The hunt for cold - Model discussion (late November)

[Guest]

31 minutes ago, Tim Bland said:

ECM Is definitely the pick of the bunch today! Here is the snow fall by next Friday from ECM 

 

oh me oh my i seem to be in that dark purple bit in Scotland. some cracking charts this morning and just for fun at this range.

[Paul]

9 minutes ago, More Snow said:

oh me oh my i seem to be in that dark purple bit in Scotland. some cracking charts this morning and just for fun at this range.

Be ultra-careful with those charts, they really overdo the snow..

[Met4Cast]

ECM Op is such a tease..

Not sure why everyone is downbeat, I read the forum before looking at the models and was assuming everything had on pear shaped, all looks fine where I'm sitting. Not too concerned with the 850hPa temps at this juncture, how many times have we seen them be upgraded as the time period closes in?

EPS seems to show the first Atlantic attack undercutting, the second attack makes more inroads into the UK days 10 and 11, extended out to day 15 shows low pressure over the UK with Scandi blocking subsiding, though it's a little too early into proceedings to buy into that just yet..

[Catacol]

7 hours ago, CreweCold said:

I hear that SSWs can 'knock us out' of a cold spell. However, I think what has to be understood is that this is most likely when we already have Greenland blocking running the show. SSWs basically set the (upper) zonal flow into reverse which means that if Greenland blocking has already taken hold, a west based set up becomes more likely (the high retrogresses even further). 

 

Yep - I'm never one to be pessimistic when it comes to seeing cold on the horizon....but it is worth pointing out that a really really special spell of weather in March was turned into a special one only, precisely because the extreme nature of the reversal had a feed from Siberia to Canada the wrong way, and it moved the block so far west so quickly that we got an unexpected warm undercut from Portugal that rather spoiled the epic party. It created some unbelievable scenes here in the SW where we had an inch of frozen rain sitting on top of 5 inches of snow....and houses were caked in the same frozen rain - but it brought that spell to an end around a week earlier than was expected.

So we do have to be a bit careful when looking and predicting the impact of an extreme type vortex shredding event (assuming it arrives in the first place....) I think CreweCold referred to it in the strat thread as "buying a ticket" - we have certainly got a ticket here.....but we cannot be sure exactly what the show is going to be. Ideally we want blocking to the NE and NW to oscillate in between Greeny and Scandy under conditiions driven by the high impact tropical wave present at the moment and the impact of reduced westerlies and even possibly a reversal up above. But these are fine margins. A bit too much to east or west on that oscillation and warm air will be sucked in occasionally/regulary....and the atlantic will not go completely quiet in winter. So dont expect wall to wall cold. Be realistic and accept that all weather types are still on the table and likely at stages over the next 3 months.

I'm clutching my ticket and hoping for the weather equivalent of Muse in Concert....

[Mike Poole]

Well 5/21 of the GEFS showing a technical SSW this morning, 6 if you count the one that just hits the line...the signal grows stronger.

[Catacol]

And here comes the next MJO cycle - and again it looks strong. Bit of a head scratcher that - but if it maintains the amplitude of pacific forcing given other background conditions then bring it on....

Edited December 5, 2018 by Catacol

[Glacier Point]

Whilst the gist of the extended GEFS and EPS looks credible (+ve height anomalies centred Hudson Bay), there's any awful lot of white space across the rest of the Northern Hemisphere. Suspect that modelling remains too progressive w/r/t Scandinavian ridge demise, and, possibility that we will retain some weakish +ve heights to our north in the run up to Christmas.

My punt of technical strat warming date would be 26th December.

[Had Worse]

4 minutes ago, Daniel Smith said:

ECM Op is such a tease..

Not sure why everyone is downbeat, I read the forum before looking at the models and was assuming everything had on pear shaped, all looks fine where I'm sitting. Not too concerned with the 850hPa temps at this juncture, how many times have we seen them be upgraded as the time period closes in?

EPS seems to show the first Atlantic attack undercutting, the second attack makes more inroads into the UK days 10 and 11, extended out to day 15 shows low pressure over the UK with Scandi blocking subsiding, though it's a little too early into proceedings to buy into that just yet..

I compare the charts to aiming at a target. Your sites start at the edge, meander towards the middle (which maybe the point where the eye candy shows on several charts), you go past the centre (sweet spot) and then meander again pulling the trigger. The point being, the charts can all show the perfect synoptics now or close to across several models for 5 days away then drift away from the sweetspot. Its also perfectly possible that on the second pass, they come back to the sweetspot, which I would call an upgrade. 

Nothing to worry about, we have 3 months of winter and March is the bonus ball .

[Tim Bland]

15 minutes ago, Paul said:

Be ultra-careful with those charts, they really overdo the snow..

Been discussed a few times and most agree that the algorithms for ‘falling snow’ are correct. But It over estimates the ‘accumulating snow.’ Hence why I chopped the bottom off the image (showing depth) before posting 

[MR EXTREMES]

11 hours ago, Singularity said:

Overall, extended modelling seems a little progressive on the shift west of the main high-latitude blocking focus; west-based negative NAO setup arriving a bit soon with too little of an east-based negative NAO interlude beforehand.

As and when we do see the west-based negative NAO it'll be hard to hang onto cold conditions but not out of the question should we see enough of a displacement of the stratospheric vortex toward Siberia; that could feasibly allow blocking to reach further east than usual for a situation where the blocking is focused over the NE of N. America.

Not worth getting too involved with at this time of course; let's hope we can first get a good bout of cold air in during the middle of the month.

and following on from this yesterday.

todays charts certainly show your ideas well.

i think the other problem is lack of lower heights to our south we need the heights around the azores to surge north or north east like 09/10 winter.

it undoubtedly very knife edge any correction west would help but im back on the fence.

but gfs still adding wave attack on the vortex id of thought if we can get through this month with continued disruption to the vortex, then we might bypass the peak cooling leaving the vortex more vulnerable.  

northern arm of the jet stream or the split part of the jet stream is interesting to, as momentum  is weaker on the northern part of the jet as it loops around but the usual track of the jet is not raging like previous years.

and the qbo needs to be kept an eye on because a strong westerly qbo might just put the breaks on a knife edge winter.

but this year there are lots pluses for this winter.

but this mornings runs are ok but not really holding steady very fluid flow at the moment.

[weirpig]

10 minutes ago, Glacier Point said:

Whilst the gist of the extended GEFS and EPS looks credible (+ve height anomalies centred Hudson Bay), there's any awful lot of white space across the rest of the Northern Hemisphere. Suspect that modelling remains too progressive w/r/t Scandinavian ridge demise, and, possibility that we will retain some weakish +ve heights to our north in the run up to Christmas.

My punt of technical strat warming date would be 26th December.

So by that  i expect a 3 weeks lag time  which would make the possible effects felt in the middle of January.?  perfect timing right in the depths of winter. 

[carinthian]

18 hours ago, carinthian said:

Had an interesting chat with the forecast team earlier. Basically the same and that is for high pressure to be NE of the British Isles during period 192-240T and formation of upper low over the continent to possibly move westwards towards Souther Britain. They think this 2nd attempt of cold from the east will be a bit more robust than the first one a few weeks ago but expect it to be repelled again for a few days. However, their longer term charts now indicate a 3rd and more potent attempt to bring cold down from the Arctic the week before Christmas. Now that's exciting . Third time lucky , but colder scenario is the theme for the outlook.

C

Morning all, ECM run certainly pick of the models regarding our hunt for cold. Remember in the post above sent this time yesterday , I did mention formation of a Upper Low showing over the continent .It looks like ECM has also picked this up as well and likely to move towards the Southern part of the British Isles with an associated area of lower 850 mb height temps. So snow starts to come into the equation for your part of the world from the period 168T. Its still along way off but our outer perimeter snow forecasting model may soon pick this up. Will talk to the experts later this morning with their updated single model run to see if the this threat is still an on going feature.

c

Edited December 5, 2018 by carinthian

[Catacol]

24 minutes ago, Glacier Point said:

Whilst the gist of the extended GEFS and EPS looks credible (+ve height anomalies centred Hudson Bay), there's any awful lot of white space across the rest of the Northern Hemisphere. Suspect that modelling remains too progressive w/r/t Scandinavian ridge demise, and, possibility that we will retain some weakish +ve heights to our north in the run up to Christmas.

My punt of technical strat warming date would be 26th December.

Ah Stewart - I can almost taste your desire to reveal your Jan/Feb thoughts. Not seen you post this often in years. I'm not sure we could pick a better date for the start of a warming event than last week December given potential lag impacts over the following 60 days. The question is - will wave 2 warming shred it completely, or do we get a much weakened but displaced vortex under primarily wave 1 forcing?

50hpa vortex very stretched at the end of next week on the Attard plots

 

Could do with a killer Wave 2 punch at this point. Current forecast perhaps not quite sufficient for that?

Next MT cycle and pacific jet extension peaking circa 15 Dec perhaps to deliver this around 10 days later - hence 26 Dec?

Edited December 5, 2018 by Catacol

[Man With Beard]

GFS Parallel 00Z (sorry a bit late on this!): this time it contrives to spoil the pattern soon after this point, but I'm guessing battleground snow may be possible as the incoming front moves in from the SW:

  

Given everything I've seen this morning and yesterday, I think a big snow-event for some towards the end of next week is approaching the 50/50 mark.

 

[Weegaz]

Before the cold we have this feature passing through, hopefully the last for a good while, it’s potency has changed quite a bit on the last few model runs, MO yellow warning in place since yesterday

[weirpig]

Just now, Weegaz said:

Before the cold we have this feature passing through, hopefully the last for a good while, it’s potency has changed quite a bit on the last few model runs, MO yellow warning in place since yesterday

Yes Weegaz  i noticed this. It also seems to have deepened slightly since the 0z run  Scotland and the borders could get rather wild into Friday 

[Methuselah]

And here comes the Thundersnow ball!

[Weegaz]

2 minutes ago, weirpig said:

Yes Weegaz  i noticed this. It also seems to have deepened slightly since the 0z run  Scotland and the borders could get rather wild into Friday 

Looked deep on Monday then yesterday looked to be fizzling out, picking up potency again

[Iceaxecrampon]

15/12/18

Cold getting in place from the East

.......and "Bump"for Wales?

Potential has been there for mid December the last few runs.

[shaky]

Any upgrades or downgrades on gfs 06z!!

[swfc]

Hmmm 6z gfs looking a bit light weight with the ridge wanting to go to scan?? Atlantic just looking imo a bit more east

Edited December 5, 2018 by swfc

[Weathizard]

Markedly weaker ridge on this run but actually could help us out as pressure has risen around Greenland compared to the 0z

[MR EXTREMES]

 

looks like heights are getting the squeeze is going to be able to inject any heights further north or northeast thats the problem.

might take couple of attempts. 

 

[MR EXTREMES]

1 minute ago, MR EXTREMES said:

 

looks like heights are getting the squeeze is going to be able to inject any heights further north or northeast thats the problem.

might take couple of attempts. 

 

looks like the lower heights are forming to our south extra support for the northern blocking.

but most likely still going to ditch the whole lot by the end of the run.

but hopefully not.

[Jonathan Rhodri Roberts]

1 hour ago, Tim Bland said:

ECM Is definitely the pick of the bunch today! Here is the snow fall by next Friday from ECM 

 

A classic easterly set up there, with many of us in western areas (away from the north) staying dry, probably much more sunnier too with frosty nights throughout that time period