Model output discussion - proper cold spell inbound?

[snow freak]

22 minutes ago, TheBeastFromTheEAST said:

Hi Teits , hope your ok? Always loved you posts as they are always good to read and easy to understand. ( The Eye in the Sky) i think you used to be called many years ago.

 

Anyway moving on, its looking like the middle to 3/4 of the way now through feb before hopefully we finally see some PROPER SNOW.... My question to you or anyone els  is will it be a struggle to keep snow around long on the ground as its getting closer to the end of winter come 3/4 of the way through Feb.. And this isnt a end of winter post by the way lol.. thats why im asking this question. 

 

As im sitting here now in the sun in my garden sheltered from the breeze its actually feels plesant and dare i say it i can feel some heat in the sunshine down here in Kent. Lovely blue skies.... But give me snow anyday.

 

Thanks ?? 

i don't think the fact it is February decreases the chances of lying snow even for a number of days if the conditions are right.  March 2013 saw a good snowfall with the snow hanging around for a few days because the conditions were perfect.  We can get snow in the very depths of winter but it can also melt straight away or only stay around for a day or so before it melts purely because the conditions are not right.  I think we sometimes put too much emphasis on needing snow in December and January thinking these are the best months but in reality February and March are probably the best months even if the sun is slightly stronger than in the other 2 months and the days are getting longer.  Just because the days are short and sun is lower in the sky doesn't necessarily mean its a guarantee of snow and cold.

 

[karlos1983]

Even by +288 things are looking interesting 

 

[Banbury]

6 minutes ago, karlos1983 said:

Even by +288 things are looking interesting 

 

Yep, going through the ENS there are some good one's that's for sure

[Derecho]

P11 plonks a ~1060mb high to the north of the UK

 

Though plenty others develop strong northern blocking and a few building pressure over Scandi next week so as has been said, perhaps the effects of the SSW starting to filter into the model output.

[Cloud 10]

Pretty solid looking ens. mean charts at 360 hrs from the o6z.

 

[Frosty.]

Late Feb looked Meh on the Gfs 00z op but this from the 6z is far more in line with the background signals..fingers crossed we see a sting in the tail to winter 2017 / 18 with wintry weather continuing well into march!!

[tight isobar]

3 hours ago, tight isobar said:

Looking like the point of change.

Taking gfs 'random- @180.

Anyone understansing the mechanics of modeling, will note that with n-hem signals (ssw-mjo phasing)..will have miss manage-b4 begining of decipher -align...

But we look 2 be at this stage of transfer and trop/strat developments are coming into range...

Expect to see big changes in these regions (snapshots)now in very near modeling...

And quite notable ones @that!!!.

As th pv comes under immense pressure .

With a rapid change in northern hemispheric synoptics.

10hpa(strat)..180hrs.

 

3 hours ago, tight isobar said:

Looking like the point of change.

Taking gfs 'random- @180.

Anyone understansing the mechanics of modeling, will note that with n-hem signals (ssw-mjo phasing)..will have miss manage-b4 begining of decipher -align...

But we look 2 be at this stage of transfer and trop/strat developments are coming into range...

Expect to see big changes in these regions (snapshots)now in very near modeling...

And quite notable ones @that!!!.

As th pv comes under immense pressure .

With a rapid change in northern hemispheric synoptics.

10hpa(strat)..180hrs.

Already more attractive ens..

London 6z gfs.

[stodge]

Afternoon all

Another day, another chilly but sunny one here in London. Plenty of talk regarding the impact of the upcoming vortex split and the tropospheric response but a lot of weather to come in the medium term which this morning means Friday February 16th as T+240:

Starting as always with the ECM 00Z:

Continuing from yesterday, the deep LP near Iceland is slowly filling and moving even more slowly east with a large HP ridge from the two HP cells over Azores and western Russia across central and southern Europe so there isn't anywhere for the LP to go at this time. The British Isles is in a cool unstable airflow with showers or rain likely further north (snow to hills) and the likelihood of secondary features and troughs augmenting the rain at times further south.

On then to GEM 00Z OP at the same time:

Some differences. The Azores HP more prominent and a ridge on the way but for now a cool WNW'ly flow with showers for many.

GFS 00Z OP at the same time:

With the trough positively aligned, warmer air over the British Isles with a WSW'ly airflow. The :LP is well back over SE Greenland with a pronounced ridge from the Azores into northern France. Decent conditions in the south but windier and more unsettled further north. Further into FI and pressure continues to rise from the south leaving the British Isles in a col between LP to the NW and SE and HP to the NE and SW.

GFS 06Z OP at T+234:

Between a very deep LP over the southern tip of Greenland and HP over Europe a mild SW'ly airflow affects the British isles. Dry in the south and east but more unsettled with rain and drizzle to the north and west. Further into FI and perhaps the effects of the stratospheric shenanigans begin to manifest as the Atlantic stops to a halt and pressure rises strongly over Greenland leaving the British Isles in an increasingly cold ENE'ly flow spreading from Scandinavia.

GFS 06Z Control at T+240:

Not too far removed from the OP - mild or very mild conditions across the British Isles with the south and east drier than the north and west. Into FI and the Control opens the door to an early spring with pressure rising to the south and east. Not what cold fans would want but a perfectly possible evolution.

The GEFS from 06Z at T+240:

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=240

A mixed bag but only a minority showing an immediate tropospheric response. A number have LP disrupting close to or over the British Isles but clearly the medium term evolution remains far from clear. Once again plenty of eye candy starting at T+312 and points onwards but certainly a larger minority of members slower to kill off the Atlantic than yesterday. Worth noting others set up HP close to or over the British Isles but the OP evolution certainly not without support.

In summary, little change from yesterday. Next week looks set to be Atlantic dominated and could get quite mild by the end of the week if GFS has it right. However, plenty of options for a windy spell of cool or cold zonality with rain or showers for many. Little immediate sign of trough disruption to the south but the very strong signal for a break in the Atlantic remains but whether that provides the coldies (and snowies) with what they want is far from clear at this time.

 

 

[Sky Full]

GFS 06Z keeps us mainly under colder uppers through to the end of the run and then tries to build a block towards Greenland, bringing even colder air back towards tthe UK.....

    

Is this the beginning of something worth watching, as predicted by some of the really knowledgeable posters on here?  I realise its way beyond the reliable timescale but there also signs in other long range models (CFS for one) that late February and early March will see Winter going out with a bang this year.  It looks like a colder than average February anyway, and possibly less rainfall than usual

EDIT:   OOps - this seems to contradict the immediately preceding post from my much more knowledgeable mate, Stodge!  If I am misunderstanding these charts I apologise for any misleading info posted....   Ignore me until I have been back and learned some more....

Edited February 6, 2018 by Sky Full
.

[Matthew.]

4 minutes ago, Sky Full said:

GFS 06Z keeps us mainly under colder uppers through to the end of the run and then tries to build a block towards Greenland, bringing even colder air back towards tthe UK.....

    

Is this the beginning of something worth watching, as predicted by some of the really knowledgeable posters on here?  I realise its way beyond the reliable timescale but there also signs in other long range models (CFS for one) that late February and early March will see Winter going out with a bang this year.  It looks like a colder than average February anyway, and possibly less rainfall than usual

 

Just shows the power of the Ssw doesn’t it. It throws the Atlantic to the side like paper. Remarkable-thanks

[Frosty.]

7 minutes ago, Sky Full said:

and possibly less rainfall than usual

 

less rainfall and more snowfall will suit me, not really seeing much in the way of mild, indeed, I'm seeing plenty of below average temps / cold weather still to come this month!❄❄❄❄❄❄❄❄❄❄

Edited February 6, 2018 by Frosty.

[Catacol]

12 minutes ago, Sky Full said:

GFS 06Z keeps us mainly under colder uppers through to the end of the run and then tries to build a block towards Greenland, bringing even colder air back towards tthe UK.....

    

Is this the beginning of something worth watching, as predicted by some of the really knowledgeable posters on here?  I realise its way beyond the reliable timescale but there also signs in other long range models (CFS for one) that late February and early March will see Winter going out with a bang this year.  It looks like a colder than average February anyway, and possibly less rainfall than usual

 

In a word - yes. It is exactly the response as some are seeing it, and for once it is a FI pattern that matches the double indications of pacific forcing and stratospheric warming following vortex split. There is currently a developing sense of inevitability regarding the pattern that is set to develop. That's a little worrying... cos Mother Nature rather enjoys making fools of forecasters. However setting aside that queasy feeling it seems likely that more and more of these reverse flow charts will appear, perhaps with variations on exactly where the block will setup.

The key is seeing them appear at t+72. Only then can relaxation come... though cold on its own is no guarantee of snow. And I hope the atlantic wont be completely brought to a halt because without approaching frontal systems the battleground will be empty!

[Daniel*]

1 hour ago, Cloud 10 said:

Pretty solid looking ens. mean charts at 360 hrs from the o6z.

 

Exceptional mean and highly likely general area of blocking as a result of SSW -AO is going to tank! 

[Nick F]

GEFS H500 mean/anomaly certainly suggesting its perhaps going through the motions of a tropospheric response to the SSW as we head towards late month, hopefully this is signs of a quick response to downwelling. The trop vortex over Greenland over next 8-9 days looks to shift into northern Canada day 10 onwards, perhaps due to the strat-trop coupling response to the  split over Greenland area forecast by the models. As a result, this opens up for height rises over Greenland, GIN corridor, Svalbard across to Russian arctic sea as below

A look at the  GFS zonal wind cross section shows the SSW occurring around the 12-13th Feb, then a reasonably quick downwellng of the wind reversal from zonal winds throughout the trop and strat currently, so no wonder the GEFS will picking up on this in mean heights later in the month.

  <---- click on image  to run the loop

EC from yesterday on Berlin sight shows downwelling by day 10 too.

  <---- click on image  to run the loop

 

Still uncertainty this far off over how quickly the trop responds to the downwelling - which will depend on how the PV splits which will determine where the trop responds first, so we won't know exactly which areas of the northern hemisphere will be impacted with regards to a upper flow pattern change for now.

Certainly plenty to be optimistic about but no guarantees, but based on previous SSW in February, no reason to think the intense PV over Greenland will be driving the weather for the rest of this month. Certainly the PV to our NW looks unlikely to extend its influence further east across Scandi / NE Europe, as a large upper block looks to hold sway over the coming 10 days or so, so the deep cold should be preserved should we tap into later this month as high latitude blocking perhaps develops in response to the downwelling of the SSW.

Edited February 6, 2018 by Nick F

[Stormeh]

Looking very interesting....

As people have already said, the models are already hinting at something special as we head towards the end of February. The winter of 2017/18 could possibly go out with a memorable cold and snowy spell of weather but this is the UK after all so nothing is certain but It will definitely be an interesting period of model watching over the next few weeks! 

[Catacol]

2 hours ago, Snowy Hibbo said:

Just following on from Tamara's great post above.....

Frictional Torque is currently going into a negative trend. After a FT peak, then followed the current MT peak, that has sent the AAM to it's current position. Below is my thoughts, based on my observations and forecasts of the key drivers. The FT will continue to decline into the negatives, and bring the AAM into a negative trend, towards a GWO Phase 7 & 8. But the question is will the MT make a full decline as well? Yes, you could try and use NWP to try and work out whether the EAMT will take a dive, or what will the Rockies MT do? These are the questions that need to be asked.

I am referring to the massive +EAMT, and the currently -RMT. Despite the sudden MT dive in the Rockies, the EAMT has been driving the Worldwide MT to levels that are quite literally off the charts. It is this, that has caused this AAM progression, that nobody forecasted and seems to defy the Niña base state. Whether this is an indicator of Niña weakening, or just a minor hiccup, isn't my question to answer, but many experts have been questioning the dominance of a Niña base state.

Anyway, this is my 'forecast'(yellow line), with annotations included. This assumes that the MT has a large negative trend, maybe it doesn't, and acts like a Niño GWO cycle. But I personally doubt this will happen, IMO that shouldn't happen so suddenly. It's one thing to have a +AAM, and another to have a Niño like GWO cycle. Anyway interesting times ahead, let's keep watch for the next steps of the AAM's progression.

All true. However I wonder whether conditions are about to change so that the pacific, for a while, has to take second spot and allow stratospheric developments to take the throne. I can feel a perfect A level-style history question emerging - "Assess the varying significance of factors that drive the tropospheric circulation in the North Atlantic"... with an answer that says: "At most times equatorial pacific energy is the prime driver of pattern development in the northern hemisphere" - but goes on to argue - "however, at times of high stratospheric vortex stress the tropospheric pattern, normally a product of upstream pacific forcing, becomes highly impacted by splits, stretches and sometimes reversals of stratospheric winds. This can create blocked pressure patterns regardless of pacific conditions."

All rather academic perhaps at the moment - both drivers are in unison about developments on the horizon. Interesting to mull over relative importance though.

As a question - how many SSW events have occurred at times of Nina dominance via low GWO orbit and an MJO passing through phases 1 - 4. Anyone got any data on that?

[Frosty.]

Just had a look at the Ecm 00z ensemble mean, nothing I would call mild but plenty i would call cold zonal, cold enough for snow at times with frosty, icy nights with the jet tilted nw / se  or at worst wnw / ese!

[Singularity]

Finally found a moment to check up on how the GFS 06z unfolded and I'm glad to see it tried for exactly the blocking sequence I picked out earlier as our best/only real chance of scoring big-time (albeit that was south-biased, I must admit!).

So... starting next week from the UK's perspective of the Atlantic troughs:

Attempt # 1 - Fail

Attempt #2 - Fail (but closer than the 00z GFS - broadly similar to ECM 00z)

Attempt #3 - Now we're getting somewhere! ECM 00z could well have gone in a similar direction although I do find the mess to the N and NE to be unconvincing.

Attempt #4 - Does not occur as far as the UK is concerned, as the HLB response has taken over proceedings. Left with the sense that it could have got to this stage a few days earlier.

[bluearmy]

54 minutes ago, Singularity said:

Finally found a moment to check up on how the GFS 06z unfolded and I'm glad to see it tried for exactly the blocking sequence I picked out earlier as our best/only real chance of scoring big-time (albeit that was south-biased, I must admit!).

So... starting next week from the UK's perspective of the Atlantic troughs:

Attempt # 1 - Fail

Attempt #2 - Fail (but closer than the 00z GFS - broadly similar to ECM 00z)

Attempt #3 - Now we're getting somewhere! ECM 00z could well have gone in a similar direction although I do find the mess to the N and NE to be unconvincing.

Attempt #4 - Does not occur as far as the UK is concerned, as the HLB response has taken over proceedings. Left with the sense that it could have got to this stage a few days earlier.

I think the hemispheric response to the ssw took over the week 2 evolution ...... 

 

Edited February 6, 2018 by bluearmy

[Kieran]

GFS 12z rolling out and is still showing rain turning back to snow on Friday morning across most of England.

It has been consistently showing this run after run. Is there a chance of this happening or is it another case of the GFS precipitation charts being all over the place?

 

[karlos1983]

9 minutes ago, Kieran said:

GFS 12z rolling out and is still showing rain turning back to snow on Friday morning across most of England.

It has been consistently showing this run after run. Is there a chance of this happening or is it another case of the GFS precipitation charts being all over the place?

 

Hi res paints a rather different picture 

And this is probably over playing the back edge I would imagine. 

 

Edited February 6, 2018 by karlos1983

[Daniel*]

27 minutes ago, karlos1983 said:

Hi res paints a rather different picture 

And this is probably over playing the back edge I would imagine. 

 

T+69 based on parameters modelled there very much could be back edge snow, dew points are well below freezing that is surprising. I reckon GFS has them too cold but interesting wave feature...

 

[Singularity]

So long ridging through Europe - GFS adjusting toward ECM.

Hopefully it will demonstrate even better than the 06z where the 00z ECM could have gone. It is GFS though so not holding my breath .

[Daniel*]

1 minute ago, Singularity said:

So long ridging through Europe - GFS adjusting toward ECM.

Hopefully it will demonstrate even better than the 06z where the 00z ECM could have gone. It is GFS though so not holding my breath .

ECM 00z op was a huge outlier in FI. 

[Daniel*]

No surprise there AO is forecast to sink like the Titanic. Could be even more spectacular with prominent positive AO beforehand.

Edited February 6, 2018 by Daniel*