Model discussion highlights

[chris55]

5 hours ago, RainAllNight said:

Do cold temps feel colder if the dew points are even lower?

Its essentially just dryer air.

The dew point is the stage where the air can no longer hold the moisture so it relents and the moisture gathers on solids, like dew on the grass.

In my experience cold dry air often feels less cold than more humid cold air.

Moisture conducts heat more readily than air, meaning a cold damp day feels colder than a day when the air is dry, but the temp is lower.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4799672

[knocker]

18 minutes ago, damianslaw said:

One of those situations where the models play variance but unusually it is UKMO at the opposite end, GFS as normal one extreme, ECM in the middle to an extent, the divergence taking place at 120 hrs, which is just about in the reliable. I would expect some convergence in the next 24 hours, but may take a couple of days. Will GFS back away from its strong ridge to the NE development, or will the UKMO do an about turn.

As often the case we tend to see a middle ground, and this would be high pressure ridging and building into the Uk anchoring east, ending with what some call the sceuro ridge, chilly but not the deep cold some may want, whilst it will mean often dry calm weather away from the NW.

I don't follow why the UKMO is relevant to the medium term solution as that rather depends of the movement of the tpv lobe moving into Greenalne post t156, resulting in a pumped up jet and amplification of the ridge north east across Europe. To my simple mind it is pinning down the energy flows around the subsequent Euro high and thus pinning down the detail is quite a headache and at this range and best treated with great caution

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4799780

[Cambrian]

The very positive indications up to around day 8 are clearly strongly imprinted across the GFS suite, not just the op. So if the op is out, then most of the pack is too. I understand that it was only the op that was modified in the update. 

The 12z GEFS mean now showing the same broad evolution that the heralding ops were showing just a couple of days ago, two waves of Azores heights now very confidently migrating northeast through the UK and Ireland to Scandinavia. It’s great to look at!

 

It’s the second wave of building heights that seals the deal, the positive anomaly over +30 resulting in a surface high that is located very close to the core height anomaly, over Scandinavia proper, instead of a good way to the south like we’ve seen a lot of modelling in recent months when the anomaly isn’t quite strong enough. This is all wrapped up in the prerequisites needed for the building and migration of a strong 1040mb+ high, a weaker high you feel would just have flopped into Central Europe.

This is a great pointer for me in knowing what to look for when chasing future Scandinavian highs, including what to look for across the ECM suite over the next few days. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4799773

[Kirkcaldy Weather]

1 hour ago, Battleground Snow said:

@Cold Winter Night @Singularity @Kirkcaldy Weather maybe some vindication for us.... 

 

 

 

There's a tonne of stuff unfolding thanks to these Indian Ocean phases, besides the blocking arriving within the models now, its having a huge factor in possibly bringing the La Ninà near its demise with a big Westerly Wind Burst across the Indian Ocean 

Bit of timing still to be worked out for the move to phase 4 with todays JMA keeping firmly in phase 3 even into week 2 of February 

Extended movement still could be promising for further fun by End of Feb + into March 

tho that's obviously for future focus, we've got enough to enjoy for the next couple of weeks 🌨🌨

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4799820

[Allseasons-Si]

I was reluctant to post tonight as it is getting on past 1am in the morning but as it stands,the gfs 12z and 18z and it's gefs ens suit is teasing us with this Scandi high and it's easterlies with all the other models in the medium term having none of what the gfs is showing

looking at the anomalies clusters etc just don't get there to my eye and look like a Scuro ridge with most of the cold heading into central SE Europe

we need these heights further north for us to benifit an undercut of cold air to our shores,...but i say this that there is a step in the right direction,the Scandi heights are growing stronger by day in my view but we just need a tweak further north then bingo,we have been here in this scenario many times over the years and we know how fickle it is to get cold into the UK

there is though growing support from the ECM de-built ens for an easterly(purple 70%) than yesterday's 35% so that increase has doubled but remember that this is for Holland and not the UK and that this easterly can stop short of the UK 

and finally whilst i prop my eyelids up with match sticks,...here is an ext'd look at the blocking formats from the NOAA,...retrograde to Greenland anyone,...yes please

G'night all

Oh! and it's heating up again uptop,...a cold easter perhaps,and would not be the first time,infact you are more likely to see snow around easter than the winter months.

op/control and mean...

that took 35mins of my time,...i do hope this cold spell pays off,...we all deserve it

and again i wish you all a G'night,...sleep well.

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4799929

[nick sussex]

4 minutes ago, Battleground Snow said:

GFS continues on its merry way, I've highlighted the difference to why the high can't get far enough north on the ecm

You can see the ECM spreads highlight the key areas . 

In yellow how far east the upstream troughing gets . In red the shortwave energy heading south and one parcel which is supporting the high .

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800019

[MattH]

Morning.

On full review of model data, the GFS still remains the 'least likely' option despite the consistency within itself.

Comparing and contrasting previous model 'wins' against up-coming events just won't lead to much success, GFS may well have correctly picked up the summer synoptics and heat, but that doesn't automatically mean it'll be correct with this setup either. The overall teleconnections still don't support a block to that extent, in that local. Think of a fishing swimming against the tide, that is what the GFS is currently doing. Clearly, the tide being the more dominant zonal, W'ly flow which the UKMO and ECMWF are bringing across the North Atlantic in time. It is always a very difficult task to push back against that flow, especially when there is such a deep, entrenched tPV now over NE Canada and Greenland, but it is the individual cyclonic wave breaks and short-wave details that will likely 'make or break' this outcome.

Overall, from last detailed post earlier in Jan, not much has changed - We all had to see what any strat developments would do, clearly not much. The outlook there does look interesting for late Feb/early Mar, one to keep tabs on, while the AAM remains firmly negative, but upstream changes with the MJO may well be on the way.

It is certainly a fascinating watch to say the least and, as has happened before here, one or more models will suddenly change and switch and, again, after complete analysis of the situation this morning then the GFS still remains firmly within the 'least likely' corner, while the UKMO and the ECMWF are more probable outcomes. Clearly, in meteorology just because it is 'least likely' doesn't mean it isn't impossible and those hoping for a more significant early to mid February cold spell, really from out of nowhere, have got to hope that the GFS has got this one correct.

Long-term and the key feature will be this potential warming in late Feb. The Scandinavian block coupled with the Aleutian low setup, as per GFS would likely 'do it', but how many times have we been here before, then having to trawl through synoptics in March and potentially April that nobody wants and of which would have been superb 8 weeks prior.

The joys of the British and NW European climate within an ever changing background due to AGW.

Cheers, Matt.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800067

[johnholmes]

The NOAA 500 mb anomaly chart frfom last evening continues with the idea of a ridge from Cherbourg to NE Norway and has the +ve anomaly of 210DM in the centre of the 500 mb ridge over Norway. Not that different on its 8-14 outlook. This is the 3 rd output from NOAA with a similar idea. Not often the 500 mb is much different in the 6-10 day scale on that basis.

Climate Prediction Center - 8-14 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800003

[Eagle Eye]

Reaction to ENSO modulated MJO Phase 3 by the looks of it with the Scandi +VE heights but how far north the Extratropical forcing can push it will be important of course. The tropical-extratropical interactions linked with the slowing down of the jet so +VE amplification via Kelvin Wave cycling is looking fairly likely but there's very little way of knowing how strong it'll be yet. This does favour the development of those shortwaves off the coast of Africa eventually pushing upwards and poleward forcing the Waves. Everything likes to be in balance and every reaction...well you know the rest. The importance of exactly how shortwaves to the south move cannot be underestimated here as they are an important tool for Kelvin-Wave modulation of the general feedback of the circulation of the exiting -VE EPO Wave that's taking place essentially now. As that pushes towards Greenland with the also exiting ridge pushing it towards the Greenland-BK region then it leaves space for the general circulation of a La Nina MJO Phase 3 to work a UK-Scandi high. That's all fairly set in stone. 

What isn't set in stone is how strong the atmospheric Ekman Pumping of the jet and the modulation of the initial UK-Scandi high. With good mid-Atlantic pumping we can get ourselves in what is essentially a cage but without good backing for that high I just don't see it moving in the right direction. So clearly, the handling of the North Atlantic needs to be very good and currently I don't know which model has got it. The initial setup looks fairly well handled but the strength of response to shortwaves and other factors will be the initial factor then the second pulse seems to keep it locked in according too the GFS but the ECM is showing something almost entirely different with weaker shortwaves and weaker amplification and a more transitory Wave.

GFS

ECM

For anyone interested, the ICON is sort of in-between the two and perhaps a more likely outcome.

The ARPEGE is similar

UKMO flattens the pattern out very quickly with little shortwave backing. Does anyone know how it tends to handle shortwaves as I think that's the problem here?

Clearly there's nothing set in stone and I wouldn't call one off just yet but I still think it's unlikely for now.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800119

[Mike Poole]

1 hour ago, Froze were the Days said:

Can you really compare Summer to Winter when it comes to modelling?... we all know reliability for forecasting is pretty solid out to 7-10 days plus ahead in the fore-mentioned due to such slow moving synoptics. When GFS forecast the hot spell how far out were we talking?, I do far less model watching post Winter

Actually, and maybe surprisingly, this is not correct.  The models are on average more accurate in winter than summer in the NH and this applies to all of them, going back years (top chart here):

This certainly doesn’t stack up with anecdotal evidence from watching the models on here!  But then, in both summer and winter, the types of synoptics that are of most interest are the exception not the norm (i.e. complex cold evolutions in winter, and slow moving anticyclone setups in summer).  What perhaps can be concluded is the models are more accurate for standard zonal fayre in winter than summer, and that is probably because in winter that sort of weather has the predictable behaviour of the vortex behind it, whereas in summer, it does not.  

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800152

[Catacol]

3 minutes ago, seabreeze86 said:

ECM 6z shows zero sign of backing the GFS 

...which is not a surprise. The passage of the MJO strongly through the IO supports the SE USA ridge and until it gets back to the Maritimes there is no connected support for anything to shift the Greenland/Icelandic low. Worth also showing these 2 graphics:

both of which show quite clearly that we are now slipping into an ocean/atmosphere connected La Nina state....and that means atlantic westerlies. No change to anything I have said about the first half of February ever since we failed to get a substantive impact from stratospheric disruption.

Things will change a bit in the second half of February. The MJO will come back around to phase 6/7/8 and given how active it has been this season I see no reason why it cannot continue in that same way. We will have the seasonal weakening of the vortex, indeed with the long wave pattern encouraging ridging in the Scandy sector and a north pacific that has surprised me this year and allowed more low pressure through the Aleutians - the EC long term forecast of another weakening of the strat vortex into the second half of February perhaps to levels that are significantly below the seasonal average also suggests something different.

It has been said by others....but in blunt terms: put together a strongish MJO into the West Pacific in later February alongside a weaker than average vortex and it screams a cold March to me. Is this a surprise? 2013, 2018 - the 2 snowiest months in the last 10 years and both were March. Something in the climate connections seems to be working to give more blocked and cold ends to winter for the UK and the last snowy February seems (and was?) an age ago now. 

Next year is looking like a possible eQBO/Nino combo which should get the juices flowing. For this year another unremarkable February, certainly for the first half, before things move towards the end. Timing is always a pig - could a pattern shift occur in the final third of February? Yes - possible. But these things always seem to take longer than expected so my money would be on early March.

 

 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800142

[Daniel*]

FYI in recent days at day 5 the GFS has had a rally in performance whilst most have nosedived, second to ECM.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800305

[Blessed Weather]

1 hour ago, Eagle Eye said:

Reaction to ENSO modulated MJO Phase 3 by the looks of it with the Scandi +VE heights but how far north the Extratropical forcing can push it will be important of course. The tropical-extratropical interactions linked with the slowing down of the jet so +VE amplification via Kelvin Wave cycling is looking fairly likely but there's very little way of knowing how strong it'll be yet. This does favour the development of those shortwaves off the coast of Africa eventually pushing upwards and poleward forcing the Waves. Everything likes to be in balance and every reaction...well you know the rest. The importance of exactly how shortwaves to the south move cannot be underestimated here as they are an important tool for Kelvin-Wave modulation of the general feedback of the circulation of the exiting -VE EPO Wave that's taking place essentially now. As that pushes towards Greenland with the also exiting ridge pushing it towards the Greenland-BK region then it leaves space for the general circulation of a La Nina MJO Phase 3 to work a UK-Scandi high. That's all fairly set in stone. 

What isn't set in stone is how strong the atmospheric Ekman Pumping of the jet and the modulation of the initial UK-Scandi high. With good mid-Atlantic pumping we can get ourselves in what is essentially a cage but without good backing for that high I just don't see it moving in the right direction. So clearly, the handling of the North Atlantic needs to be very good and currently I don't know which model has got it. The initial setup looks fairly well handled but the strength of response to shortwaves and other factors will be the initial factor then the second pulse seems to keep it locked in according too the GFS but the ECM is showing something almost entirely different with weaker shortwaves and weaker amplification and a more transitory Wave.

GFS

ECM

For anyone interested, the ICON is sort of in-between the two and perhaps a more likely outcome.

The ARPEGE is similar

UKMO flattens the pattern out very quickly with little shortwave backing. Does anyone know how it tends to handle shortwaves as I think that's the problem here?

Clearly there's nothing set in stone and I wouldn't call one off just yet but I still think it's unlikely for now.

Just thinking out loud about your opening remark EE. On the assumption the MJO Ph 3 (not usually helpful to a cold synoptic pattern for our neck of the woods) has been helpfully 'distorted' by La Nina suppression and is behind the attempts at a Scandi High, then I wonder if the fact that ECM performs best with Phases 1 to 4 forecasting, whilst GFS performs best with Phases 5 to 8, is behind the current discrepancy between the model forecasts?? Of course this may be nothing to do with the current model differences. And it should also be noted that the research influencing my thinking out loud was published in 2011, but it did make me wonder if it might be influencing the current situation. Research extract:

ECMWF has the best skill for the initial phases 1–2 and for phases 7–8 in the latter half of the forecast. In particular, ECMWF initialised at phase 1, which is generally valid in phases 1–4, shows the lowest RMSE [error] compared with initialisation in the other phases, whereas the other centres tend to show larger RMSEs for initialisation at phase 1 than at other phases. Among the centres, ECMWF shows superior skill regarding the MJO phase, although the MJO amplitude predicted by ECMWF is larger than that observed. An eastward propagation of the active MJO from phases 1–2 appears to be well predicted by ECMWF, but not by the other centres.

Source: Verification of medium-range MJO forecasts with TIGGE

 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800167

[nick sussex]

Although the GFS 18 hrs run gets there with the Scandi high the early stage isn’t so clean in terms of evolution in the key area Iceland to Svalbard .

And this is a warning sign re what the other outputs have modelled in that area .

Hopefully there will be a resolution in the morning .

Before then for those still awake there’s the ECM 18hrs run to T90 hrs and control runs to T144 hrs . 

Will they show any interest in the GFS solution ?

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800502

[blizzard81]

Just thought I would add this to the mix. Latest fax chart at T96 for Sunday compared to yesterday's T120. You can clearly see the better ridging of the high north east on the T96 compared to the T120 from yesterday. Hmmmm! Oh.... Also nearly forgot to mention that Denmark shortwave on the updated T96 that wasn't there on yesterday's T120. A definite move towards gfs there. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800593

[nick sussex]

Not sure if people are aware but the GEM also has an 06 hrs run which runs to T84 hrs . Given the crucial early timeframe that might be worth a look. It’s available for the Europe area only and you can find that at Meteocentre .

I only discovered that last night !

 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800755

[Eagle Eye]

I'm not going to get bothered over which model is correct at the moment but it's clear that at a longer range the Scandi block has a decent favour in a La Nina MJO Phase 3 and it is linked with the Anticyclonic Wavebreaking (AWB) at the relative 'exit' of the Atlantic jet. Normally with a stronger Strat Vortex coupling downwards but this is where the initial very weak Vortex has inadvertently helped us even without coupling downwards so the warming wasn't useless. I think the -VE EAMT retracting the Pacific Jet also helped us as it allowed a relative Rossby Wave train enhancement given how the -VE EPO acted and that was important when combining with the shortwaves and Kelvin Wave linked with -VE velocity potential that are helping to push that Scandi high just a little bit more.

You can see that we are at the Atmospheric River stage likely with a train of moist air but importantly it's slightly further North and weaker likely due to the weaker jets than typical feedback as the SE US ridge was in place. You can see that this setup is typical of a La Nina MJO Phase 3 but with some good differences. Is it good enough though?

According to the GFS 00Z, the initial movement is for the combination of previously mentioned factors displacing the cold pool slightly and +VE heights push from N UK to N Scandi and then the buckling of the Atlantic jet with AWB (two areas of AWB with both Scandi and Greenland seems unlikely to me?) and that's what locks the cold in place very well and also the placing of the +VE heights is why we get the cold in the first place.

The 06Z appears to have backtracked slightly but that doesn't mean it can't re-pick up what it was seeing before as it isn't a trend for now. Though the other models seem to be showing it more like this. This is sort of the middle ground and perhaps what is more likely with not a beast but still surface cold and the south being favoured.

Whilst most other models aren't showing it to quite this strength it does show that it's possible.

So I don't subscribe to the "GFS is 100% wrong here and I'm right because I went with the form horse of Winter" group. Sure they're probably more likely given the trend but I don't see why it couldn't be correct in this situation and has some backing. It's not the most likely outcome imo but it's a fair chance. Would hate to bang my own drum after telling others off for doing that but I said this on the 19th though I did get the Ural part wrong. Also most of my predictions before this part were 50/50 and I didn't really mention the scale of timing either...

"The retrograde Scandi-Ural high will be an interesting one to watch for surface warmth developments over Scandinavia and the displacement of the cold as that'll affect where the cold is centred, interesting for gaining cold from different areas such as the South."

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800824

[nick sussex]

Quite a big jump in the GEFS in terms of 850s .

Far removed from the earlier 00hrs . The GFS did get something’s right , the other models originally wanted to take low pressure east towards Norway .

As it transpired this was wrong , and the low phasing with the PV as called by the GFS and shortwave energy heading ne was correct .

Of course it will face derision because of its later output but let’s not think that the Euros and other models were right all along .

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800839

[Cold Winter Night]

The GFS bashing is getting a bit ridiculous in here.

The GFS option with a High further North over Scandinavia, and CAA pulling cold Southwest has been present in more or less all the ensembles, so the GFS Op has never been alone in showing it.

And let’s go back in history, all the way to Monday, January 30, 2023.
Yup, that’s just three days ago, everyone should be old enough to remember it.

What did the Supermodels ECM and GEM show for –then Day 10- Thursday the 9th?

EC: Massive High over Scandinavia/Russia, Low Mediterranean heights.
GEM: Massive Scandi High, Low Low SE European/Mediterranean heights.

And what did the "Rubbish/Cannon Fodder/Only fools look at it/Let’s ignore it" –model GFS show?

GFS: Mid latitude Euro Heights, with only moderately low heights to the South.

Well, this is awkward, I spy the middle ground solution! On GFS.
Yes, GFS at Day 10 was closest to what is now considered the most likely outcome (which has not yet happened btw).

So, are EC and GEM cannon fodder too? Of course not, and neither is GFS.

I think a big problem in here is that 60% or 85% probabilities are casually rounded off to 100% and 40% or 15% probabilities are rounded off to 0%.
It annoys me when operationals or ensembles show unusual synoptics, especially at short lead times (like GFS just did) that some posters dismiss it as “0% chance of that happening.” Well, if it was 0% it would not be shown.
Just be accurate and fair. It’s not as black-and-white as we would like.

And, @MATT TATTOO just mentioned it too, let’s not evaluate before the thing has even happened.
Verification stats can be useful, but not to evaluate the likelihood of single model runs verifying.
Just because a model has slightly worse stats on average does not mean you can dismiss the present forecast. The most recent run might be a model’s peak performance or its worst show, and that goes for EC just as much as for GFS.
You don’t know in advance, only in hindsight.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800929

[nick sussex]

The set up is somewhat complicated by the response of the troughing to shortwaves phasing at the base.

You can see that here on the ECM 06 hrs control run. The shortwave runs east as it phases you get an anti clockwise effect on the troughing which gets thrown ne on its eastern flank . This then allows a pulse of heights ne. You can see the energy movement below .

So T120 hrs.

Then T144 hrs.

This alters the orientation and placement of the high centre so if there’s any colder pooling on the southern flank this could get pulled back in towards the UK.

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800928

[nick sussex]

I’m wondering whether this is a data issue perhaps re observations in that area .

There is a lack of conventional observational data above 70N.

You have good satellite coverage there but lack other observations. I don’t think we’d be seeing this stand off if the area of contention was further south.

I’n shocked that this drama has continued overnight ! 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4800705

[Uncertainty]

The U.K. high —> westerlies —> big time blocking take for Feb into March I and others have been plugging is still on track. 
 

The first brick in the wall is nailed on. The gfs has been more right than the euros on this, but obviously the op took it too far (the dodgy new upgrade clearly over-amplifies). 

 

The westerly phase also looks well supported. The big three in mid Feb look ++nao

 

The mjo passing through p4 is, for me, our most ‘westerly’ phase, even in a Nina.

By the end of Feb though, as the now highly supported strat warming effects kick in and the mjo departs P4, we are looking at a blocked, possibly severe March.

 

The 15-18th Feb looks like the landing point for this next warming and it looks more likely to make it as a major ssw than the milder version we had recently.

CFS is really keen on a 2018 style high amp P6/7 push. Eps less so but same direction.

The early projections from the 46 for March are only illustrative, but a spell of blocking is the logical outcome to the strat/mjo progression.

 

 

Whether we ‘like it’ or not, This is the way the cards look to have been dealt. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4801210

[carinthian]

18 hours ago, carinthian said:

As promised a bit of an update.  Snowfall predicted to be quite prolonged and intense over the the period Thus-Mon.  The fine mesh model predicts 85cm in this period, which is a lot of fresh snowfall and if that turns out to be correct will cause quite a few problems in the mountains. A series of weather fronts during this period are expected to straddle the Eastern Alps along the developing NWly jet combining with plenty of moisture in to the lower layers that will enhance the likely hood of some extreme snow conditions. By Tues the frontal systems will slowly decay as a cold pool develops over the Northern Alps and Southern Germany.  Obviously any CAA towards the UK will require the build of ridging of high pressure further NE into Scandinavia combined with the retention of lower heights over Europe.   Maybe in the next 24 hours we will be a bit wiser as to which type of colder weather will encroach the British Isles.

C

Morning all. The big snow threat continues for the next 3 days. Computer snow forecasts show another 40cm of fresh snow to fall  before high pressure takes charge with sunny conditions to prevail from Tuesday on wards. Some pictures of the recent snowfall are shown on the Austrian thread this morning.  The snow train is a continuous feed of lower level moisture along  an extended  convergence zone aligned down the North Sea into Germany and drops massive snowfall at elevation. The snowline is expected to drop significantly to 400m by Monday. The models this morning in the extended period seem to show a huge block of cold surface air getting established over much of Europe  with Southern Britain tapping into some of this. Tracking pools or formation of colder upper air is always hard to determine in this type of set up. However, be prepared for some unexpected developments around days 7-10. So looks like becoming drier and a fair bit colder for many early next week.

C

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4801346

[bluearmy]

The eps mean is within a nats of a ssw by day 15.  Sadly no way to see how many members are actually reversed and how many are split 

the gfs 06z reverses again - with the eps added , looks pretty certain that we will see an ssw by the end of week 2 (although the gefs aren’t showing a mean reversal although we can see how many members are reversing (60%). 

what we should be looking for now is QTR signatures at the back end of gfs ops and eps control runs.  Look for a sharp ridge driving from the n pacific into the pole and driving a big neg AO. 

as Mike pointed out yesterday, the flushed down westerlies from late jan mean that we would expect less resistance to this reversal downwelling.  Whether ne europe is a wintry beneficiary of this currently unknown. If there is no QTR then we would still expect to see several downwelling reversal waves affecting the trop through march and April. Again, would our part of the NH be affected ??

there is enough evidence that this ssw could well be a split of some kind - remnant segments over Asia and somewhere in the Atlantic with the Asian segment the larger and hopefully the one to our west dissipating. 
 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4801395

[Eagle Eye]

Interesting look to the Strat Wavebreak structure on the GFS and it really forms a well displaced Vortex which shrinks a lot and despite it only being Wave-1 the forecasts seem to suggest that the Vortex essentially wants to split as if it's had enough of the warmings with the thermal transfer so far away from the Acrtic. It appears to remain fairly barotropic but the displaced barotropic motion is quickly losing it's background help with the polar-night. So absolutely no polar-night jet and a thermally unbalanced gradient + a displaced Vortex appears to be a good sign. 

The backing for barotropicity (likely not a word) without the 1st Ekman velocity for rotary/stable flow - which in the case of the Winter Stratosphere would be the polar-night jet which arises from a strong Trop-Strat temperature contrast within Winter and forms the strong westerly momentum that coldies don't like - becomes slowly more Baroclinic leading to the '2nd Ekman' force for increased pressure-gradient change away from Barotropic stability. Essentially, the further away from the initial pressure-gradient balance, the more the fluid attempt to recover itself by going in the opposite direction to return to stability with the 'escaping' Baroclinicity.

A little bit about Barotropic/Baroclinic fluids and instability (from Treatise on Geophysics (Second Edition), 2015 and other sources/ my general ramblings about it);

A Barotropic fluid following the density-isobar quasi(near)-constant and the norm for Strat and Trop behaviour. When unstable, it tends not to like it and we see non-typical heat and cold movement. For example a displaced or split Strat Vortex or a decidedly 'non-zonal' Trop pattern though it's more when there's largely abnormal quick heat transfer baroclinically (we'll go over that later in this post) due to a stronger thermal gradient within the fluid. A Barotropically stable fluid is fine where it is and will be able to balance out anything that isn't strong Baroclinic.

What about a Baroclinic fluid? Well, these are more interesting. As that's when the gradient of the isobar-isotherms and heat distribution is more gradient based. So the pressure-heat balance has a decidedly more contrasted look to it in the fluid and that's important for getting a temperature contrast. Temperature contrasts help with the formation of Baroclinic Eddy's and as I've said before Eddy's are what transfer poleward heat and a Tropopause 'kicker' of the Stratosphere circulation and Wavebreaking that can potentially lead to a SSW. Essentially it's what helps to transfer planetary scale heat, momentum and energy flux into the Stratosphere and is why a Barotropic Trop rarely appears to lead a SSW.

Some more reading on Eddy's.

https://doi.org/10.1175/JAS-D-21-0262.1

An interesting laboratory experiment on how Baroclinic Eddy's act and you can see the beauty of fluids such as our atmosphere.

 

I think the GFS run is unlikely but we'll see how we go.

That's enough about some early fluid theory for now. Might go further in-depth later today.

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4801451