Model Output Discussion - Into the new year

[Stu_London]

2 minutes ago, Paul_1978 said:

I'm getting visions of Feb 1991 here (rightly or wrongly), and the famous Ian McCaskill forecast where he talked about the low pushing up from France. It was such an epic event having those bitter Easterly winds, but those aren't necessarily any good without come kind of weather system nearby - which is why I often look for low pressures lurking when there's an easterly around, especially to the south and moving north, to give us copious snowfall. Lots of interest in the models tonight and no doubt the coming days. Bring it on!

Apart from the -5 daytime temps, -16C uppers and 1050mb Scandi High, I would say it is pretty much an exact match

[Kasim Awan]

FMI Hirlam shows potential for south eastern parts late tomorrow.

Higher parts of Yorkshire getting pummelled by the streamer atm.

[Osbourne One-Nil]

You're watching "The Model Discussion Thread"....just to clarify!

[iceman1991]

Great news guys from the other side of the pond from  weather outlook Brian posted this on the forum glad he’s on board now as I highly rate him 

 

Brian Gaze    

Posted : 27 December 2020 19:07:52(UTC)

Best set of runs for cold weather since 2018 IMO.  Someone on Twitter mentioned Jan 19 but that always looked flaky to me despite the forecasts coming out of Exeter at the time. This now looks relatively solid.

[Stu_London]

Just now, Gadje said:

Had we the internet back then I'll bet some would have said it wouldn't happen.

I think the first most knew about it was about 3-4 days before on the Sunday countryfile forecast when John Kettley flagged up the coldest spell of weather for around 4 years (presumably referencing Jan 1987). 

Computerised models were around then but not in the public domain. Met office and sensible media (i.e not the Daily Express) haven't changed their habits much in 30 years - still like to sit on the fence until around 3-5 days from any event, which says a lot about where FI starts. 

[APerez]

Great to see the mood in here so jovial this evening, and for good reason of course  Looking at the shorter term we have a snow risk for the western half of England as well as Wales going into Monday morning as an occluded front swings south...

Further interest later in the day as the low circulates eastwards. On the northern side of the circulation we have interest coming in off the North Sea as precipitation moves inland. Potential for a spell of snow to affect the Wash and the E Midlands. One expects further changes and a 'nowcast' situation as these disturbances continue to challenge the hi-res models...

Further disturbances will likely appear within the 24-36hr timeframe as we head through next week. You can see just how busy the t+36hr FAX chart is this evening...

I'm sure most of us are wary enough not to trust precipitation models at mid to long range, as well as being healthily sceptical of short-range output, especially when marginal wintry situations present themselves. If anything that makes the coming days that more fraught with excitement as I'm sure some surprises will await ( for balance: as well as crushing disappointments  ).

Heading towards the end of next week, we have lovely consistency at t+120 with a slack flow from the north-northwest and strong WAA in the mid-Atlantic which later forms high pressure to the north or north-east...

ECM:  GFS:  GEM: 

You can see looking at the t+192 chart from the ECM the effect of that warm air advection with a lovely profile to the north...

Without wanting to go chart crazy, I will note that the GFS and GEM play on a similar theme and it seems all roads lead to a deepening of cold. Perhaps not as deep as one might hope for such a favourable time of year, but we have to accept that for what it is an appreciate the stunning synoptics we have at the moment. Should we see such prolonged cold then the uppers become less important as our landmass becomes ever colder anyway  Still, as I mentioned before, the pattern leads to deeper cold anyway as we see an easterly solution become the favourite by day 10...

ECM:   GFS: 

At this point we have lower pressure to the south which enables us to import colder air from the east, as seen on the ECM 850s below. The GFS is less settled at the same stage, bringing low pressure closer to our shores and the risk of a rain to snow event for many.

ECM 850s at Day 10: 

It is worth noting that even when the GFS trends less cold for a time at Day 10 it never actually becomes 'mild'. Instead we see the low pressure trundle eastwards allowing a renewed surge of cold air to plunge down from the north with signs thereafter of further amplification in the Atlantic... and this is at t+384  

I'll finish with a very enticing ensemble set from the GEFS 12z. We're in the infancy of this cold spell and many of us will no doubt have to be patient when it comes to snow. With such prolonged cold on the horizon though the chances surely increase with every frigid day that passes. It's been a long while since we've been able to witness such wonderful charts and these snow row figures for Sheffield below are the most impressive I've seen so far this winter (sorry, Sheffielders I've picked you because you can often do well in cold spells) (albeit the GFS snow rows are temperamental and prone to change) and should hopefully boost those who are in need of one at this early stage given the risk of snow is not yet a widespread one

Alex

Edited December 27, 2020 by APerez
formatting

[The Enforcer]

39 minutes ago, Tim Bland said:

Re Easterly at end of ECM - Hopefully the DP come the time will be lower as it’s still showing rain. I guess it will cool down with time, so only a couple of days of marginal conditions before the colder air sets in? 

This is the bottom line. However, how accurate are DP forecasts likely to be at T+192? I suspect the answer would include the words "very" and "not".

[MildCarlilse]

8 minutes ago, Stu_London said:

 

Fully expect this to get moved to the moaning thread but it isn't a moan, it is a realistic appraisal of the model output as I see it.

This thread is a great read and the models are positively eye candy compared to the last couple of years, however lets not forget.

• the best charts have always been and remain just out of the realistic time frame at +120 onwards.
• there remains anomalous warmth over much of Europe. Very few cold spells that only affect the far west of the continent are severe or have any sort of longevity. 
• the 850s are still an issue. Temps over much of the country will easily get above freezing on most days meaning any ppn will be marginal and if we do get any settling snow, it will likely rapidly thaw. 
• it has been a mild and wet December - there is latent heat in the soil meaning snow might not settle or will thaw from the ground up if it does settle. 

To my mind, a severe winter spells mean lying snow for several days and temps struggling to get above freezing. Whilst there are some encouraging building blocks in place for this to happen at some point, I would suggest to newbies reading the forum to enjoy the banter, but divide what is actually being predicted by about 10.

 

As I see things my friend,

.the best charts have always been and remain just out of the realistic time frame at +120 onwards.

Actually,the best charts are the synoptics right now.

.there remains anomalous warmth over much of Europe. Very few cold spells that only affect the far west of the continent are severe or have any sort of longevity.

Temperatures over large land masses drop quickly response to cold air.

.the 850s are still an issue. Temps over much of the country will easily get above freezing on most days meaning any ppn will be marginal and if we do get any settling snow, it will likely rapidly thaw.

A detail only.

.it has been a mild and wet December - there is latent heat in the soil meaning snow might not settle or will thaw from the ground up if it does settle.

Again,a detail only.  

.To my mind, a severe winter spells mean lying snow for several days and temps struggling to get above freezing. Whilst there are some encouraging building blocks in place for this to happen at some point, I would suggest to newbies reading the forum to enjoy the banter, but divide what is actually being predicted by about 10.

No one is predicting a 'severe winter',what the models are showing is a pattern conducive to sustainable cold weather here in the U.K.How things actually transpire in people's back yard is subject to variability but, the synoptics ARE conducive to and suggest very favourably that at least in the reliable timeframe which seems to be beyond 120hrs,things are cooling off. 

[Mike Poole]

So, the radar looks like this and the EURO 4 looks like this at same time, now:

Cumulative snow fall chart from same model out to T54:

Initial thoughts are that it is a good match but the actual system might spin a bit further east?

[Met4Cast]

1 minute ago, Mike Poole said:

So, the radar looks like this and the EURO 4 looks like this at same time, now:

Cumulative snow fall chart from same model out to T54:

Initial thoughts are that it is a good match but the actual system might spin a bit further east?

Seems further east than most models to me, particularly across Scotland, always difficult to tell where these bands are going to go though, the front is going to pivot slightly & models never accurately predict situations like that. Nowcast situation for sure!

Reports of heavy snow to low levels across NI coming in on Twitter now though, so that's encouraging for anyone else in the potential firing line.

[sheikhy]

2 minutes ago, Mike Poole said:

So, the radar looks like this and the EURO 4 looks like this at same time, now:

Cumulative snow fall chart from same model out to T54:

Initial thoughts are that it is a good match but the actual system might spin a bit further east?

Looks like its further east already and earlier!!

[BlueHedgehog074]

1 minute ago, Allseasons-si said:

Just catching up as i had to nip out but that day chart from the ECM is marvelous

 

That High Pressure over Northern UK is stretched like an elastic band!

Just a little look at the 12Z GFS, ECMWF and GEM, though, and they all have some kind of Easterly over the UK and Low Pressure to our South or South-East. High Pressure to our North:

GFS

 

ECMWF

GEM

As you would imagine at that frame, differences with the shape and placement of the High Latitude Blocking cells, and the Southerly tracking Lows. ECMWF furthest South with the Northern UK High over South-Eastern Iceland, but still far enough North to allow an Easterly to spill through the whole UK. GEM on the other hand is the furthest North with the Southern/South-Eastern UK surface Low Pressure and a South-West to North-East orientated curvy High to our North. There’s a flabby  Low over South-Western UK, which considering how slack it is along with the -5*C and slightly colder 850 hPa temperatures covering whole UK could provide some wintry weather for some in that area 

 

All mostly for fun at that time period. But good to see the 3 main operationals are going for the Easterly and High Latitude Blocking scenarios at that range. Just need it now to reach the 24 - 72 hour period. Easterlies can be that sneaky sometimes that it would be best to see ‘em get to 72 hours or under. Otherwise it could be going, going, gone!

Before getting to that though, this week is looking chilly. Low Pressure over the UK looking to transfer to our East, while at the same time the mid-Atlantic ridge becomes very amplified. GFS showing the ridge poking Northwards through Iceland by Friday this week with notable vertical development (see 4th chart below)
 

A chance of some white surprises for a number, especially frost, mist and/or fog, but some wintry showers and longer spells of rain, sleet and possibly snow, most especially over high ground, in the flabby North-Westerly to Northerly flow this week. Some places could stay dry at times, although some of the trough and disturbances in the flow could provide some surprises anywhere in the UK. Depending really how it all keeps developing. 

No doubt tomorrow could see a lot of windows being occupied regarding Western, Southern and perhaps South-Eastern UK rain, sleet and snow prospects. Maybe hopefully some in the Midlands too

[danm]

2 hours ago, Weathizard said:

When the wind direction is East 850’s don’t even need to be -5 to deliver widespread snowfall, in fact some of the biggest snow events in recorded history have been with uppers that are only just below freezing, air sourced from the east means it’s drier, lower dewpoints and less modification.

One correction I’d make to this - when we’re talking about convection, we need sufficient difference between sea surface temperatures and 850’s to spark off snow showers, otherwise it can be cold and dry. So with our typical North Sea temperatures in winter, you’d ideally want -6c to -7c 850’s or lower. However if we’re talking about a low pressure system bumping up against the colder airmass then higher 850’s are perfectly fine, especially if we have winds feeding off the continent. 

[Mike Poole]

ECM mean T240

I have never ever seen a chart like this?  I mean, where has the bottom half of it actually gone?

[Weathizard]

Beaut of an ECM mean at day 6, the ECM does appear to be making more of that ridge towards Iceland, the GFS cut off heights whereas the ECM builds stronger heights.

GFS op was keen on the Atlantic disrupting & undercutting driving troughing south of the U.K. with the jet deflected by the cut off wedge over Iceland.

 

[sheikhy]

The mean cold and easterly all the way till the end!!!

[Allseasons-Si]

The ECM mean is a corker...

starting to look like the recent EPS anomaly chart now(12z not out yet).

rotated it.

 

 

Edited December 27, 2020 by Allseasons-si

[Howie]

The mean makes much less of South east euro ridge, great

[The Enforcer]

9 minutes ago, Met4Cast said:

Seems further east than most models to me, particularly across Scotland, always difficult to tell where these bands are going to go though, the front is going to pivot slightly & models never accurately predict situations like that. Nowcast situation for sure!

Reports of heavy snow to low levels across NI coming in on Twitter now though, so that's encouraging for anyone else in the potential firing line.

The short-range models are highly likely to keep changing their forecasts for these areas of precipitation. I am expecting the 00z & 06z outputs to differ from the 12z and for each other.

[chionomaniac]

1 hour ago, Catacol said:

Everyone will be playing coy when considering this question....but a few pointers. Amy Butler a while back plumped for 9th Jan. Chio earlier today has said 10th. My first guess a while back of 23rd Jan looks way out. A warming is definitely going to happen - what is less clear is whether it will displace the vortex or split it in half..,.and associated with that whether we get a reversal of the flow.

Im always glass half full.....so let’s paint the best picture possible. Reversal kicks in 7th January (some runs have this so I’ll take this date as the starting point) and the vortex splits. As @snowking mentioned just now we get a vortex shard drop into Siberia and then rotate clockwise with the reversed flow. Greenland block strengthens and ridges across to Scandy because of the gap left by the split vortex. Siberian air undercuts. With such a blocked pattern already in situ thanks to favourable trop led forecasts and processes at the moment maybe downwell impacts within 7-10 days. This would mean a cold, maybe brutally cold, easterly pattern from mid Jan onwards. Duration uncertain. 

Lol. I’m daft enough to have thrown my hat into the ring a fortnight ago with the 10th. 

 

Nothing has changed my thoughts too. Will be very happy if it verifies as signals were suggesting later than this at the time.

[Weathizard]

Could this be an occasion where we actually want the GFS making more of that low at day 6 to be correct, with a stronger low that ends up cutting off the high and disrupting underneath, the ECM has a much more docile Atlantic and so the high is much stronger.

High risk for high reward, I prefer the GFS, FWIW I think the UKM looks more like the GFS 12z than the ECM

Edited December 27, 2020 by Weathizard

[MATTWOLVES 3]

The ECM mean goes with the Estly also...the mean stays solid,little change from the 0z..Things going nicely,but I'm expecting upgrades in the coming days. A rather satisfying day of model output im sure you would agree.

 

[bluearmy]

Sst’s between the Netherlands and e anglia are as high as we’ve seen since 2015 

that 2c above where we would expect to see them does make a difference to the easterly and Dp’s /air temps 

[Captain Shortwave]

ECM ens

 

 

pretty good support for the runs shown this afternoon. A developing easterly looks a good bet for week 2.

[Allseasons-Si]

The Arctic is broke,...