Model discussion highlights

[Eagle Eye]

Right now, we had the large EHF prevalent over the Ural-BK region backing up the first warming wave which is going to drive it towards the Pacific-North American are though that thermally dampens the Ural-BK area as the -VE EHF's are forced into the Scandi-Ural area. The anomalously strong planetary wave-breaking for thermal strengthening of the Wave-1 strength over time and increasing the Baroclinic tilt of the vortex through the Tropopause drivers for Strat 'kicking' of the riding outer wave. Therefore, the progression of Wave-1 would suggest movement of the +VE anomalous thermal line to be more West allowing for the strong thermal energy Tropopause transport across the Atlantic signalling for extratropical thermal increasing of Wave-2 formation for the mid-Atlantic progression towards the Scandi-Ural-BK area. Scandi-Ural driving was the rough area for thermal flux initiation of the 2018 SSW when combined with the Alaskan block (I think?) so that would generally be a good idea to get that movement but at this range, the Wave-2 may weaken and/or not transition towards the Scandi-Ural-BK region. The driving of the Alaskan +VE EHF's at the Tropopause are the main reason for the strongly stretched Polar Vortex as the wave pushes into the North American area of the Vortex. This type of wave breaking through the Alaskan area suggests a quasi-horizontal thermal transport stretching the Polar Vortex and reducing the circulation of the polar-night jet via the latent heat release and radiative transfer into the initial area of quasi-circulation (though not a split) and that spreads the centre of the 'spinning top' and stretches out the Polar Vortex though that mainly relies on the timing between the Alaskan and Atlantic warming to increase the 'double trouble' on the PV. The equator-pole Eddy driven circulation with the 'surfing' Waves is typically characterised well in general despite the troubled understanding of The Brewer-Dobson circulation ("The Brewer–Dobson circulation (BDC) describes the net transport of mass, heat and tracers in the stratosphere and therefore plays a primary role in its chemical composition and radiative transfer properties") because of the typically Wave-1/Wave-2 setup for the Strat; though I suspect it underplays the role of Wave-2 setups (e.g. displaying a strong bias on most models) as that requires a fairly well modelled understanding of how thermal and mass transport occurs under Eddy-driven circulation. 

Essentially what I'm saying here is that the combination of the driving via the Ural Block (and heat flux) and the Alaskan heat flux should result in the driving of the Eurasian warming towards the Pacific and connect up with a developing +VE Alaskan wave to stretch the Vortex a bit. At this point everything becomes complicated and affected by every other thing as without a developing Atlantic-Europe Wave, the Vortex doesn't lose it's polar-night jet signal much, instead it's displaced to over us (e.g. not what we want) but if we can get a warming Wave over the pre-mentioned area; then that should stretch the Polar Vortex and at least slow down the mean to average to below average I would suspect. Beyond that, we need the signal around the Scandi-Urals area to repeat and that would likely cause at least an attempt at a split. Obviously, we need a lot of things to go right for us but that's what luck is for right? Seeing as we haven't had much recently, a good dose of it this Winter (the first spell though came without much snow, then perhaps the second Polar Maritime spell) and maybe we could get a SSW. It's a long process yet the actual end goal would occur in such a short amount of time but it's the setting the Stratosphere up for a SSW that's really the main problem.

When looking at the Tropopause signal you of course have to look at Wave-1 and Wave-2 amplitude for the general signal beyond the output for the main area of the upper Strat signal. Wave-2 in the Tropopause (ish) area is on the up towards the end of the run and whilst it doesn't look significantly strong it's a start and may begin to back up the movement of the Wave-2 area towards the Scandi-Ural area as the amplitude increases and likely with it, the poleward movement.

 I was going to write a little more but I feel like that's enough for now...

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4786995

[bluearmy]

i think we have the biggest opportunity since early December for some scandi ridging in two weeks time 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787326

[Nick F]

10 minutes ago, northwestsnow said:

And award for the lead balloon post of the evening goes to.....

Of course this was only going to be 2 to 3 day  cold window.

Let's hope the strat events help us out  into Feb..

Certainly signs of a weakening of ZMZ winds at 10 hPa from GFS towards late month, a few ens members reaching 0 m/s, but a long way off yet to have any confidence in a SSW later this winter.

Closer in time, despite T850s nowt to right home about next Tuesday and DPs marginal, heights are rather low (low freezing level) - so snow more likely to fall at lower elevations - especially if heavy precipitation. But cold enough surface temps to settle another issue, especially if windy with that deep low on EC, as may be too much mixing and less evaporative cooling than with lighter winds to lower the temp to 0C. Likely will be very marginal away from high ground.

 

Still, expect changes, GFS doesn't have that deepening low drop SE like EC or UKMO. A very active and developmental pattern early next week, with potential for lows diving SE to explosively deepen if they move on to the cold side of the strong jet diving SE and phase favourably with the jet streaks and shortwaves. UK on cold side of the jet, so these lows will bring snow for some.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787345

[Nick F]

The trough that digs south across Europe early next week looks to get quickly cut-off into a closed low over the central Med by Thursday next week on 06z GFS. Unfortunately because the TPV remains strong over the arctic the jet returns zonal pretty quick and forces the Azores high into SW Europe, this had support from 00z GFS and EC ensemble means too for the end of next week.

So we could be looking at 2-3 days of cold enough to snow to lower elevations before it turns less cold from the west later next week, but Pm cold incursions rarely last long normally. 

Not entirely convinced the models have a handle on Atlantic amplification from the middle of next week, so we may see further changes beyond the cold surge from the NW on Tuesday - which has increasing confidence of happening. Hopefully the cold polar flow next week can deliver, because it may not last all week.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4786919

[Mike Poole]

34 minutes ago, ANYWEATHER said:

Away from the North and high ground to the south, it will be largely cold rain, maybe some fleeting attempts for snow to fall at lower levels ,but a Slush fest rather than a snow fest for the majority of lowland populated areas...

This view cannot be justified on current output, there is much more uncertainty and will be for days to come.  The detail of how the lows and disturbances behave in the cold flow will be vital in determining snowfall, the charts @Tim Bland posted, copied below offer potential for many areas a week from now, with modestly cold uppers, I would suggest.

23 minutes ago, Tim Bland said:

UKMO  

Anyhow, on to the ECM!

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787207

[Nick F]

Better upper trough shape digging into Europe later next week on 18z compared to 12z and particularly 06z means cold upper air keeps pouring south into Europe from the arctic - so the trough doesn't close off and form a closed low over the central Med like previous runs. This allows a northerly flow to develop and maintain, rather than a westerly. 

Compare 06z and 18z GFS  for 00z Friday 20th 

06z                                                      

18z

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787411

[Duane S.]

Charts of the day for me are for what’s going on way above our heads in the stratosphere. As has already been highlighted, we have a strong warming now down to the 10mb level

Further up right at the top we can see constant warming right through from now to D16, waxing to very warm and only waning a bit each time before another pulse hits. This is going to cause serious damage and it will as always be a case of how far/fast it propagates downwards.

We can see how the SPV at that level is fairly unperturbed by the warming here at D0

 

 

Here at just before D5, the warming strengthens and first signs of the top of the vortex getting some pressure on it

 

Go forward just a bit to just past D6 and the warming is really strong now, you can see the vortex getting pushed and starting to become enveloped, which invokes a squeeze.

 

More pressure being applied, in fact it’s pretty relentless. This at just past D8…

 

 

On to past D12 and the vortex is a shadow of its former self at this level. Weakened and susceptible.

 

And finally after all this pressure we get a split.

 Bear in mind that this is playing our right at the top of the stratosphere and we will need it to work down to affect our weather and even then, it only increases our chances of a cold spell (assuming it does work down), never guarantees it. And obviously these are just forecasts, but I suspect even a watered down version is going to cause the SPV a lot of unwanted pressure and translate into a very interesting period of chart output over the coming weeks. But it is encouraging to see very decent warming forecast to get down to the the 10mb level and below over time

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787523

[carinthian]

Morning all , irrespective of what ECM is showing post 168t and who knows what those charts will lead to ? The team over here are really excited for snow prospects  during period (132-168t  ) with the snow computer in its fine mesh outputs showing some quite substantial snowfall amounts locally. Further a field, quite a bit of snow cover during this period across much of the UK  with some very cold air in the mix. Still another 24 hours needed for the models to a firm up what is likely to develop in the sinking polar trough across the British Isles. Could be some exciting charts for you guys.

C

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787566

[nick sussex]

I’ve done a couple of paint jobs on the ECM day 8 ,9 and 10.

The first shows some energy disruption circled red over the UK .

You can see upstream the flow beginning to re-amplify circled red .

Then onto day 9 the troughing upstream is digging south , the effect of this is to try to throw a ridge ne ahead of that , if you look downstream that previous energy which is disrupting has cut se into the Low Countries and that small Scandi high is forming .

I think if this trend continues there will likely be two attempts to advect the cold west . Either that shortwave energy on the first attempt or if you look upstream that troughing below could eject shortwave energy into France then into northern Italy developing low pressure to support the Scandi high and help pull the colder air westwards .

Essentially the more dig of energy south into the Atlantic  off that elongated troughing the more northerly latitude the ridge thrown ahead of it will reach.

You need sufficient amplitude upstream to aid with the down stream jet cut back towards the Low Countries .

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787598

[carinthian]

2 hours ago, carinthian said:

Morning all , irrespective of what ECM is showing post 168t and who knows what those charts will lead to ? The team over here are really excited for snow prospects  during period (132-168t  ) with the snow computer in its fine mesh outputs showing some quite substantial snowfall amounts locally. Further a field, quite a bit of snow cover during this period across much of the UK  with some very cold air in the mix. Still another 24 hours needed for the models to a firm up what is likely to develop in the sinking polar trough across the British Isles. Could be some exciting charts for you guys.

C

Just an update. The next 24 hours will be crucial to see increased prospects in snow potential. Currently the upgrades continue. Lower 850mb temps obviously help but forecasters nearer to any snow event will be looking at wet bulb freezing temps in their predictions, especially under area of low pressure with plenty of moisture. A surface temp of 1.5c with RH of 85% would calculate a negative wet bulb temp and hence snow will fall. Predictive charts for say 120-168t period at this stage very much rely on upper air values but nearer a snow event , now forecasting comes to the fore. So what I am saying,all the snow prediction charts , especially in marginal situations frequent to the British Isles are still not to be taken at face value. However, looking good for some wintry weather next week across Blighty.

C

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787678

[nick sussex]

The Euros have a different view of the PV over Greenland and this will lead to a flattening of the pattern.

The ECM has the coldest 850s earlier on and those shallow shortwaves running se are more likely to deliver snow because of that .

The GFS has the best potential in terms of extending the cold but on the reverse side isn’t as cold as the ECM upto day 7 .

By day 8 the ECM tries to disrupt some energy se , this is a departure from its previous run .

Day 9 is somewhat interesting ! it begins to re-amplify the upstream pattern and with a lot of energy digging south this tries to force a ridge ne ahead of that .The earlier energy disruption cutting se helping to promote that high over Scandi .

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787502

[Nick F]

06z GFS now got that low that EC had yesterday tracking southeast across the far SW and on into France and deepening as it does so.

Highly developmental and fluid next week, given there's a strong jet streak moving southeast just to the west and southwest on the western flank of the polar trough sinking south, so expect more changes to where lows track and deepen, depending on if they engage the left exit of the jet streak and also whether they move on to the cold side of the jet (where they will tend to deepen more) or stay on the warm side and stay shallow.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787631

[Catacol]

Morning all - so where are we? I'm in bullet point mode at work - let's do the same here:

1.  Bang on time - better charts for the second half of January are emerging.
2. Lagged impacts of MJO phase 6/7 likely to be having a positive impact.
3. Lagged impacts of +EAMT which have set the Pacific Jet on fire are working their way through to the Atlantic. This means amplification.
4. Ongoing Aleutian Low is guaranteeing strong wave 1 pressure on the SPV. Slightly less convincing shape of forcing on our side of the globe around Urals - but while the forecast comes and goes we certainly have some hope/confidence in sufficient Ural forcing that talk of an SSW will not go away yet.

Product = 

a. Amplified Atlantic and the models are now sold on a mid atlantic ridge. Somewhat against what old hands have witnessed with these in the past, it is looking as though this one is going to produce a cold dig on the eastern side that will last longer than many and be colder than many. 
b. Lagged impacts of MJO forcing will be adding weight to a more -NAO profile in general. This looks to being overridden by the overall strength of the atlantic, but what is happening in the meantime is a developing signal for the Azores High to ridge helped by MJO backing and overall amplification. The ECM op this morning was an eye opener in this regard today and maybe - just maybe - those of us who have kept saying "Scandy High" all damned season long so far won't be left peeling egg off our chins forever.
c. Overall - we have a snow event on the horizon. I don't think it classifies as "epic" - but given we are seeing more extreme events everywhere these days perhaps it is wise to rule nothing out. Some NWP runs recently are forecasting a pretty deep trough to pay us a 3 day visit in a northerly airstream and that has to be better than the atlantic mush we have had for the last 2-3 weeks since the collapse of northern blocking just after Xmas.

Where next?

1. Enjoy next week. 
2. The fast firing Pacific Jet will swiftly retract. This is being shown in the forecasts. If any cold is to be long lasting we need to see a block emerge and gain traction BEFORE the lagged impacts of the weakening jet work their way through. If we don't get it - and on the balance of probability and historical precedent the odds are likely against it - then the atlantic will gain a hold once again for another phase. But maybe the ECM today can get us a decent Scandy High. Has to happen eventually.......
3. Much longer term - SSW or no SSW? That is the question. BA earlier was right - an SSW in late Jan probably means greatest impacts in March. Seen that before - bit disappointing for those looking for proper cold when it really counts - but such is the way of things. Still a watching brief here to see whether it happens at all.
4. Gloomy final point - if cold next week becomes a snap rather than a spell and we dont get a high lat block in place then the pattern will flatten exactly when MJO forcing supports a +NAO shape for the start of February. So - westerly first half of February before MJO enters more favourable phases in time for the end of the month. Maybe a combined MJO 6/7/8 on top of a split SPV for the very end of winter? That would be the final bite at the cold weather cherry.

For now - watching NWP developments with interest. Good that some of the forecasting of the last week or so has shown some degree of accuracy for this next phase. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787709

[Mike Poole]

ECM clusters again with plenty of interest, T120-T168:

Really can’t see much difference here for the UK trough, maybe a look at the individual runs later will help, minor differences in the areas of higher heights further away.

T192-T240:

UK high evolution in cluster 2, cluster 1 looks like the GEM op to me with heights into Scandi - looks good actually, and cluster 3 (including the op) headed for scandi, but also higher heights to the NW.

T264+:

Clearly lots of uncertainty here.  Clusters 1 and 5 closing in on an easterly around a Scandi high - both together 18/51 members.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787554

[Kirkcaldy Weather]

On 09/01/2023 at 13:56, Kirkcaldy Weather said:

Today + Tomorrow seeing the most extreme of the Atmospheric river conditions so far

Day 1 Valid 12Z Mon Jan 09 2023 - 12Z Tue Jan 10 2023 ...A MODERATE RISK OF EXCESSIVE RAINFALL CONTINUES ACROSS A LARGE PORTION OF CALIFORNIA, INCLUDING THE BAY AREA AND MUCH OF THE CENTRAL VALLEY... ...NUMEROUS FLASH FLOODING EVENTS LIKELY, SOME POSSIBLY SIGNIFICANT, ESPECIALLY OVER BURN SCARS... A more significant, elongated Atmospheric River (or AR) event is already beginning to impact much of CA ahead of a more amplified upper trough, effectively tapping into the subtropical regions of the north Pacific. Guidance continues to show PWs climbing between 1.25-1.5" (highest along the coast, and easily surpassing the max moving average per OAK and VBG sounding climatology), with southwesterly 850 mb flow peaking between 60-70 kts. Low to mid-layer moisture transport will be quite robust, as the 850-700 mb moisture flux peaks at 5 standard deviation range above normal, per the GEFS. Meanwhile, some elevated instability (at least 200-400 J/kg per the ECMWF, GFS, and HREF mean), along with the degree of deep-layer forcing and moisture, would support peak hourly rainfall rates of 0.75-1.00+ inch (especially within the Moderate Risk area). Overall, guidance consensus remains quite good with respect to the QPF, with 24 hour totals between 2-4+ inches over most areas (along with pockets of 5-8+ inches along the coast-coastal ranges and across the western slopes of the Sierra Nevada). This will be a fairly significant event as far as ARs go, with the latest deterministic QPF indicating a 5 to 10 year average recurrence interval (or ARI) within portions of the Moderate Risk area. In addition, the latest HREF 40km neighborhood probabilities of 3 hourly QPF exceeding current 3 hour FFGs climb to >50% within the Moderate Risk area after 15Z Monday. Considering how wet the soils will be ahead of this event (over the 90th percentile within the top 100 cm across the majority of the outlook areas per the latest NASA SPoRT), impacts from flash flooding or more rapid inundation will become increasingly likely -- especially across the several burn scars since 2020. Churchill/Hurley Day 2 Valid 12Z Tue Jan 10 2023 - 12Z Wed Jan 11 2023 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF SOUTHERN CALIFORNIA... Maintained a Moderate Risk area for excessive rainfall across portions of Southern California. Models continue to indicate a distinct southward shift in the QPF maxima on Day 2, with significant rainfall already expected to be ongoing Tuesday morning across upslope portions of the Transverse Ranges (with as much as 3-6" having already fallen on Monday and Monday night). Long duration of southwesterly flow will allow for another 2-4 inches of rainfall (locally) along the terrain on Tuesday, with precipitable water values of 1.00-1.25" and the chance for thunderstorms as low-level lapse rates steepen (and ML CAPE reaching perhaps as high as 500 J/kg). Areas along the coast and in the valleys will receive closer to an inch of additional rainfall on Tuesday, coming with an additional (final) surge of tropospheric moisture (and eventual cold front passage) in the afternoon.

We see just how much outside of the climatological norm this amount of rain and snowfall is 

Also rare severe thunderstorm Day 1 + 2 outlooks for California with tornado risks 

 

Brings my mind to this 

Ended up being an impressive bomb cyclone in the atlantic with a 51mb pressure drop in 24hrs

We continue to see the MJO phase 7 & SSW precursor pattern playing out 

 

There has been a taboo around displacement events being associated with failing in bringing cold and snowy conditions to the UK however this is misleading, interesting results from this paper

"Key Points

Little difference in the longer-term (3–4 weeks+) surface response in either free-running or thermally forced displacement and split events

Conversely, large differences are apparent between displacements and splits at shorter lags

Displacements yield stronger stratospheric temperature anomalies than splits yet still give rise to similar-magnitude tropospheric responses"

'For instance,  at 60 N and 10 hPa clearly shows a weaker vortex for the displacements than the splits'

A tonne of reading in it but an excellent study  

Just a moment...

AGUPUBS.ONLINELIBRARY.WILEY.COM

Google search - displacement stratospheric warming, its the first paper from 2021

More reason not to fear displacement events, again we see the clear link of strat warmings and Greenland blocking 

 

Images from a useful thread by James P 

Initially the current signs seem more toward a displacement (this could still see a split further down the line) taking the JMA which shows that nicely 

We currently have a bit of warming taking place 

And note how the PV gets shunted away from the Arctic southwestwards 

 

Oh did you think that was it... nah we have the next EAMT event shaping up too 

I did mention weeks 2-3 of Jan would be exciting

 

Very exciting times indeed I'll get onto that shortly

The snowpacks in the sierras are above levels we'd expect to see by APRIL!  

Looking like about a week more of Atmospheric river conditions before a switch in the setup, how can we tell that switch is likely? 

Again focusing on the Pacific Jet (top of image) similar to in my previous posts its still barrelling down on California 

*Also note the northwest > southeast alignment of our branch of the jet

But as we fast forward a few days we see the buckle and orientation shift in the Jet and a retraction west 

Looking closer at the conditions for the UK as we see low pressures aligned on the NW>SE Jet combining with 528 dam air this will see wintry conditions with showers of sleet and snow plus any fronts attempting to move across the UK into that air have great potential to deliver heavy battleground snow

Focusing on our Jet stream branch, we see an active jet streak 

Entrance of Jet Streaks

WWW.WEATHER.GOV

 

The one on Saturday looks very impressive

This will bring a large zone of 50-55mph gusts through Ireland, Southern Scotland and Northern England Tonight

More detailed chart of that developing storm 

Another develops hot on its heels through tomorrow and the start of the weekend 

This is a prime example of La Ninà MJO phase 8 through January  

Some more info on the Atmospheric River pattern before the most exciting part of my post

The first ever night tornado warnings issued by the Sacremento NWS area 

Stunning satellite views

Now the reasons for my excitement..

Nice MJO progression of phases 7/8/1/2

 

Here's the other setups associated with phases 8 + 1

 

 

 

 

Positive signs for a blocking pattern to set up and focus shifting to a flow from the East & NorthEast

Using my own personal method I'd expect those MJO Phases to begin transitioning into surface conditions from 23rd of Jan >>

Given Siberia is experiencing brutally low and record cold temperatures its definitely to be watched 

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787767

[Cold Winter Night]

This morning’s runs are have been a very welcome step in the right direction.
Especially the EC producing a promising Scandi High at Day 10 is encouraging.

I saw some this morning expressing concerns about those Low heights near Greenland. However, those are actually what got me most excited about the 240h chart.
It’s true, we usually don’t want to see that at all, but with a proper Scandi High and lower heights over S-Europe in place, a firm tPV is exactly what we need, a combination that has been lacking so far this winter, both in the output and in reality.

But what about “energy riding over the top”? Aren’t those Greenland purples an blues a very bad thing we want to avoid at all cost?
No, not in a Scandi High situation. To sustain the High, it must be fed with Warm Air Advection (WAA), and the tPV near Greenland provides just that. The Low heights over Italy will help set up  Cold Air Advection (CAA).

The one thing most legendary cold spells (1917, 1942, 1947, 1963, 1987 to name a few) have in common, is that very  Scandi High/W-Greenland Low setup in their beginning stages.
January 1917 is an example of this and that year is not unlike this year. Also La Niña. In De Bilt, the first 3 days of January were even milder in 1917 than this year. (Disclaimer: I use 1917 as an illustration, it’s not a forecast for next week).

The EPS regime chart shows the ensemble moving into the central circle as I yesterday suspected it would do. Extended output suggests it will move more toward +BLO, the upper half/upper left quarter of the chart.

We must remain cautious though, as the ensemble majority still has heights more over us, or to our East, than to our Northeast (still +BLO), but the wind chart for De Bilt shows more E/SE winds later on.

IMO, other models lately supporting something similar the EC Op, developing Scandi Highs on several runs give more weight to the direction of the high resolution run. It might be on to something.

Now, let's hope for the best (ensemble swing to Scandi High) and prepare for the worst (EC dropping this solution altogether) on the 12z.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787775

[bluearmy]

7 hours ago, alexisj9 said:

I think only the opp was updated, I don't know about the control, but the rest of the egfs were left as they were, would that include the control?

The control is part of the gefs - not upgraded 

4 hours ago, Daniel* said:

Watching GFS 00z roll out. I’ll admit I’ve never such low geopotential heights before modelled in U.K.. A piece of polar vortex, of course highly modified but surely widespread falling snow potential. Very intrigued to see the outcome of this.

Not even as low in December 2010… the only precedent I can think of, of course the pattern is not exact and there is not severe cold.

 

Bear in mind the 30mb slp difference which dictates the colours on the chart - the actual dam is very different 

2 hours ago, Daniel* said:

Very cold and slack, less exciting for snow potential. Unusual pattern with such low heights. 

Imo, the slacker the better for snow chances 

1 hour ago, joggs said:

Ahhh,the fabled day 10 chart....

There is plenty going on before day 10 ! 

1 hour ago, mulzy said:

This morning's GEPS and last night's EPS don't have such an extended period of cold so caution needed viz. the GEFS.  This morning's EPS also suggests a shorter duration for the *initial* cold snap.

 

With potential height rises to our ne, the uppers may not be that representative of the surface temps on a fair sized cluster of those eps 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787568

[Mike Poole]

ECM clusters for the 12z suite, T120-T168:

Lots of uncertainty here, and very relevant to the ‘will it snow’ argument.  The extent to which the high is held at bay is the thing, clusters 3 and 5 looking the best on that front.

T192-T240:

Variations on a theme of how the high moving through the UK might extend into scandi, or not.

T264+:

After all the uncertainty earlier, in the last timeframe it boils down to scandi high (26) or no scandi high (25).  Couldn’t be simpler!

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788017

[Nick F]

Quite the 00z EPS 500mb +height anomaly to our NE at T+300 

If anything, it creeps a little further west over Scandi by T+360, Atlantic trough kept a bay 

It is the means though, clusters will show more scatter of possible options.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787604

[bluearmy]

Having just looked through the strat charts for that run, it looks very interesting 

the strat ridge from the pacific side will push against the stretching vortex on our side of the NH  and we see the imprint on the final trop charts with a marked NH trop split.  The upper spv vortex is displaced over s Greenland by the end of the run but we see the lower levels of the spv stretched and with segments pushed towards Asia and ne Canada - the trop is able to actually build a griceland ridge at the end of the run. Of course it just a gfs op but it’s very promising to see that evolution. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4787737

[Catacol]

2 hours ago, s4lancia said:

9 SD ??

 

I’m sure it’s 6 but even so, that’s impressive.

Zoiks- now we are talking…. Just in from work and not had a chance to scan my pages yet beyond the usual NetW catch up but that’s one heck of a heat flux prediction. We know we have had a decent precursor pattern floating around for a while, and the energy in the pacific jet hammering California and dropping copious snow onto the mountains there may also be firing a huge amount of warmth up into the strat in the same motion.

As has been said already this evening, if the TPV starts to amplify as the vortex stretches and weakens then we don’t necessarily need a full SPW to land a reversed flow. A full downwell of negative anomalies is the most destructive of westerly influence but an assault as suggested in this graphic could be enough regardless of an end product SSW.

How exciting……! Must go pour over some more data…

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788088

[Cambrian]

That’s an enthralling 12z ECM op for a 10-day run slap bang in the middle of winter. 

It gets going as early as day 2, with colder air flooding south during the weekend. 

 

We’re really in business by day 4 with uppers of -6 degrees or lower for most parts, 

 

and still cold at day 6. Brilliant chart, looks like it could be a bit nippy around the Balearics. 

 

Briefly milder by day 9, but it’s a mere slither of mild air, getting pushed back in two ways:

 - Pushed back west by day 10 by a high moving northwest out of Russia into Scandinavia. That supply would be turning east of south at the surface over southern parts. 

  

- Pushed back in time (yesterday’s day 7 ensemble mean vs. today’s day 6 ensemble mean, deeper and longer lasting cold). 

 

We could end up with some very good chances - almost anywhere - of snowfall for a few days, followed by a few more under a ridge that are chilly on the ground, with the mild air not really getting in at the surface before the establishment of a Scandinavian high in time for the last week of the month.

The anomaly animation for the op shows the development neatly - our cold trough heads southeast into Europe, a bubble of heights from the west entices defection of heights west out of Russia to Scandinavia and the Atlantic never gets in. Temperatures on the ground could be really quite subdued throughout. A riveting run. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788114

[Met4Cast]

The airmass is cold but it's not quite cold enough. Wet Bulb Freezing level for example looks to be around 500-700 feet for much of England by day, although this does fall to surface levels by night. 

Persistent precipitation could allow for evaporative cooling to kick in lowering the snow level, but currently I think widespread accumulating snowfall could be a bit of a struggle. The usual caveat of features likely to appear at shorter lead times not withstanding. PM air is always a bit of a tricky one. 

Despite the 850hPa temperatures it appears to be quite a marginal situation & an incredibly tricky forecast re: what's actually going to fall out of the sky/where any precipitation will be. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788316

[Ladyofthestorm]

9 hours ago, blizzard81 said:

This event could very easily be a much shorter version of the December cold spell where very few of us saw any snow at all. 

We need the cold first and foremost. Precipitation will follow. 

The major difference this time around is direction this next cold spell is coming from .  Last time from a very dry continental flow.  This time around arctic maritime. 

 

I suspect precipitation levels will be nowcasted in many places. 

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788283

[feb1991blizzard]

 

BOOM!

 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4788369