pattern in the UK area.

Turning to ECMWF, which never went for as much ridging nor quite as low 850’s as other models suggested and it maintains a most south of west strongish flow through its 5 days (25-29 Jan) with, at the surface, a ridge being more dominant than any low feature. This ridge is moved from Spain to central Europe in the same period. *50 MB temperatures ebb and flo a little at first but overall a rise is show and by the 29 th the whole UK is show > than zero with England and  Wales above 5 C

UK Met for 23-25 Jan has a fairly stron broad westerly with minor ridges and troughs running through. This shows on the surface as two deep lows that track in a general easterly direction just north of Scotland.

Overall the flow is a mix of Polar returning maritime air with brief intrusions of Tropical Maritime for more southern areas. Probably some snow on the cold side of passing lows for the Scottish mountains with temperatures fluctuating around normal for most areas.

Climate Prediction Center - 8-14 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5018881

[Singularity]

I find it helps to set skepticism of runs about as high as it can go when looking at a period of potential Scandinavian high development 7+ days away.

Even these days, it remains a weak point for the NWP models; something they really struggle to resolve much in advance. Mainly because of the difficulties resolving the relatively small scale irregularities involved in trough disruption, which is the primary means to get low heights in place over S Europe.

This view can even be applied to entire ensemble sets, owing to their forced perturbation only being at the very start; it does little to help resolve the possible development of new small scale features a week or more away.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019068

[Mike Poole]

I think we may get a heads up on this one from the MJO analysis, because looking at today’s:

Ignoring what the model is predicting, we are right now going into phase 5 at high amplitude.  If that amplitude is maintained, where the models have it decreasing, as we go through phase 5, then I’d be a little more confident it wasn’t going to collapse on us the moment it reaches the ‘good’ phases.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019183

[WYorksWeather]

Going to do my usual post on ensembles etc. later on. But first I'd like to do a more detailed explainer on influences on temperature. In the UK we have two main influences on our temperature that vary depending on the time of year.

The first and most obvious one is solar energy. This one is pretty straightforward. As we move on from the winter solstice, the strength of the sun increases. This process is not linear - initially the change is very slow. At my location, days have lengthened by around 45 minutes since the winter solstice. Of course the peak angle of the sun above the horizon, and hence its strength, has also increased slightly.

We're about four weeks out from the solstice. If we look at where we'll be in another four weeks, so by mid-February, day length will have increased by another 65 minutes. Four weeks after that, by mid-March, the four-weekly increase compared to mid-February is 120 minutes.

Naturally, this process leads a lot of people to think that winter is on its way out by mid-February. However, the second major factor is the temperature of the oceans. Oceans hold an enormous amount of heat, and so they have significant thermal inertia. In other words, sea surface temperatures are at their coldest in March, as they are still responding to colder weather. The same is true over the summer - peak sea surface temperatures in the Northern Hemisphere are typically reached in September.

You can see this clearly in the charts below.  The first chart shows Northern Hemisphere sea surface temperatures today, and the second chart is the projection at day 15. You can still see the advance of the colder colours down the chart, albeit slower than earlier in the winter.

So, how does the change in the sign of temperature work? The answer is that at this time of year we have two competing forces. Sea surface temperatures are still dropping slowly, and solar insolation is increasing slowly. These forces are currently roughly balanced, and hence January and February are relatively similar in temperature.

Towards the middle of February, you see the mean temperature curve begin to bend upwards, and then more sharply in early March. It is at this point that sea surface temperatures are bottoming out, so that counteracting force disappears, and solar insolation begins a more rapid climb.

Summary

Overall, the main point to make is that early to mid-February is still the heart of winter. The four week period from e.g. December 22nd to 19th January probably has a similar, or even slightly lower chance of producing a major cold spell, compared to the upcoming four week period from today, the 19th January, to 16th February.

Beyond that, while severe cold in late February or early March is not unheard of in recent years, most notably the BFTE in 2018, it does become less likely. That following four-week period, from 17th February to 16th March, is a period of much more rapid change.

So, my take on this is that we continue to observe the modelling through to mid-February. If we get to mid-February and there is no evidence of an upcoming cold spell, then only at that stage is the clock running out on winter.

For more experienced posters on here, probably very little of this is new, but I thought it was worth a more detailed explanation.

 

 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019270

[Cambrian]

A confounding feature of this winter so far has been the extent of the tropospheric forcing and the spiritless stratosphere. It’s also been a winter of quite violent bursts of mobility followed by profound periods of stasis, typically signalled by an initial phase of retrogression.

For the former, we have storm Isha and its followers for the coming week, and for the latter, it’s a waiting game. 

Out in week 2 with the 12z GEM ensemble mean what we’re really looking at is a splitting of the southern European heights, one pulse north into Scandinavia, but it’s all very longitudinal and has little traction for an easterly due to the lack of a proper clear out from the south, and ultimately little staying power over Scandinavia. 

 

The other slightly later pulse of heights is west from the Mediterranean into the Atlantic, its passage assisting in scuppering any potential easterly flow through Western Europe, but ultimately this retrogression leads to the prospect of an Atlantic ridge. Notice that the heights in Europe are slowly falling away. 

Looking north, I like the look of the way the PV is being handled, drawn first north away from eastern Canada, then east along the north of Greenland to north of Svalbard. 

The jet stream responds by its exit from the eastern seaboard being pulled a long way south between day 8 and day 16 beginning to split around the forming Atlantic high, here on the 12z GEPS.

 

Most of all I like this evolution as it’s the most reasonable roadmap that I’ve seen so far with good potential to lead to the destination mapped out by the CanSIPS and CFS monthly anomalies (run dates Dec 31st and Jan 15th respectively) for February…

 

…both with the European low anomaly, and strong heights to the west or northwest, and much scope to deliver a highly seasonal month. 

Despite the wait, plenty of opportunity for interesting developments to emerge along these lines (and potentially no doubt many others too!) in the next couple of weeks, as we move towards what could be a fascinating February. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019294

[Mike Poole]

ECM clusters T192-T240:

All show a ridge through the UK to Scandi, but this is much stronger on cluster 2 (20 members) than cluster 1, which has a more westerly influence. 

T264+:

The Scandi high option seems to no longer be on the table this morning, with a UK high being the destination in cluster 2, whereas the more mobile cluster 1 eventually puts up an Atlantic ridge.  This is the retrogressive option - and this seems to fit with the signal from the seasonals, and also the ECM 46 - which, as @blizzard81 noted earlier, was a stronger signal for heights to the NW yesterday than recent runs.  

I’m still not wildly optimistic that a cold spell is on the way in February, but all the evidence seems now to suggest that if it does materialise, it will be from height rises somewhere to the NW.  

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019542

[lorenzo]

58 minutes ago, Mike Poole said:

I read that blog, but one thing that confused me with that picture, is that the often quoted (on here, anyway) Ural high, Aleutian low combo, as a SSW precursor, isn’t one of the two main patterns. Instead the two patterns are Aleutian low, North Atlantic high (for wave 1) and Aleutian high, Ural high (for wave 2)?  In fact, the Aleutian low, Ural high is more similar to the left picture of what happened this year.  

Can anyone explain/reconcile this, please?  I am confused!

Had to rewind my mind back to 2009 - 2011 to get this one disentangled - there was a paper which referred to both the Ural High regime in combination with the Aleutian Low, and cited the NPAC low as a 'stratospheric starter pistol', a nice turn of phrase which sticks in the memory, which of the papers at the time examining precursors - have not been able to recall.

Looking at more recent analysis - found this paper which summarises both precursors and how they enhance wave activity / wave driving and create vortex perturbation.

 

• It has been shown that pressure changes in certain regions, when in phase, can constructively interfere with the climatological wave-1 and wave-2 patterns and thus lead to an overall increase of wave driving (e.g. Garfinkel et al., 2010; Smith and Kushner, 2012). In particular, the Ural blocking pattern as part of a wave-1 anomaly has been recognised as a precursor pattern for SSWs (e.g. Garfinkel et al., 2010; Cohen and Jones, 2011). Moreover, this blocking pattern has recently received additional attention, as it plays an important role in dynamically linking Arctic amplification and sea-ice loss to changes in mid-latitude circulation patterns via a robust but highly intermittent stratospheric pathway (Jaiser et al., 2016; Hoshi et al., 2019; Cohen et al., 2020; Siew et al., 2020; Jaiser et al., 2023): The strong reduction of Arctic sea ice in autumn and winter, in particular in the Barents and Kara seas, and the associated heating of the overlying atmosphere favour more frequent blockingtype ridges over northwestern Eurasia in early winter, which facilitate the enhanced propagation of wave energy into the stratosphere, where wave breaking can lead to a disruption of the stratospheric polar vortex (Overland et al., 2016; Crasemann et al., 2017).
• On the Pacific side, Ineson and Scaife (2009) demonstrate that a deeper Aleutian Low positively interferes with and strengthens the stationary wave-1 amplitude. Moreover, Bao et al. (2017) identify the positive phase of the Pacific–North American pattern (PNA) as a precursor of SSWs by means of constructive interference with the climatological planetary wave-1 pattern. Whereas the Ural blocking plays an important role in Arctic–mid-latitude linkages, the Aleutian Low and the PNA have been identified as a pathway connecting the tropical phenomenon of the El Niño– Southern Oscillation (ENSO) to the strength of the stratospheric polar vortex in winter (e.g. Ineson and Scaife, 2009; Domeisen et al., 2019).

In relation to the graphic it is clearly a different flavour of warming this year given it does not match the precursors shown, I do wonder if much of this is related to the Canadian Warming after effects from earlier in the season. We are either in a place where we have better tools to see CW type events more clearly - given the last few seasons has witnessed Nov / Dec wave activity akin to the CWs of early 80s, this season perhaps was a true CW event vs the prior seasons simply being early wave impacts on the developing vortex. It would be worthy of some re-analysis - am sure the boffins will be on the case and produce papers to examine the lead in to the short reversal over the next 12m.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019786

[Kirkcaldy Weather]

Lots to cover. 

 

"Now lets dive into the MJO because it carries importance at various levels.

This could have some impact with regard to an important evolution of the cyclonic developments across Canada into the Maritimes I'd still favour mid Jan but might be slightly later should we get the interference a la the CFS."

Hats off to the CFS yet again as it was pretty much the only model keen and picking up on the Indian Ocean Dipole causing some interference which I discussed in my post from Jan 2nd

As the MJO begins crossing through the Maritimes generally from Mid Jan as discussed this works to aid cyclogenisis with 2 main times of interest.

Storm Isha

Come Sunday evening [January 21st] we'll have damaging gusts particularly through the Irish Sea with effects being most impactful toward Wales up across Southwest Scotland and moving Northeastwards 

 

 

Heading toward Monday these highest gust speeds look to shift focus further southeast 

Further potential damaging gusts cannot be ignored as a possibility across Scotland on the back of Isha

Using the 200mb Velocity data we can watch these focal points as the MJO influence works in tandem to aid this initial cyclonic development with Isha 

To understand the next focal point lets go back to my comments from January 7th

 

"Again links with recent MJO phases this links with the PNA heading more into positive territory, door opens for a snowy system into Northeast America from roughly Jan 18th - 21st IMO '

This same system becomes our next area of potential disruption by January 23rd

You can also watch some of the next patterns setting up on the gif above linking to my comments from my post on January 11th

 

'Following the MJO passing across the Maritimes we begin seeing feedback of phases 1 and into 2 as January week 4 gets started a high forms toward the Maritimes which might extend through Canada, also I'm starting to notice the trend toward cut off low development toward Mexico, far Southwest US '

With the above we can see some of the important 500hpa setups developing into our current timeframe and into week 4 of January (and beyond)

Low pressures from Greenland and into the Arctic

High pressure forming across the Maritimes. A secondary high toward the Northwest of the US and Canada which links with PNA behaviour more on that shortly.

Formation of cut off low(s) in that southwestern America > Mexico regions which also will lead into PNA behaviour.

High pressures East of the UK.

'This will have a setup which favours a + North Atlantic Oscillation especially during January week 4, this favours above average temperatures. Initially there is also more of a -PNA which also connects with the above average temperatures across the eastern portion of America / Canada and Maritimes with below average further west.'

Following on from this as the preceeding MJO phases input begins to feed into the setups from week 4 of Jan onward the above remains true with further developments.

Looks like this initial cut off low will develop into a +PNA during the very end of Jan

 

As discussed above there continues to be the trend of the high extending across Canada

As we head into February and again as the preceeding MJO input begins to materialise this will see the high extension into the Atlantic with further developments of high pressure again toward the Maritimes.

This sees low pressure[s] becoming centred toward the north of the UK 

 

 

 

 

As discussed in my post from Tuesday we're seeing patterns favouring above average temperature scenarios across large swathes ie Europe and America particularly Northeast US and Maritimes > Eastern Canada. 

Colder temperatures become focused into Asia in association with these patterns.

 

I'm also looking toward the very last days of Jan and into February for stratospheric warming(s) as this is supported again with MJO feedback. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5019918

[Tamara]

1 hour ago, northwestsnow said:

I was really hopeful after reading Tamara's musings but alas there is precious little as it stands for us to hang our hats on

 

Fingers crossed we see improvements in the next few days, I personally thought EC det had some potential this morning ..

Just a response to this before vanishing into the background again. Musings based on the best information available at the time. Which matched the diagnostic evidence available at the time.

The SSW blip have been quite unusual with the incredibly powerful reflective nature of the wavebreaking.  Equatorward fluxing, strong Hadley cell, and very strong polar jet. As posted a while back - in these situations +AAM  momentum transport between the tropics and extra tropics to in turn perturb the polar field through +EAMT - will be negated by equatorward fluxing. Instead of poleward momentum higher latitude blocking, the downstream blocking resides instead across Europe. Sometimes these events hedge along fine lines which makes starkly different outcomes to the Annular Mode.

The science of the stratosphere has come a very long way in the past 15 yrs and the likes of @chionomaniacpioneered a lot of that for this site back at the time. However, and also in respect of the continued skewing of climate change effects - so much more is yet still to be unravelled.

On a personal note, following some very useful rain in the past week or so - the coming 10 days looks delightful down here. Blue skies, winter sunshine....and temperatures during afternoons into the low 20s across parts of the country. Portuguese weather bloggers are looking out for the 25C marker to be breached somewhere. Which even for this part of Europe would be quite something extraordinary in the last week of January.

Not what this thread is interested in, but best wishes to UK weather watchers despite their frustration.

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5020335

[Catacol]

46 minutes ago, Cleeve Hill said:

Hi Blue

Not really. Lots of tentative ideas for sure but certainly not as bullish as METO. I'm not being critical at all and when I look at the models we can see a pattern change in time but the signal I see is not as clear and straightforward for NW members to call it as the METO are. I hope they're right. 

Not sure who you have been reading, but the majority of the core posters in here that tried to read the season as a whole were looking at February to be the most significant wintry zone.

Im watching developments in the strat with a sinking sense of doom. Our tropospheric pathway to cold has been positive all season so far, and we have seen 2 out of 3 predicted cold snaps/spells come to pass, early December being better than expected and last week a bit disappointing. Xmas was a bust. But a fully reflective stratospheric response to the warming impacts that occurred through this month is exactly what we don’t want to see, and I have mused over the importance of the strat before as the dominant driver in most winter seasons. Early January we were so close to a major SSW - and it has now turned turtle and looks as though the strat will be above average before too long.

The science of strat warming impacts is still not clear. Even the big guns such as Butler and Cohen called a SSW for early January, reflective impacts not what was expected. It is way over my head as to why in some seasons the warmth is absorbed and breaks the vortex up, and other times the warmth bounces off the vortex core and reflects zonal forcing back into the trop. One thing I do know is that CC is cooling the stratosphere and, on average, this means stronger zonal forcing for each and every winter going forward. It is our CC winter handicap that every year we are going to need to see overcome.

Back to this winter. No doubt that tropospheric forcing is going to support blocking in the right places for U.K. winter starting approx next weekend. The strength of that forcing will build over the following 2 weeks. I had expected that to occur while we still had some blocking in place, but strat impacts have wiped that out in about 72 hours. So we have to build a blocking pattern from scratch. Quite doable….but not if the strat fires up and grabs control. Fine lines as ever, but I would say the odds of a cold February have now lengthened despite the confident assertions of the seasonal models and our reading of pacific led forcing.

Much to watch through the coming week. All eyes on the strat, perhaps for the first time this winter. We may have been guilty of downplaying it this winter, perhaps the result of a quiet @chionomaniac, and we have to hope that reflective impacts are being overplayed and trop drivers can seize control once again. For those of a research mindset this paper is interesting. 44 reflection events identified in the modern record, and on 35 of those events an SSW was prevented. These reflective events are common. See appendix A1.

Stratospheric downward wave reflection events modulate North American weather regimes and cold spells

WCD.COPERNICUS.ORG

---

Abstract. The Arctic stratospheric polar vortex is an important driver of mid-latitude winter cold spells. One proposed coupling mechanism between the stratospheric...

So much still to learn.

.

 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5020929

[Met4Cast]

What did previous look like a good chance of sustained high latitude blocking during February is rapidly fading. 

Despite an increasingly favourable MJO signal into the western Pacific, we’re missing a vital ingredient & that’ poleward propagating +AAM (westerly momentum). 

The arrow shows the previous “starting pistol” of +AAM anomalies propagating poleward through December & indeed into early January, this along with the MJO helped to support & sustain the recent blocking we’ve seen around the UK/over Greenland. 

Unfortunately, this time +AAM is increasingly glued to the equator & we’re not seeing this fluxing towards the pole, this helps (despite the MJO) to inflate the European ridge & indeed, a very strong signal for this within NWP through the remainder of January. A flat, mostly mild end to the month with low pressure systems deflected northwards, potentially stormy at times for Scotland. 

The reflective wave from the SSW hasn’t helped things either. So.. my hopes for something sustained in terms of cold/snow are rapidly fading. 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5022187

[Catacol]

1 hour ago, Penguin16 said:

But is it categorical that it was cut short by the SSW? or is it just a case of selective revisionism as to way to explain why the background signals were a major fail once again? Only 10 days ago we were hearing about a 1978 pattern from a god and to ignore the models breakdown. I’ve never seen one of the background zealots on here actually hold their hands up and say actually guys I got it wrong. There’s always an excuse.

"Background Zealots"? Hmm. Is this where we are at now, where those trying to unravel the complex task of forecasting get labelled as zealots? Either you know what that word means and are therefore genuinely trying to put the boot in, or you don't know what it means and perhaps shouldn't be using it.

I see in general the knives are out today. Disappointing. Let's have a go at a broad response:

1. There are 2 areas of ongoing research that interest those with a passion for this kind of stuff. First is the GSDM theory first put together about 15 years ago by Ed Berry. The second is a greater understanding of stratospheric impacts on our weather, another fledgling science that has also been around for 15-20 years approx.

2. One of the challenges of both approaches is to try and understand the inter relationship between the two. GSDM is largely anchored on developments in the Pacific alongside momentum impacts created by the big mountain ranges - Tibet and Rockies probably most importantly, Urals also. Strat modelling tries to interpret the impact of vertical wave propagation and how the column of air above the arctic is shaped/squeezed/stretched/split (or not) by these waves. Tropospheric patterns feed into the strat and vice versa - so they are definitely linked - but an understanding of the links is still in its infancy. When Amy Butler tweets that the reasons for the failed SSW in early January are not understood (given models tend to under rather than over model the likelihood of an SSW) then you know you are walking in a world of grey. And that failed SSW and what has transpired instead has had a huge hand to play in how January has developed.

3. From this, we have 2 options. Label these areas of research as a waste of time, as likely to produce accuracy as the advice of a cat (!!), or we engage with what is going on and try and unpick it. CC is not making this any easier because CC is making a mess of analogues - the atmosphere and the overall climate just isn't what it was in the 1960-90 period and adapting to the pace of change and how it impacts forecasting is a challenge.

4. Some of today's posters would clearly favour the former. Don't bother trying to unlock the door to understanding because it cannot be done. Fair enough - but not for me. I'm not a nihilist and wish to continue to try and learn. Perhaps those who see chaos theory as the only answer to our weather should have a thread all of their own, though the thread would probably make for pointless reading.

5. Finally - you might want to read posts more carefully. Only the other day I acknowledged in a post that the Xmas forecast was a bust, and that the recent cold was shorter lived than expected. Reasons for both were set out, bust was advertised. Two successes at the same time, early Dec and the snap just gone. And it looks as though next week will bust too. There you go - is that clear enough? If you want the reason laid out again, reflective strat event. Not forecast, not spotted even by those with proper qualifications in relevant climate science. But this winter is not done yet, and I still see distinct opportunity for further cold in February and again into March. 

 

As a concluding comment, we are dealing in probability forecasting. No one will ever get to the stage where we say "in 10 days' time it will snow in London and 6 inches will fall and stick." Nonsense. We look at probabilities. And when dealing in probability a 95% chance does not always land. I see some criticism of the MetO today as well. Really? Those of you happy to criticise forecasting methodology and happy also to criticise (possibly) the most advanced national Met Office in the world and its choice of language are seeking a level of absolute clarity that is unattainable.

If you have something to say that adds to the debate, say away. If your words are designed to tear, rip and demolish - silence is a better alternative.

 

Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5022417

[MattH]

Evening.

I scanned across a post earlier today, which discussed the AAM and how this is now unfavourable looking ahead, also referencing early Dec as being the onset of where the current blocking patterns and propagation of AAM anomalies to the mid-lats started - This is not correct.

I did a detailed post, using three separate examples which got pinned on how the last month or more, in terms of the AAM evolved and influenced the pattern. To use the current (20th Jan) GSDM data to write off the outlook into the first half of February, at least, is a mistake.

The MJO has progressed into phase 5 and there are now increasing -ve OLR anomalies throughout the Maritimes all linked to the expected eastward push of the MJO. Don't forget some of the key important phases, in terms of the MJO and the GSDM are phases 4-5-6. People often hope for phases 7-8 of the MJO.

The current evolution can be seen well on the below...The higher latitude -ve E'ly AAM anomalies have been replaced by a zonal push, won't repeat the reasons why that has happened, but, once again, the current and upcoming +AAM event and rise in GWO cannot be simply dismissed as an influence within the next 14 to 21 days because expectation is for the zonal higher latitude flow to persist, unabated. To say that we are missing a poleward propagation of +AAM anomalies is also incorrect, it is E'ly AAM anomalies that are looked for. This is the complicating area of the GSDM that needs to think about, as +ve AAM regimes through the tropics promote -ve AAM anomalies at higher latitudes and vice versa.

What I have been musing over is whether the more zonal, westerly type at higher latitudes will now remain dominant and acting to keep a lid on the potential for northern blocking, but IMO I don't think it will. We are now only just starting to see the usual GSDM responses to the ongoing MJO progression and the re-development of westerly inertia into the tropics, in the areas of interest. This remains a watching brief, but it is way (way!) to early to say that we won't see any influence through the mid-latitudes into early February onwards. Don't forget we maintain a robust eQBO regime too.

My expectation and prediction is that the current dominant zonal +NAO regime will, essentially, burn itself out within the opening week of February (approx), with a far greater risk of amplification to the pattern, this is perhaps particularly relevant if the sPV declines more towards Russia once again.

In terms of colder synoptics and February is very much a lot to play for, despite how some may be analysing the situation.

Regards, Matt.

 

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5022710

[Singularity]

Some here seem to view a strong Iberian high as a driver of weather patterns - but this is not so, it’s a response to drivers. In this case the forcing leads to attempts to establish a high over N Europe which are countered by the AO being too positive (likely related to the unusual stratospheric events - who’d have rationally bet on that one?), meaning that in a sense, amplification becomes trapped over S Europe.

Due to the MJO & AAM setup, further attempts to shift the high N are likely in the coming weeks (which can happen abruptly even with a strong Euro high). Signs are the first of those in 6 days time will likely fall short & boost the high over C/S Europe instead. Then, however, we are seeing the models tend to raise polar heights as we head into Feb. That improves the chances of the next attempt being successful, regardless of how current modelling paints the picture (they’re not actually that reliable for week 2+, it’s just easier to predict +NAO because it happens way more often than -NAO in N Atlantic climatology).

Emphasis on chance here. As Tamara has said many times over the years, there’s no magic bullet for HLB patterns. As I’ve said before, the most likely outcome isn’t always what happens. With this in mind I’ve found forecast model watching a lot less stressful.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5022887

[Stravaiger]

28 minutes ago, Penrith Snow said:

I a  not sure Singularity is correct about the Iberien High being a response not a cause, its chicken and egg.

Check out a 100 years of historical data pre 1988 and you won't find such a massive and persistent Iberain/Mediterranean High as we see modelled now, it just didn't happen and of course the current persistant Bartlett is only the latest in a long line since the 1999's.

IMO, the Iberian High dominance is due to the expansion of the sub tropical Hadley Cell in response to a warming world, the expanse forces the Jet Stream north preventing the PV leaving its natural home ie Greenland, it happens occasionally of course like last week but any change is pushing againt the new normal and is quickly crushed.

This I feel is the over riding factor and overwhelmes other natural signals that might encourage Northern Blocking, hence the late January early February forecast debacle.

Watch the MJO if you like but it will make little difference 

Andy

This - 100%. So often climate change isn't looked at as a driver but it has fundamentally changed the game. Expansion of the Hadley cell, GHG and CFC-induced stratospheric cooling leading, etc., all of these factors are uniting to increase the likelihood of strong, coherent PVs and a northward push of the sub-tropical high into Southern Europe during winter.

Of course there will be times when other drivers can override these factors and we get pressure in Europe to fall - we've seen it a few times since November - but the winter season is fundamentally changed by the increased likelihood of long periods where really high heights to our south effectively block any cool or cold air from covering the British Isles.

The way I think about it is that we're playing the same game but the cards in the deck are different now, with many more leading to anomalously mild conditions. We'll still occasionally get to play great hands but the odds of them appearing have lengthened considerably.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5022916