Model output discussion - The run up to Christmas

[Tim Bland]

GEM has -8 uppers and snow for most next week...

[Ventnor Viking]

From the 252hr NH view onwards on this run you can begin to see a HP over northern Russia start to retrogress (move from east to west) into northern Scandi. This is very common when the Jet weakens. This will be something that really catches my eye as the likely scenario would be to retrogress to Greenland/Iceland and draw in some very cold air from Siberia, even the uppers would be cold  

Edited December 21, 2020 by Ventnor Viking

[snowblind]

7 minutes ago, Geordiesnow said:

Yep the initial upper air temperatures have marginally upgraded in the past few days and whilst the window for convective showers is small, there should definately be some heavy snow showers down eastern areas. Whether any will settle during daylight hours is debatable but some parts in the east could well wake up to a covering of snow on Xmas day. 

As for the 2nd event, well I'm a bit more underwhelmed and a lack of cold air could well be an issue here, just typical there was no real PV over Greenland before the forecast ridge because if there was, the uppers are bound to be colder. Like at the start of the month, we are feeding on scraps unfortunately and perhaps a set up 40 years ago would deliver more than what the models are currently showing. Still time for upgrades(and downgrades) mind but you can't hide behind the fact a good set up is no good if the air is not cold enough. 

I remember a similar situation in the mid 90's. Boxing day 95 or 96 I think. It was fairly cold over Christmas and I remember a few well scattered wintery showers being forecast for the evening overnight period. I was living in Hemel Hempsted in Herts and working in Brentwood, Essex at the time. Driving to work via the M25 on the morning of the 27th December there was some areas of snow that I went through but it wasn't that extensive. As I neared the Brentwood turn off there was a bit more in the way of snow, a few inches. The road climbs steadily from the M25 junction to the town itself which is about 100m asl. When I got to the town I couldn't belive how much snow there was - a good 8 inches. It was pretty crazy. Apparently one of the well scattered snow showers had become particularly slow moving over the town and dumped loads of snow. I guess the slight elevation helped.

[WxHerts]

Anyone know when GEM got its warm 850hpa temp bias fixed?

[Vikos]

3 minutes ago, Ventnor Viking said:

From the 252hr NH view onwards on this run you can begin to see a HP over northern Russia start to retrogress (move from east to west) into northern Scandi. This is very common when the Jet weakens. This will be something that really catches my eye as the likely scenario would be to retrogress to Greenland/Iceland and draw in some very cold air from Siberia, even the uppers would be cold  

 

QBO goes easterly, a common signal for cold spells in northern europe, due a weak jet. That's one of the good news of todays rampage...

Edited December 21, 2020 by Vikos

[Mair Snaw]

1 minute ago, snowblind said:

I remember a similar situation in the mid 90's. Boxing day 95 or 96 I think. It was fairly cold over Christmas and I remember a few well scattered wintery showers being forecast for the evening overnight period. I was living in Hemel Hempsted in Herts and working in Brentwood, Essex at the time. Driving to work via the M25 on the morning of the 27th December there was some areas of snow that I went through but it wasn't that extensive. As I neared the Brentwood turn off there was a bit more in the way of snow, a few inches. The road climbs steadily from the M25 junction to the town itself which is about 100m asl. When I got to the town I couldn't belive how much snow there was - a good 8 inches. It was pretty crazy. Apparently one of the well scattered snow showers had become particularly slow moving over the town and dumped loads of snow. I guess the slight elevation helped.

Remember that very well, i was living in Romford at the time and we had nothing, visited a friend in brentwood and as you say very deep snaw..

[Ventnor Viking]

3 minutes ago, Vikos said:

 

QBO goes easterly, a common signal for cold spells in northern europe, due a weak jet. That's one of the good news of todays rampage...

Exactly, as we head in to FI it waters that scenario down, however I fully expect that to strengthen on the next few runs and to see no return of zonal conditions, as FI shows for the foreseeable. 

[Mike Poole]

6 minutes ago, WxHerts said:

Anyone know when GEM got its warm 850hpa temp bias fixed?

GEM was upgraded quite significantly, I think just before last winter.  It was when it started coming out daily later than GFS, previously they came out about the same time.  Since it has often been vying with GFS to be the 3rd best model.  

[Vikos]

2 minutes ago, Ventnor Viking said:

Exactly, as we head in to FI it waters that scenario down, however I fully expect that to strengthen on the next few runs and to see no return of zonal conditions, as FI shows for the foreseeable. 

Zonal-ITY (  ) =

We will stay in a longer phase of meridional amplitudes, with more colder spells and less mild ones. Once settled, this will be quite perisstent, as long enough cold builds up over east europe / russia

[Methuselah]

I think the Uppers might be too high?

    

But then, on the other side of the cliché, things could be well primed for a BFTE post-SSW?

    

Edited December 21, 2020 by General Cluster

[booferking]

You can see clearly from the last 3 gfs 12z runs that the low has trended south east run by run which is a good thing,  only detail that might be a bit of a worry is the Atlantic high pressure ridging into greenland has reduced a good bit but if it maintains and doesn't reduce over the coming runs then reloads should be locked in.

Edited December 21, 2020 by booferking

[Allseasons-Si]

The GEM ends on an interesting note,look at the Urals block,that would advect colder air SW.

[TSNWK]

1 minute ago, booferking said:

You can see clearly from the last 3 gfs 12z runs that the low has trended south east run by run which is a good thing,  only detail that might be a bit of a worry is the Atlantic high pressure ridging into greenland has reduced a good bit but if it maintains and doesn't reduce over the coming runs then reloads should be locked in.

Agreed I think it was yesterday we talking about west nAo and corrections east.. we have that now and need to stop that trend going forward....I’m enjoying the attempts recent runs to link up heights from the west and east above pushing the trough through to the south and leaving us locked into a draw from and easterly quarter.. never quiet makes it on past couple of runs.. but interesting all the same..

[Jeremy Shockey]

GFS 12 z ensembles 850 s

850's are -8 or even colder for 24th / 25th

[Allseasons-Si]

Control day ten...

[ITSY]

Without meaning to skirt over the obvious potential 120-192, almost all of the GEFS give serious weight to an FI reload of sorts, particularly in the North Atlantic. 

This is the mean at +240 - up she goes again...

[MATTWOLVES 3]

Wow its gone quiter in here...take a look at the GFS precipitation graphics next week...plenty of snow to the North and a risk showing up around Central and SE parts...you Londoners will be driving on the Thames before you know it.. Im not gerrin to excited just yet, I just need to keep cool and get ready to run the risk of being disappointed.

[northwestsnow]

UKMO 144 NH view...

[Updated_Weather]

Something interesting from Matt Hugo - regarding MJO

[Drifter]

3 minutes ago, northwestsnow said:

UKMO 144 NH view...

Perfection.

Edited December 21, 2020 by Drifter

[Weathizard]

Surely for many places -4 in the depths of winter with sub 528 thickness could still deliver snow? Providing a few other factors are favourable (offshore wind etc)
 

It brings me back to a few things some of the older members have said, many many memorable snow events in the past had less than impressive uppers.

My gut feeling tells me they will continue upgrading anyway, I’d love to have the energy to go back to last week and see what the upper temps predicted were for Christmas Eve, I’m almost certain they weren’t between -8&10 in places.

[Updated_Weather]

4 minutes ago, MATTWOLVES said:

Wow its gone quiter in here...take a look at the GFS precipitation graphics next week...plenty of snow to the North and a risk showing up around Central and SE parts...you Londoners will be driving on the Thames before you know it.. Im not gerrin to excited just yet, I just need to keep cool and get ready to run the risk of being disappointed.

Always loved that GIF xD

[Kasim Awan]

3 minutes ago, MATTWOLVES said:

Wow its gone quiter in here...take a look at the GFS precipitation graphics next week...plenty of snow to the North and a risk showing up around Central and SE parts...you Londoners will be driving on the Thames before you know it.. Im not gerrin to excited just yet, I just need to keep cool and get ready to run the risk of being disappointed.

Yes, from experience the set up screams rain to snow event potential to lower levels. Throw in stalling, an offshore breeze, nocturnal cooling & heavy ppn. Some decent amounts on the cards locally.

All snow for most >200m with -4.5 uppers at 525DAM.

Not everywhere will see the precip.

[Updated_Weather]

Just now, Kasim Awan said:

Yes, from experience the set up screams rain to snow event potential to lower levels. Throw in stalling, an offshore breeze, nocturnal cooling & heavy ppn. Some decent amounts on the cards locally.

All snow for most >200m with -4.5 uppers at 525DAM.

Not everywhere will see the precip.

Remember the early December 2020 snowfall we had here in Essex, how marginal that was and the uppers wasn't that cold.. But because of the heavy PPN, we got a good covering.. But a few miles away, absolute nothing.

[Kasim Awan]

Just now, Updated_Weather said:

Remember the early December 2020 snowfall we had here in Essex, how marginal that was and the uppers wasn't that cold.. But because of the heavy PPN, we got a good covering.. But a few miles away, absolute nothing.

This upcoming set up is less marginal on average. The "base" snow line will be ~150m lower than 4th Dec if the current output is correct. This means more places will come into the snow potential, and snow will be easier to achieve. Potential is the key operator here.