Model output discussion - The run up to Christmas

[IanT]

31 minutes ago, Scott Ingham said:

Theres nothing concrete yet in Icelandic heights. Eps wants nothing to do with it but when looking at suggested momentum dates and factoring in timings for EAMT events i called Gricelandic heights a week ago.

With wavelengths slowly changing with each push of amplification coupled with ensembles support for a move west of the Russian high logic dictated this as a possibility.

Its still a small possibility atm but long range forecasting of AAM which is more my speciality did put this pattern firmly in thoughts. 

Its nice to test your own theories and see them being forecast and if it doesnt come off its an opportunity to exam why and go again.

Again all very fascinating. What an interesting brilliant start to 2020 winter

Well it’s frequently brilliant at T+10 in the models. Not yet on the ground at T0.

[Scott Ingham]

Just now, IanT said:

Well it’s frequently brilliant at T+10 in the models. Not yet on the ground at T0.

Patience grasshopper its coming

[northwestsnow]

The pattern looks good....Being honest I would like a nudge east of the troughing dropping south .

Normally I would expect a nudge east, but the Russian high is being modelled to push west ,in this instance seemingly preventing this eastward shift..

As it stands I'm not expecting snow on my location, but 300m plus should be enough ...

Fingers crossed ...

Edited December 22, 2020 by northwestsnow

[Kasim Awan]

Euro4 churning up precipitation associated with the trough. Possibility for temporary lowering of the snowline with this - North York moors producing some orographic lift too.

[Mike Poole]

21 minutes ago, Scott Ingham said:

You only have to private message me if there is anything you dont understand mate in that regard. I have enough knowledge when it comes to the strat. Not enough to make a forecast based on it however. You probably know more than me on this subject. Im probably wrong but im own theory looking at the last split is if that came to pass (and the positions on the splits if we even get a split at all are going to change down to T-0) is that that surely would only reinforce a pattern seen at the end of the 18z which would see it only get colder and colder?

Thanks mate, may well do so in quieter times!,  re the strat, I think a split like on the 12z:

Would indeed lead to a locked in cold pattern for several weeks for the UK.  Trouble is 18z is much messier:

I think it is best to view these as individual members of a larger ensemble, and probabilistically we can say a favourable split is on the cards, more runs seem to be going with it than not.  Would like to see it come into the range of the ECM on the Berlin site before being certain though.  

Meanwhile, GEFS mean  T240 still showing more promising than the ECM EPS, notably trough in S Europe:

 

Edited December 22, 2020 by Mike Poole

[Kasim Awan]

2 minutes ago, northwestsnow said:

The pattern looks good....Being honest I would like a nudge east of the troughing dropping south .

Normally I would expect a nudge east, but the Russian high is being modelled to push west ,in this instance seemingly preventing this eastward shift..

As or stands I'm not expecting snow on my location, but 300m plus should be enough ...

Fingers crossed ...

300m plus will be the day time non evap cooling snow line I think.. 

[damianslaw]

Not had much time today to comment on the charts.. alas all I can see is a generally cold outlook bar the blip on Boxing Day. Last time we could have said this on 22 Dec was in 2009, in 2010 there were signals of a milder outlook come the New Year.

Will have more time to comment on models and trends for the New Year tomorrow before a break over the 3 day Christmas period.

Edited December 22, 2020 by damianslaw

[Scott Ingham]

4 minutes ago, Mike Poole said:

Thanks mate, may well do so in quieter times!,  re the strat, I think a split like on the 12z:

Would indeed lead to a locked in cold pattern for several weeks for the UK.  Trouble is 18z is much messier:

I think it is best to view these as individual members of a larger ensemble, and probabilistically we can say a favourable split is on the cards, more runs seem to be going with it than not.  Would like to see it come into the range of the ECM on the Berlin site before being certain though.  

Meanwhile, GEFS mean  T240 still showing more promising than the ECM EPS, notably through in S Europe:

 

Yeah whenever you like mate. Im all for sharing knowledge its why im here to improve on areas im sure of.

@lorenzo has already been kind enough to send me some papers on the strat as an example.

Is it normal for charts at +384 to be inconsistent on a lead up to a ssw??

[Mike Poole]

8 minutes ago, Scott Ingham said:

Yeah whenever you like mate. Im all for sharing knowledge its why im here to improve on areas im sure of.

@lorenzo has already been kind enough to send me some papers on the strat as an example.

Is it normal for charts at +384 to be inconsistent on a lead up to a ssw??

I think if a warming is coming from 1 hPa down then the strat forecasts should be accurate from some way out.  But that’s not the case with this baby!  the vortex is under attack from all quarters and those coming from the troposphere would i imagine be subject to the usual level of uncertainty once you get beyond a week or so.

But my experience is once you see those splits on the GFS on most runs at T384, it will count down.  (based on personal experience of 2 split SSWs, I should add - these things don’t happen very often!)

Edit - just to add, we have the FV3 GFS now, some think it is better in the strat than the old version.

Edited December 23, 2020 by Mike Poole

[MATTWOLVES 3]

Things ticking a long nicely,and a few nice ens to boot... And a  big shout out to me Dog jess for working overtime with these GFS updates.. Steak dinner for you this Xmas mate..

[Scott Ingham]

4 minutes ago, Mike Poole said:

I think if a warming is coming from 1 hPa down then the strat forecasts should be accurate from some way out.  But that’s not the case with this baby!  the vortex is under attack from all quarters and those coming from the troposphere would i imagine be subject to the usual level of uncertainty once you get beyond a week or so.

But my experience is once you see those splits on the GFS on most runs at T384, it will count down.  (based on personal experience of 2 split SSWs, I should add - these things don’t happen very often!)

Edit - just to add, we have the FV3 GFS now, some think it is better in the strat than the old version.

Would it not be a worry they arent counting down then? Ive seen about half of the op runs throw one out at 384 and half not 

[kold weather]

The 18z suite of ensembles does look a little warmer at 850hpa after the initial LP on the 27-29th...but as per Snowking earlier, that is masking what is actually happening.

That is we seem to rotate in LP's towards our general area. It prevents the uppers getting quite as cold but with a decent undercut from Europe looking very possible if we can get the right angle, it won't really matter much providing we don't see any meaningfully deep depressions to our SW.

In the later parts of the runs the ensembles move more towards a high pressure being a little further SE than previous runs, however it is but one suite and means little on its own.

Before that and I'm still moderately confident we could see a fairly decent spell of snow between the 28-29th, though details probably won't firm up this side of Xmas on the chances.

[Mike Poole]

2 minutes ago, Scott Ingham said:

Would it not be a worry they arent counting down then? Ive seen about half of the op runs throw one out at 384 and half not 

I think I’d say give it time, it is complicated this time because it is i think is trop led, and that may lead to the models being less certain, and it is 3-dimensional anyway, I’m sure it is going to blow (by which i mean reversal at 10 hPa 60N), but in the meantime, here’s the NAM plot, negative all over (GFS forecast):

[Scott Ingham]

4 minutes ago, Mike Poole said:

I think I’d say give it time, it is complicated this time because it is i think is trop led, and that may lead to the models being less certain, and it is 3-dimensional anyway, I’m sure it is going to blow (by which i mean reversal at 10 hPa 60N), but in the meantime, here’s the NAM plot, negative all over (GFS forecast):

That is some NAM plot

[georgiedre]

Seen this on twitter would this mean a cold outcome for the UK?

[tight isobar]

2 minutes ago, georgiedre said:

Seen this on twitter would this mean a cold outcome for the UK?

Doesn’t get any better than those plots... and short answer @YES... with bells on it

[SLEETY]

7 minutes ago, georgiedre said:

Seen this on twitter would this mean a cold outcome for the UK?

Yes indeed, the Siberian High could well be making a visit soon, then no more worry about uppers, lol. 

The lower the uppers a good chance of lake effect snow as the winds move over the warm north sea and pick up moisture and dump it as snow on the coast like in Japan recentlywith over 7ft of level snow.Same here? Don't rule it out. 

Even the mild ramping BBC forecasters are talking about snow from next week's onwards, virtually anywhere! 

Edited December 23, 2020 by SLEETY

[Cheshire Freeze]

33 minutes ago, georgiedre said:

Seen this on twitter would this mean a cold outcome for the UK?

Essentially saying that if that outcome is realised, Europe could see a severe Siberian blast or 'Beast from the east'

Given the coldest upper air is sat over that side of the hemisphere, if that was to hit in mid- late January then it could produce some severe winter weather for Europe.

[kumquat]

Don't have time to go back through last 5 pages but I think the 18z pulled it off. All cold air aloft in our vicinity finds the sharpest route earlier on.

Iceland High right out at 384 (sustained). Another low coming under the block.

Things might pause here. We need cold to the East but this pattern in itself has helped pull all cold towards our shores.

It's a bit worrying no cold is coming under the Siberian Block, but this is not a regular season.

 

Edited December 23, 2020 by kumquat

[Scott Ingham]

20 minutes ago, CreweCold said:

Essentially saying that if that outcome is realised, Europe could see a severe Siberian blast or 'Beast from the east'

Given the coldest upper air is sat over that side of the hemisphere, if that was to hit in mid- late January then it could produce some severe winter weather for Europe.

2018 - Coldest upper air sat over Russia after the split - Blocking settled over Scandinavia

2020 - Coldest upper air sat over Scandinavia - Blocking stretched between Greenland and Iceland

Unfathomable the range of scenarios and severity of cold given how much closer to that piece of vortex well be.

A more sustained 1987 North Easterly.

Oscillating Northerlies/North Easterlies/Easterlies.

Cold entrenched and southerly tracking lows.

It probably wont happen like this but in theory it could do with a lot of luck

[kumquat]

34 minutes ago, CreweCold said:

Essentially saying that if that outcome is realised, Europe could see a severe Siberian blast or 'Beast from the east'

Given the coldest upper air is sat over that side of the hemisphere, if that was to hit in mid- late January then it could produce some severe winter weather for Europe.

Agreed, but it will take a time to come around. 18Z GFS seems to offer the fastest route to cold (almost possible) in the short term, but getting really cold here seems a circuitous route that will take time. (Mid Jan seems a good shout)

[tight isobar]

Gfs 00z sets the wheels firmly in motion... 80%ppn all snow .. and in heavier geographic... again.. I cannot mention-emphasise enuff.. that the crucial 850s are still ripe.. for fruition.. and will highly likely decrease (perhaps significantly)-as we gain... ya want winter.. you’ve got winter... on we roll

[Mr snowman 2018]

Gfs +150 is a thing of beauty

[SMU]

Improving !!

[tight isobar]

Some chart this @156.. has distruption written all over it @central/-southern England!!!!!!