Model output discussion 24/01/21

[Vikos]

16 minutes ago, Daniel* said:

No they aren’t smaller details as Nick S mentions domino effects from smaller changes. There’s nothing wrong with Canada going very cold it’s very normal for them when part of polar vortex visits them, we don’t see same as there’s big modification from sea. There’s satisfactory cold to NE as long as E Conus doesn’t go into freezer it’s not a concern. You’re worrying over nothing. 

Am I? My random (collected) worries...

Edited January 26, 2021 by Vikos

[damianslaw]

Another interesting set of model runs - small fine margins in the short term between cold and unsettled or mild and unsettled - the lines pivoting through N England and S Scotland. Tomorrow looking a rather drab lacklustre day with not much happening and milder for many away from Scotland. Thursday provides more snow potential for northern half of UK especially places with height. Friday we see colder air moving back south as a weak build of heights develops to our north.

Another cold weekend ahead in store, Saturday hopefully should be mostly fine with early and late frost. Sunday and the models are showing a negatively aligned front off the atlantic bumping into the cold surface air, a recipe for snow - the front looks quite slow moving.

Sunday is the edge of reliable. Into next week and continued signs of the cold vs mild theme, heights to our north, low pressure further south through the UK, opportunity for further trough disruption, slider frontal features, all dependent on how strong an influence the heights to the north exert themselves.

A much colder pool of air is set to develop to our NE and if we can tap into this then a more notable colder spell could appear during first half of February, and by February I always think the continental air masses are more likely to oust aside the atlantic.

[Tim Bland]

33 minutes ago, Man Without Beard said:

 

The more progressive runs on the ensembles may see a very quick snow to rain event, but the runs that follow the mean could require a digger to dispense with all the snow. 

My suspicion is that latter will outnumber the former ... I'll check later

EDIT: Checked all 51 runs for snow by Monday morning - Yes, most runs have a strip of snow running in a line running in a SE to NW direction, somewhere through the UK (and particularly England/Wales) - but where exactly that line will be, you'll need to fight over for now. Could be anywhere. 

Good stuff!! Do most of these members take the snow band from west to east so affecting most areas at some point ...or do they fizzle out in situ or sink away south ? Will it snow in Carlisle ?

[Weather of Mass Disruption]

1 hour ago, BLIZZARDMAN said:

Don’t take anything in FI as facts, I was supposed to have a sleety mess according to most models on sunday this time last week but I did just fine! Upgrades nearly always appear nearer the time.

As do downgrades for those residing in the South West! 

[Man With Beard]

14 minutes ago, Tim Bland said:

Good stuff!! Do most of these members take the snow band from west to east so affecting most areas at some point ...or do they fizzle out in situ or sink away south ? Will it snow in Carlisle ?

A mixture of options here. Many runs sweep the snow across the country but also many runs limit the snow to a regionalized area and it makes no more progress further north. Perhaps slightly in favour of the "moving north" option. Not many runs have no snow event at all.

However it definitely will snow in Carlisle if you slip me £50

[Mike Poole]

Hi folks!

Busy early evening today so just catching up.  Really positive output on the 12s today, yes the models haven’t nailed a proper cold spell yet but are edging towards it, which as good as we can expect given recent output.  

ECM clusters are out, T192-T240, all charts are green border (-NAO) and so all show some kind of high latitude blocking, and undercutting lows:

Moving on the T264-T360 charts show some charts with red border (Scandi blocking) and you can see this in the 2nd cluster in particular.  

It would be a brave person to predict a mild outlook for the UK based on that...we will see.

[ALL ABOARD]

Icon goes for a snow event south Wales southern England again. 

Then this at 105.. 

Were not far away from a great undercut. 

 

[ALL ABOARD]

Second Slider alert.... 

 

 

 

[sheikhy]

Icon 18z hold backs the low at 120 hours and disrupting!!more like ecm mean!

[Allseasons-Si]

The latest from the cpc starting to show northern blocking now in the ext with trough S of the UK as does the day ten EPS,also ridging starting to show in the Atlantic,these are very similar to the one a few weeks ago when we had that trough drop down from the NW

as has been mentioned quite a lot over the last few days is the MJO and these are quite amplified into phase 6 and traversing into phase 7 in the ext

ext ECM,GFS and CFS,the ECM starts to head into the COD(circle of death) by the 24th Feb but that's a long way out

The latest EPS and ext EPS are a notch up on last evenings with regards to a ridge showing in the Atlantic and up into Greenland by day ten on all clusters,i will snatch someone's arm off for cluster two in the ext with that big fat Scandi high.

all these are speculative at that range of course when we have plenty to work out this week never mind ten days plus but we look for consistent trends that far out and @momentum is swinging to a colder side as we go into week two so stay tooned

Edit: just seen @Mike Poole's post above, great minds alike

 

 

 

 

Edited January 26, 2021 by Allseasons-si

[WINTRY WALES]

Firming up it seems on a potential widespread fall late weekend into next week...hopefully cold digs in so it lasts a while too! 

[chionomaniac]

6 hours ago, Tamara said:

Posted by chionomaniac last Saturday:

Just reading through your post, and the one thing that I notice is that despite the drop in GLAAM, and a reduction of the more Nino-ish December response, we have yet to see a traditional Nina H500 pattern to develop. I suspect that we have to grateful for the SSW for that - not only for well recognised polar and mid latitude responses, but also the feedback indirectly to tropical regions. I know that there are those who are far more qualified to put more meat on the bones regarding this than me and there have been a number of papers on this in the last few years, but it is another wild card thrown into the equation.

And, if you had to, and your life depended on it, what would your punt for February be? After all, you have spent years on research of mid latitude responses to tropical forcing, it would be great to see the end product of what you consider more likely. One of the reasons, that I suspect you don’t or can’t ( you are not alone) is the lack of forecast data in this field. This would help a lot. When looking at the data, it is recording what has already occurred and the MJO forecasts are reliably unreliable. This makes commentary on what has happened far easier than being able to predict in the mid range. 

I think that the sooner that we can get more pieces in this jigsaw, the better.

-------------------------------------------------------------------------------------------------------------------------

 

The H500 pattern has been very consistent with a Nina response. The crucial aspect, as you allude to, is that it is a Nina response in tandem with a disrupted stratospheric profile. 

At least a couple of previous posts have commented on the upstream pattern switch to Aleutian heights in response to the GWO moving into the Nina attractor phases heading into the second third of winter. The GWO, phase depiction of global wind-flow within the tropics and extra tropics, being a precise barometer of tropical>extra tropical pattern response on hemispheric levels.

Amplification within the Pacific, very characteristic of La Nina signature, pushes inertia into the downstream polar jet, which is exactly what we have seen. However, the disjointed zonal wind anomaly within the polar field, leading to very weak and erratic flow, has meant that the usual (traditional) downstream response of jet stream flow has been rather blockaded with the result of southward and equally fractured flow rather than the flatter zonal flow across the North Atlantic seen under a more traditional response. Hence the shallow tropospheric 'cold' ridges that have disrupted low pressure systems in the way that has been seen. Nonetheless, there has still been just enough inertia to keep the pattern relatively flat and 'faster' than under a more meridional downstream Nino-esque regime

As the response to a post below also suggests, this diffuse stratospheric>tropospheric response is not new, and was seen to an extent following the SSW of late January 2009 - during February 2009. There were very strident immediate expectations following that particular SSW, but the combination of La Nina and w/QBO at that particular time of the solar cycle provided a much more diffuse tropospheric response than the  subsequent bookend part of the year which saw a classic Nina-esque stratospheric pathway during Dec/Jan/Fed 2009/10. Indeed, the response to the SSW of Jan 2010 was a more 'classic' cold pattern response than that of a year previously. The first part of the season was troposphere>lower stratosphere led (and actually the deepest cold weather of the season) before the upper part of the stratosphere warmed considerably and maintained the unstable (cold pattern) tropospheric pattern of the first part of the winter.

I think for the weather pattern observer those two seasons, a decade back, is a reasonable case study that gives some clues as to the manifestation of this winter (but with further added climate forcing another 10 yrs on - though that is not for this thread) That is the closest I would get to any 'punt' And for good reason, quite apart from not having the same weather preference motivation for specific weather type as most other.

With  all that in mind, and notwithstanding the credible correlations of the comparisons  - one thing that has been learned over years passed -  is there is no one size fits all response and each situation/pattern/set of variables have to be taken on their own merits. That also leaves making 'punts' a little redundant from my point of view. Whilst not a forecaster (and just one of many reasons not to be) is that analogue pattern matching, however unintentionally, tends to be skewed by bias confirmation as well as the added superimposed forcing on the climate which has distorted feedbacks, year on year, across the tropics>extra tropics and at the pole.  However, the GSDM still remains a highly worthwhile aid to diagnosing the vicissitudes of numerical modelling and the inherent biases of these models. What you get with a global wind-flow budget remains a precise measure of inertia within the hemispheres at any given time, which inclusively calculates the superimposed forcing that is almost insidiously being added year on year.

One good reason why so many tropical (MJO) and extra tropical (GWO) phase composites need to be readily updated as a perpetual 'work in progress' to take account of pattern responses according to the ever more volatile wind-flow profiles according to progressive broadscale warming trends.

 

Its that stuck record once more but any comments related to trends have to take into account all probabilistic outcomes and not just the one that human intervention would like to steer towards.  As stated above, recent summaries have commented on the diffuse weaker than average westerly gradient of this season and, stripping away all the repeated detail and analysis, the likely outcomes as being a N/S or NE/SW divide. That suggestion has continued to play out and remains well advertised in the further outlook. - if one takes out the usual speculative outputs that tend to catch the eye on this thread and are given maximum exposure  The disjointed and rather unstable polar profile should continue to steer low pressure systems on a more southerly track and invite some cold air advection in their wake, with more northern latitudes seeing these the most. However, the continued expectation for the MJO to be a magic bullet to a definitive  sustained cold block requires greater objectivity as (keeps being repeated) it is not as straightforward as x ingredient = one specific y outcome.

There is no doubt that the La Nina-esque atmospheric profile that has taken over since the end of the first third of this season is assisting the diffused tropospheric response seen similarly on occasions such as February 2009, when the combination of robust tropical forcing lead to equally strong extra tropical +mountain torques inducing a highly significant SSW (when viewed under w/QBO and La Nina profile). There are some similarities, at least, to that time - and the context of the upcoming pattern phase should be viewed with a similar perspective - and that includes the sort of initial blocking responses as seen early in Feb 2009 which, (at least for those disposed to deep freezes) appeared to offer much but actually in terms of longevity fell a long way short. This suggests there certainly IS wintry potential for the UK looking ahead into February, but this is set against a profile that is rather working against the sort of prolonged and sustained very cold spell that might be achieved otherwise.   Equally however there remains other outcomes which will likely not get coverage on this thread.

That is about as off the fence I would, realistically, and equally reluctantly want to move. So, yes, not very much off the fence at all then.....From a (boringly) neutral  and very detached perspective I am far, far more interested in the overview than a specific weather outcome.

 

I had to read your post a couple of times, Tamara and thank you for replying. I do think that the real advance of coming to terms with how tropical responses can affect longer term mid latitude outcomes depends upon being able to make structured forecasts (not punts) on the tropical base states. Otherwise we can become experts at retrospectively analysing tropical events but useless at forecasting based on these events. Surely, the reason in understanding GLAAM, and responses to these events is to give us a stronger capability to forecast further ahead than we would ordinarily be able to, based on them. If we can’t then is there any point? I suspect that it make take some time and a number of years before this is possible, but it would be great for someone who has such great knowledge to be able to move us towards that next stage forward.

And as you know, as you were analysing the Jan 2009 SSW response we were fortunate to get the immediate response from the split vortex but longer term underlying tropical imprints may have overridden the strat in prolonging the response. So much to learn, and I look forward to the day when you feel more confident to predict the mid latitude response to tropical events to a specific outcome.

[Allseasons-Si]

22 minutes ago, Bartlett High said:

Marginality is my most disliked word this winter.

Marginality brings with it the best snowfall BH 

IE:-

warm moist air clashing with cold dry air=battleground,... but that depends where you are in this country as usual 

Edited January 26, 2021 by Allseasons-si

[SqueakheartLW]

A few colder scenarios from the 12z GFS ensembles

Scenario 1 - Member 29     Will it push NE or will it do slidergate?

+144 hours

A classic here with a real risk of a snow event on the NE side of the nearest area of low pressure but what happens next. The first low pressure does indeed slide SE after delivering a snow event to central England and N Wales in particular, more likely rain to the S of this and the colder air remains in place to the north.

+168 hours

What eventually spoils this cold pattern isn't the low to the west but a new one that forms over Biscay and this pushes much milder uppers into the UK, blowing away the cold

+216 hours

+312 hours

Scenario 2 - Member 27     Will it stick or will it topple version 1?

+210 hours

This looks promising for a colder spell with N to NE winds blowing with a snow shower risk for the N and E in particular but does the pattern set in or get blown away. The simple answer is that the Atlantic combo of Greenland low and mid Atlantic high simply blows the colder pattern away and we end up back to default westerly too quickly

+288 hours

Scenario 3 - Member 23     Will it stick or will it topple version 2?

+348 hours

A more definite colder N to NE wind pattern here that looks to be in a better position than the previous one but does this one stick for longer or does it also do the dreaded topple too

+384 hours

The simple answer is that the pattern holds a bit longer and the cold is still there by the end of the run but there are signs of a possible topple taking place or a possible temporary less cold push off the Atlantic before another low dives down and creates a reload of the cold pattern again

GEM Fantasy beasterly charts

Just to finish on and to get all coldies in the mood for beasterlies here are two decent ones showing up in the 12z GEM and its ensembles

Member 14

Member 18

[Had Worse]

Just now, Allseasons-si said:

Marginality brings with it the best snowfall BH 

IE:-

warm moist air clashing with cold dry air=battleground,... but that depends where you are in this country as

Excellent analysis and answer.

[Allseasons-Si]

12 minutes ago, sheikhy said:

Icon 18z hold backs the low at 120 hours and disrupting!!more like ecm mean!

Blimey!!!,.. is it that time already!

That is some shift SE mate

18z 120 v's 12z 126.

 

[Lord Grogon]

14 minutes ago, Bartlett High said:

Marginality is my most disliked word this winter.

It’s part of a special group of painfully frustrating terms including:

Uncertainty

Battleground

Midlands North

Downgrade

Pesky shortwave

Dew points too high

Usually correct south

Still waiting for the effects of the SSW.

Phasing issue

 

[Cheshire Freeze]

4 minutes ago, Allseasons-si said:

Blimey!!!,.. is it that time already!

That is some shift SE mate

18z 120 v's 12z 126.

 

Going on trends, I reckon that Sunday low may produce a snowfall for Wales and the Midlands with the N extent perhaps being Manchester?

[Allseasons-Si]

3 minutes ago, CreweCold said:

Going on trends, I reckon that Sunday low may produce a snowfall for Wales and the Midlands with the N extent perhaps being Manchester?

I wouldn't care if it was to go further south and we miss the snow again if we all benefit a quicker route to cold from the NE,win win!

[Allseasons-Si]

This is the most NE'ly extent of  Saturday's front before it pushes south on the ICON

then Sunday has this

 

[AFCBSNOW]

18 minutes ago, Lord Grogon said:

It’s part of a special group of painfully frustrating terms including:

Uncertainty

Battleground

Midlands North

Downgrade

Pesky shortwave

Dew points too high

Usually correct south

Still waiting for the effects of the SSW.

Phasing issue

 

AND.................................. Marginal and Raging Zonality!!

[Day 10]

18 minutes ago, Lord Grogon said:

It’s part of a special group of painfully frustrating terms including:

Uncertainty

Battleground

Midlands North

Downgrade

Pesky shortwave

Dew points too high

Usually correct south

Still waiting for the effects of the SSW.

Phasing issue

 

Day 10?  

[Methuselah]

1 minute ago, AFCBSNOW said:

AND.................................. Marginal and Raging Zonality!!

And [model of choice] is always too progressive, and underestimates the resilience of Scandinavian HPs...?

[Griff]

Just now, General Cluster said:

And [model of choice] is always too progressive, and underestimates the resilience of Scandinavian HPs...?

Not too progressive.... Here... 

[Allseasons-Si]

21 minutes ago, Lord Grogon said:

It’s part of a special group of painfully frustrating terms including:

Uncertainty

Battleground

Midlands North

Downgrade

Pesky shortwave

Dew points too high

Usually correct south

Still waiting for the effects of the SSW.

Phasing issue

 

You have missed a biggy there LG

"potential"