Model Output Discussion - A cold start to Spring?

[Catacol]

4 hours ago, bluearmy said:

The dp’s are generally fairly borderline where the main precip occurs so I wouldn’t be certain that we won’t see more of a slush fest than a winter wonderland away from >400 feet.

its very tricky  

Yes. Don’t be dazzled by the pink. This setup is very marginal and parts will see rain or sleet - possibly many areas. There is likely to be a sweet spot that is impossible to identify even at this short range that will see a good snowfall for a time - but my instincts looking at the charts and the daytime temperatures are that this is a scenario where people are best to set the bar pretty low and then if you are in one of those fortunate areas where the conditions click be pleasantly surprised. Expecting this setup to deliver widely in terms of an all snow event that will stick and survive I think might lead to widespread cursing. I’ll be interested to see tomorrow if the Met turn any of the warnings amber because so far they are clearly not convinced of significant impacts and have left everything yellow. The media are fanning the flames - even the moderate minded BBC were getting all excited on the news - but I can see a lot of mixing going on given the angle of the Atlantic attack and it might end up being a scenario where experience trumps models.

Hope very much to be proven overly pessimistic still.

The overall pattern sliding away as the block hotfoots to Canada. I would not have expected this ridge to be so quick to retrogress and collapse when looking at the shape of things at the start of the month but without the vortex split perhaps it was naive to expect a -AO to hang around for long.

Bring on 2023/24….winter of eQBO, Nino and the dramatic late December split.

[Geordiesnow]

I think that is a good point in the post above, there be some who will see snow but it won't lay because its too wet, some will see sleet and on the GFS especially the gradient is pretty tight so you could quickly see snow turning back to rain and then vice versa as the cold air tucks back in again.

 

 

 

 

 

 

 

[kold weather]

11 minutes ago, Catacol said:

Yes. Don’t be dazzled by the pink. This setup is very marginal and parts will see rain or sleet - possibly many areas. There is likely to be a sweet spot that is impossible to identify even at this short range that will see a good snowfall for a time - but my instincts looking at the charts and the daytime temperatures are that this is a scenario where people are best to set the bar pretty low and then if you are in one of those fortunate areas where the conditions click be pleasantly surprised.

I think tonight is probably a banker at this point, especially given the timing negates several of those very marginal factors and the front looks legitimately strong at the moment. Its obviously not going to last long but I suspect it may end up overperforming the models, I've seen several of these types of situations give higher amounts than you'd expect.

I think the concerns you have are warranted, especially on Thursday as the milder marginal stuff moves up. I wouldn't be surprised if it is a wintry mix lower down, whilst in the higher grounds like the pennines they get pretty huge totals. 

I think the main thing to watch will be frontal strength. so to speak, the hotter it comes in, the greater the chances that evaporative cooling will overcome the issues you mentioned.

I also think its telling that normally conservative/realistic models like ICON/AROME when it comes to snowfall accumulating are giving pretty widespread snow at various points.

PS - watch the formative El Nino end up becoming top end moderate/strong just to screw us over! I think a weak-low end moderate El nino could be very interesting, especially as historically that tends to be the bullseye for lowest -ve NAO figures for winters (somewhere between +0.8 and +1.2)

Edited March 7, 2023 by kold weather

[Man With Beard]

58 minutes ago, Allseasons-si said:

Harmonie vs the latest radar and again the short range models are struggling with the NE extent of the ppn in the southern irish sea.

this for 10pm.

a lot could have surprise snow fall on there dorstep in the morning.

Currently ARPEGE 18Z is bang on the radar for right now. Harmonie not bad. AROME is miles out.

Oh and to add to @kold weather, absolutely, once a strong front is guaranteed then projected precipitation totals are slightly pinch of salt, 20mm forecast could lead to anything 10-30mm, we don't tend to notice with rain but happens all the time.

I'm getting pretty confident there will be disruption by the morning on higher routes in the south e.g. A3 Hindhead, and further north as the day goes on.

Edited March 7, 2023 by Man With Beard

[Catacol]

19 minutes ago, near northampton said:

Scandinavian Highs are as rare as Rocking horse poo, yet they are seemingly mentioned wished for hopecasted several times daily in this thread, do you know the last time there was such a feature? I don't suspect several years ago

Greeny/Scandy perfect sausage 2018

More conventional, traditional Scandy block from the epic week of 1987. But you are correct - perfect Scandy Highs are rare. 

 

[A.J]

for those model enthusiasts who love a bit of indepth analysis, the key number to remember is 3150

anything less and its a damp squib washout, hitting that magic number or even better, then its a guarenteed snow fest !

what is this number and why is it significant I hear you ask ?

This is simple, its the amount of exclamtion marks Sheiky has used in the past week in this thread

Edited March 7, 2023 by A.J

[Battleground Snow]

23 minutes ago, Mapantz said:

ARPEGE snow chart:  Warning: does not represent the final layer on the ground, does not take into account settlement, melting.

Yes it's a good point which was touched upon earlier this afternoon,

The only areas likely to reach shown amounts are areas above 250m

I find arome tends to be able to pick out the elevated parts quite well 

Attached is only up to 51 hours so, doesn't include Friday mornings totals, but it's probably more representative compared to the arpege.

Regarding amber warnings, I think they would be warranted- because  the areas under heavy evaporated cooling could become quite treacherous in a short space of time, especially the road network.

 

Edited March 7, 2023 by Battleground Snow

[geordiekev]

10 minutes ago, Catacol said:

Yes. Don’t be dazzled by the pink. This setup is very marginal and parts will see rain or sleet - possibly many areas. There is likely to be a sweet spot that is impossible to identify even at this short range that will see a good snowfall for a time - but my instincts looking at the charts and the daytime temperatures are that this is a scenario where people are best to set the bar pretty low and then if you are in one of those fortunate areas where the conditions click be pleasantly surprised. Expecting this setup to deliver widely in terms of an all snow event that will stick and survive I think might lead to widespread cursing. I’ll be interested to see tomorrow if the Met turn any of the warnings amber because so far they are clearly not convinced of significant impacts and have left everything yellow. The media are fanning the flames - even the moderate minded BBC were getting all excited on the news - but I can see a lot of mixing going on given the angle of the Atlantic attack and it might end up being a scenario where experience trumps models.

Hope very much to be proven overly pessimistic still.

The overall pattern sliding away as the block hotfoots to Canada. I would not have expected this ridge to be so quick to retrogress and collapse when looking at the shape of things at the start of the month but without the vortex split perhaps it was naive to expect a -AO to hang around for long.

Bring on 2023/24….winter of eQBO, Nino and the dramatic late December split.

Think we just got unlucky, longer term, as there was no US systems to prop the E & W USA blocks in place, which in turn are just eeking the trop PV back into it's usual positions.

Though from a glass half full perspective, we've been lucky just to get in this position but may well be last chance saloon, so best of luck this week.

Will the volatility in the mid terms continue but seems they are settling on the return to norm, so perhaps Spring not that far away

[Mucka]

UKMO 18z looks pretty far S

[January Snowstorm]

12 minutes ago, Mucka said:

UKMO 18z looks pretty far S

Where did you find that?

I didn't know ukmo do an 18z

[Cheshire Freeze]

25 minutes ago, Catacol said:

Yes. Don’t be dazzled by the pink. This setup is very marginal and parts will see rain or sleet - possibly many areas. There is likely to be a sweet spot that is impossible to identify even at this short range that will see a good snowfall for a time - but my instincts looking at the charts and the daytime temperatures are that this is a scenario where people are best to set the bar pretty low and then if you are in one of those fortunate areas where the conditions click be pleasantly surprised. Expecting this setup to deliver widely in terms of an all snow event that will stick and survive I think might lead to widespread cursing. I’ll be interested to see tomorrow if the Met turn any of the warnings amber because so far they are clearly not convinced of significant impacts and have left everything yellow. The media are fanning the flames - even the moderate minded BBC were getting all excited on the news - but I can see a lot of mixing going on given the angle of the Atlantic attack and it might end up being a scenario where experience trumps models.

Hope very much to be proven overly pessimistic still.

The overall pattern sliding away as the block hotfoots to Canada. I would not have expected this ridge to be so quick to retrogress and collapse when looking at the shape of things at the start of the month but without the vortex split perhaps it was naive to expect a -AO to hang around for long.

Bring on 2023/24….winter of eQBO, Nino and the dramatic late December split.

Just a point on the Metoffice warning for Thur/Fri- it’s only yellow because it’s at maximum uncertainty. It’s at the highest impact level it can be.

[Mucka]

8 minutes ago, January Snowstorm said:

Where did you find that?

I didn't know ukmo do an 18z

You can get it on Wetter. If you take the time stamps then it would equate to UKMO 12z 60hr chart for comparison I think (taking off 1 hour UK V EU time)

Adjust the advance time to 6hr steps.

Wetterzentrale - Top Karten - UKMO EU Europe 18Z

WWW.WETTERZENTRALE.DE

---

Wetterkarten UKMO EU Europe 18Z

 

Edited March 7, 2023 by Mucka

[ukpaul]

14 minutes ago, Mucka said:

You can get it on Wetter. If you take the time stamps then it would equate to UKMO 12z 60hr chart for comparison I think (taking off 1 hour UK V EU time)

Adjust the advance time to 6hr steps.

Wetterzentrale - Top Karten - UKMO EU Europe 18Z

WWW.WETTERZENTRALE.DE

---

Wetterkarten UKMO EU Europe 18Z

 

Is that the same as the UKMO HD on Meteociel?

WWW.METEOCIEL.FR

---

Meteociel propose de manière régulière le modèle à maille fine UKMO 0.1° du UK MetOffice (météo angaise) sur 5 zones (France, Nord-Ouest, Nord-Est, Sud-Ouest, Sud-Est et pays limitrophes)

 

[Rain All Night]

39 minutes ago, January Snowstorm said:

Where did you find that?

I didn't know ukmo do an 18z

Meteociel does have the short 6z and 18z runs but for some reason only has country-specific charts for these.

Meteologix seems to have all the global output from these runs, but its charts are quite different to what we're used to.

Edited March 8, 2023 by RainAllNight

[Eagle Eye]

I'm going to have a look back at how I did for now as I'm too in love with a girl to get mixed up in the will it and won't it snow stuff .

February 15th

"

This time, the SE US ridge might work in our favour without a -VE EPO so strong and no exiting wave of warm air meaning that the lag in about 10 days plus with a quite strong phase 5-6 lag suggests a much better North Atlantic and perhaps Pacific signal as well. So more poleward advection of energy transport and with that comes Rossby Waves carried by the eddies.

To put it bluntly, the first SSW is unlikely to affect surface temps however the second warming might be able to downwell easier. Looks very much to me like were probably seeing the uncertainty of if the first SSW can affect the Troposphere at all and the lag of the MJO movement rather than the direct affects itself yet. 

I feel like this will get pushed back till the second SSW time as the models start to model the zonal wind structure throughout the atmosphere better when it gets closer to time. Essentially this is a learning curve with so much going on and of course the poor modelling between the Stratosphere and the Troposphere. We've also got to be careful of conformation bias when looking back at how this eventually worked out as I think this could be a good event to look back on to understand everything."

February 25th

"Looking at the background signals and everything is lining up fairly well for early to mid March for now as the general signal for the best transfer of momentum via mountain torque temperature. Heat over the Himalayas so upwards wave transfer of momentum into the Strat and circulating into the Trop also exciting a Rossby Wave packet which breaks cyclonically and extends the Pacific jet but also the Tropopause to Strat part of the Wave could really help bring down the SSW quicker than expected."

February 28th

"Secondary large +VE EAMT likely to cause extension of Pacific jet and cyclonic wavebreaking over North America which is typically good for North Atlantic jet retraction and blocking towards Greenland via RWT induced AWB enhancement.This could potentially form a dipole of blocking to the North. Given MJO staying fairly enhanced in a weakening -VE ENSO state MJO Phase 7/8 with the start of the westerly wind burst into the climbing -VE Nino 3.4 area. Given a cycling more west based -VE EPO cycle and an E US ridge then we could have more chances for cold events up to mid March. Relying on strong MJO Phase and the atmospheric state to remain in the intraseasonal Nino state band (+VE AAM) and w'ly atmospheric drag which cycles around certain areas depending on the RWT. Tropical forcing looks to remain high for now though given the MJO RMM staying around Phase 7-8 and around +2 in terms of RMM 2 strength and mountain torque events. So Wave propagation and jet oscillations suggest zonal wind recovery is unlikely with the mean transport of mass, momentum and energy given the transfer of w'ly momentum via tropical-extratropical interaction under this Nino setup. Frictional torque is likely to repress the mountain torque gain and cause a -VE EAMT event but the SSW appears to suppress that reaction for now."

I think overall I did quite well but I was too excited about the second chance to properly mention this one which is looking to be much better than any chance later into March though this is from the second part of the SSW downwelling and MJO excitement with Tropics momentum and convection modification. The Nino modified w'ly eq-lat with Rossby Wave dispersion events leading to better MJO CCKW modification between tropics and extratropics for RWT events in the meridional circulation. With the extension of the Pacific jet, the energy and momentum changes between Eq-lat and the Tropics dynamically shifted. Imagine a scenario (in a Global Synoptic Dynamic Model (GSDM) ) where you have a w'ly momentum bands exchanging energy up from the lower tropics and it's induced by a large double +VE EAMT which retracts the Pacific jet. That frictional-rising AAM double response between the two to balance out the laminar flow in the atmosphere as a fluid flow tends to do (despite inertial forces tending to dominate and a strong jet stream favoured above boundary layer area, the viscosity and resistance of a fluid to being misshapen helps with the development of that RWT) helps with southerly jet push and the momentum fluctuation in the jet back up towards the north in the form of a Rossby Wave. The setup in this situation happened to favour North Atlantic AWB with a retrogressing Greenland-Scandi dipole that eventually let's our best angles cold flow fall eventually as the energy is transferred towards the Alaska area of the Rossby Wave.

Enjoy the snow if you get it you all.

[Mucka]

15 minutes ago, ukpaul said:

Is that the same as the UKMO HD on Meteociel?

WWW.METEOCIEL.FR

---

Meteociel propose de manière régulière le modèle à maille fine UKMO 0.1° du UK MetOffice (météo angaise) sur 5 zones (France, Nord-Ouest, Nord-Est, Sud-Ouest, Sud-Est et pays limitrophes)

 

It's possible, but the charts are in a more familiar format for comparison with other models and UKMO 12z.

Short answer, I don't know.

[Bricriu]

1 hour ago, geordiekev said:

Think we just got unlucky, longer term, as there was no US systems to prop the E & W USA blocks in place, which in turn are just eeking the trop PV back into it's usual positions.

Though from a glass half full perspective, we've been lucky just to get in this position but may well be last chance saloon, so best of luck this week.

Will the volatility in the mid terms continue but seems they are settling on the return to norm, so perhaps Spring not that far away

Well that's a bit disappointing, as the UKMO was showing a good Northerly for early next week, and the GFS was showing it cold again after mid month. I thought with two warmings  in the strat that there would be cold spells throughout March. So to now hear we are going back to normal  is not good news. Still, if Thursday and Friday deliver, I can live with a return to normal fare. 

Edited March 8, 2023 by Bricriu

[Battleground Snow]

ECM 18z with a small shift north for Thursday/Friday, still not as far  north as the GFS.

Goodnight 

Edited March 8, 2023 by Battleground Snow

[WillinGlossop]

45cm- 35cm southern Pennines looking interesting on models

hopefully Somerset picks up some good accumulations overnight… looks good on radar… 

5-10cm around Taunton going from latest model runs… 

hopefully firm up a little tomorrow and met office updates

 

[Cheshire Freeze]

23 minutes ago, Battleground Snow said:

ECM 18z with a small shift north for Thursday/Friday, still not as far  north as the GFS.

Goodnight 

Yes, heavy snowfall across N Wales, N mids and N England Friday morning-

It doesn’t even look especially marginal on this run either-

[Andypvfc]

8 minutes ago, CreweCold said:

Yes, heavy snowfall across N Wales, N mids and N England Friday morning-

It doesn’t even look especially marginal on this run either-

Anyone give me an idea of rough timescales. Friday 2am I've got a run from Alsager to Man Air

[Mark wheeler]

Is this accurate? I know it's the middle of the night.  Radar shows a very story but no feedback. Models show front entering south west and further.

Edited March 8, 2023 by Mark wheeler

[Mucka]

6 minutes ago, Andypvfc said:

Anyone give me an idea of rough timescales. Friday 2am I've got a run from Alsager to Man Air

Looks like, based on ECM 18z, main ppn hits NW England around 3AM and continues through to around 9AM.

It may be it is quite a messy affair for Manchester area with light sleet turning to rain or snow to sleet and back again as the cold air gets pushed N Thu night in Friday before retuning S in the early hours.

Local areas could vary quite a lot with favoured spots havign all snow and heavier ppn and less favoured spots seeing a wintry mix and lighter ppn.

In my experience NE Manchester does best and SW Manchester the worse in these situations but this info could be out of date in a few hours!

[sheikhy]

24 minutes ago, CreweCold said:

Yes, heavy snowfall across N Wales, N mids and N England Friday morning-

It doesn’t even look especially marginal on this run either-

That looks lush for pretty much all of wales the midlands and north england🌨🌨!!

[lassie23]

Please correct south fgs