Model Output Discussion - Staying cold into the new year

[Man With Beard]

No point looking beyond D7 now. There are too many potential interacting pieces at D8 and D9. Could go a number of ways, though, if there is an attempt to displace cold, I'd be very surprised if it weren't snowy at first.

Still can't get my head around these rainy easterlies from ECM. I'll shave my beard off if there's no snow from an easterly at this time of year

[Drifter]

This may be a slightly technical question, but here goes. 

How come when a frontal system is approaching from the west, we are told as long as the winds are from east of south, even -1c 850s are sufficient for snow ....

However when we have an easterly as modelled with showers coming in from the east, 850s of -6 are not enough?

Is it something to do with the make up of a frontal system vs convective showers?

[Anthony Burden]

Marco Patanga on Twitter stating major SSW on the cards Glosea 5 agree,could be lookiing

at something very special.models will be all over the place after 168 hrs.

[Tim Bland]

15 minutes ago, Kasim Awan said:

The easterly next week is conducive for snow inland above 100m with uppers of -7, 20-100m at -7.5 and coast under -7.8 ish. Heights higher and this easterly will have a largely adiabatic dew point profile, i.e. a lack of inverted cold surface dew points due to the North Sea run. Surface snow conditions here depends largely on precip intensity & whether a UKMO source verifies which would increase chances in marginal zones. A middle ground option seems more feasible, gfs is not far from this mark so expect marginality with some opportunity. 

Not realistic to make bold snow predictions beyond this, the D7-12 outlook is remaining cold. The magnitude of snow & thus cold at 5 days out is far from resolved so trying to narrow this down at day 8 seems futile.

Perhaps, but this is a forecast, I was stating what the 12 ECM operational was showing. And it wasn’t snow about 100m or all of the costsworlds and chilterns etc would have had snow cover as well as cities like Birmingham. I wasn’t making any bold predictions, just discussing the model output, in this case the ECM run. I hope you are right though as I’m 120asl if you are wrong I shall be sending you the invoice for my skido and snow tyres  

[Cold Winter Night]

Usually with great cold spells, there is a role for North America. Low heights over the Hudson Bay, reinforcing a Greenland/Iceland High.

It's odd to see nothing happening upstream on ECM, GFS, GFSP day 7-10.
I can't recall charts that have shown such fairly strong hights all over the USA, Canada AND the Atlantic. It's as if the weather in that part of the NH has been switched off. Looks weird to me.

Do we have historic examples of similar situations?

[blizzard81]

4 minutes ago, Sweatyman said:

ECM said i should be buried in snow by now according to charts last weekend so i doubt it

Lol I understand your pessimism. I think many will get the snow they crave for. Possibly sooner than they think. This chart coincides with my birthday. What a birthday that would be. I have lived in west yorks all my life and I can count on the fingers of one hand how many of my birthdays have seen a flake of snow. And I was born in the early 70's. Just shows how abysmal our winters have been in the last 4 to 5 decades. I am very hopeful for this one though. 

[Kasim Awan]

Just now, Tim Bland said:

Perhaps, but this is a forecast, I was stating what the 12 ECM operational was showing. And it wasn’t snow about 100m or all of the costsworlds and chilterns etc would have had snow cover as well as cities like Birmingham. I wasn’t making any bold predictions, just discussing the model output, in this case the ECM run. I hope you are right though as I’m 120asl if you are wrong I shall be sending you the invoice for my skido and snow tyres  

My judgement is that even above 100m & in the upper air temps required there would be limitating factors, snow then depends on precip being present. Given the set up on the model output this is likely to be patchy.

[Scott Ingham]

8 minutes ago, Drifter said:

This may be a slightly technical question, but here goes. 

How come when a frontal system is approaching from the west, we are told as long as the winds are from east of south, even -1c 850s are sufficient for snow ....

However when we have an easterly as modelled with showers coming in from the east, 850s of -6 are not enough?

Is it something to do with the make up of a frontal system vs convective showers?

Its not as simple as even what you are saying.

Historically when we have had these events weve had a very cold continent (theyve happened in feb) with lower ssts and dps easily the rights side of marginal and the precipitaion has already been made.

In an easterly like is being modelled its convective (i.e we are creating showers) tje temp differential is created between the upper air temp and temp of the ocean. Our ocean now is very warm so we need colder 850s to create showers. We also need the heights to be cold to help instability (the darker blues and purples) rather than yellows and greens. This also aids instability but at the same time brings the freezing level closer to the suface.

Also we have a diving pressure system from the north.

Juat like a system from the west we dont need high 850s

This is because we arent relying on producing showers off the north sea.

The reason why some saw snow last week is the heights them blues n purples.

They were extreme. So it brought the snowline right down to the surface meaning 850s of -3s and -4s were okay for some areas on the right side of dps temoerature at the time at night and elevation

Edited December 30, 2020 by Scott Ingham

[stodge]

Evening all

A little earlier than usual to take a canter through the evening output. Another chilly day in London and while the SE Regional Thread seems to be full of wailing and gnashing of teeth about the lack of snow for the moment, last night's output suggested we would see some of the white stuff in time.

Onwards and sideways..

12Z GEM: T+120 this evening takes us to next Monday, January 4th. Between a ridge of HP stretching from Scandinavia west and south-west to an HP in mid-Atlantic and an LP in the Gulf of Genoa (where else?), an E'ly airflow covers most of the British isles. Dry for the north you'd think but a possibility of precipitation further south and east. 850s of -4 to -8 widely at this time. On to T+180 and the HP has now established across the British Isles (or rather the ridge has moved a little south). Any residual E'ly influence is confined to the far south and the eye is drawn to a new LP forming to the north-west of Iceland in what looks some very cold air. The airmass over the British Isles remains cold at this time. The LP starts to move south but all that does is pass the HP to the south of the British Isles and allow milder air to move in round the top of the HP which by T+240 is over northern France. Actually, it's not that mild (it is less cold in the south) and there's some colder air filtering into Scotland. It's one of those instances where the 500s and 850s don't tell the same or even the whole story.

12Z GFS OP - an intriguing but slightly disappointing GEM for cold fans and the potential phasing of the Icelandic and Atlantic troughs doesn't augur well so let's hope the GFS OP keeps the faith (if there is such a thing). At T+120 no real surprise with a cold ENE'ly covering most of the British Isles. 850s of -4 to -8. Moving on 60 hours later and not much has changed. NO sign of cyclogenesis over eastern Greenland but a deep LP is moving to the north of Scandinavia. For the British Isles, a light E'ly flow is maintained. 850s not much different by this time. By T+240, the LP has dropped south into Scandinavia and a N'ly flow is passing over or just to the east of the British Isle. Strong heights from the west of Ireland north-west into Greenland by this time. The 850s show a slight easing of the cold but there's some really cold air in that northerly (-20 uppers for those who like that sort of thing). By T+312 the evolution has got messy - the LP has become stationery over the eastern Baltic with come very cold air in its circulation. A slack area of LP sits off the south-west of England with a ridge in mid-Atlantic. The airmass is becoming less cold over the British Isles by this time. By T+384 the cold spell is over and we have a more typical Atlantic profile. 

12Z Parallel -as with last night, the OP lessens the cold spell in mid January and perhaps in tandem with other teleconnections we will see a brief easing of cold in the middle of the month. The T+120 has no surprises on the Parallel. From there, the divergences begin and by T+180 the British Isles are in a pincer between LP moving up from the south and another LP moving down from the north-west. The airmass over the British Isles at this time remains cold with -8 850s widely. As expected, the two LP systems phase over the British Isles with the LP from the north-west sinking south into France and keeping the air flow from the east. There's a bit of mixing out of the cold uppers by T+240 but I think you'd be looking at a lot of snow from this feature. From there, the trough remains a complex and dominant feature with a new LP developing to the south-west of Iceland and another feature approaching the south-west of Britain at the same time. Less cold air is steadily moving in from the south west but it remains cold over northern and eastern parts. By T+384, as with the OP, the Atlantic is back in charge. 

12Z ECM - so more output suggesting an easing of cold in mid-month. On then to ECM and at T+120 no surprises but the 850s are uninspiring so for fans of cold sleet or rain great news - I'm NOT going there. By T+192, the HP has receded west and a complex trough covers the British Isles with centres to the north and south-east. Some very cold air in the vicinity but not so much over the British Isles - however, still a cold airmass to work with for fans of snow. From there, a dominant centre forms, deepens and runs south to be over Ireland by T+240. By then, the less cold sector is over southern Britain but the airmass remains on the cold side and the big question is where that LP will go from there. If it runs south into France, there's plenty of cold air to the east and north.

Looking elsewhere, 12Z Control goes milder in FI for southern areas but cold remains close by and never really leaves the north before returning south but it's another messy evolution. 

As for the 10HPA charts - 12Z OP initially splits the PV at T+114 but Dr Who-like, it regenerates before coming under a new assault in FI which renders it weak and vulnerable by T+384. 12Z Control achieves the split at T+336. Parallel achieves the initial split at T+78 and a further split in FI. 

Conclusion - a greater degree of uncertainty than for many days in the models tonight. FI starts at T+144 and the evolutions from there are many and varied. What will happen to the north and north-west in terms of cyclogenesis seems to be the new question or theme of the night (and we seem to have a different "theme" each evening). GFS ends the cold spell by mid month from the west. ECM certainly keeps things interesting and GEM is uncertain. The evolution from T+144 to T+240 looks fraught with uncertainty tonight.

[blizzard81]

6 minutes ago, Man With Beard said:

No point looking beyond D7 now. There are too many potential interacting pieces at D8 and D9. Could go a number of ways, though, if there is an attempt to displace cold, I'd be very surprised if it weren't snowy at first.

Still can't get my head around these rainy easterlies from ECM. I'll shave my beard off if there's no snow from an easterly at this time of year

I agree with your comments about the easterly. I cannot recall such a potent 'looking' easterly in January not being cold enough for snow. I can't remember one. I hope I will be saying the same thing by this time next week

[Djdazzle]

7 minutes ago, Kasim Awan said:

Without getting scrutinized I would say many on here are experiencing reflex reactions to single operational runs.

These runs are part of a bigger computational modelling of the atmosphere at this time. This forms a collective range of possible surface conditions, within which the OP presumes a certain spot. There a plenty of other solutions modelled - and the fact is all look cold / hold snow potential. So the general computation remains cold & potentially wintry in places, using an ensemble logic my judgement is that it's looking positive from a snow perspective. 

It works both ways though - it’s annoying when people over scrutinise operational runs at long range, yet it’s also annoying when folks make comments about places being buried. This is not a dig at you in particular.

[Kasim Awan]

4 minutes ago, Drifter said:

This may be a slightly technical question, but here goes. 

How come when a frontal system is approaching from the west, we are told as long as the winds are from east of south, even -1c 850s are sufficient for snow ....

However when we have an easterly as modelled with showers coming in from the east, 850s of -6 are not enough?

Is it something to do with the make up of a frontal system vs convective showers?

Yes, continued light winds & heavy precip erode the thermal gradient from top > down so essentially it is cold to the surface & the same temp as 4500ft above. This happens via diabatic & evaporative cooling.

Whereas in showers (ignoring streamers), there is usually a lack of precip intensity to produce this cooling, so the air at the surface remains warm, meaning uppers have to be cold enough to produce a baseline surface level dew point of freezing without evap cooling. This is the set up we have next week, so the two key parameters are uppers & dew points.  

[Mike Poole]

3 minutes ago, Anthony Burden said:

Marco Patanga on Twitter stating major SSW on the cards Glosea 5 agree,could be lookiing

at something very special.models will be all over the place after 168 hrs.

Yep, but we’ve known it was Jan 5th for some time now! 

I am so looking forward to see what happens, the build up to this has equalled that before the 2018 SSW, it isn’t just about the actual sudden warming in the strat, all we are experiencing and the models are showing are related to the upcoming SSW event.  It would be a mistake to just look at the strat data alone, this winter is unusual by every measuring stick!  

[stodge]

29 minutes ago, phil nw. said:

With such differences after day 5 it may be wise not too over analyse later operational charts at this point. 

I believe the pattern is still evolving but we can see enough from the general nh set up and ens. trends that we face a cold and wintery outlook. 

I am happy with the shorter term. 

They are all showing colder uppers from day 3 and the onset of the easterly by Sunday. 

It is a good trend and knowing the pv is a badly wounded beast should keep us optimistic that we are likely to be in a blocked Atlantic pattern for some time.

I wish you'd told me this before I started doing my nightly analysis !!

I do agree the degree of uncertainty from T+144 to T+240 in particular is very high tonight. A couple of days ago it was all about LP moving up from the south and interacting with the cold block but now it's become more complex with LP coming down from the north and phasing with the European trough over the British Isles.

I really don't know tonight.

[Drifter]

4 minutes ago, Kasim Awan said:

Yes, continued light winds & heavy precip erode the thermal gradient from top > down so essentially it is cold to the surface & the same temp as 4500ft above. This happens via diabatic & evaporative cooling.

Whereas in showers (ignoring streamers), there is usually a lack of precip intensity to produce this cooling, so the air at the surface remains warm, meaning uppers have to be cold enough to produce a baseline surface level dew point of freezing without evap cooling. This is the set up we have next week, so the two key parameters are uppers & dew points.  

Great answers - thanks and also to Scott. 

Edited December 30, 2020 by Drifter

[Methuselah]

4 minutes ago, Anthony Burden said:

Marco Patanga on Twitter stating major SSW on the cards Glosea 5 agree,could be lookiing

at something very special.models will be all over the place after 168 hrs.

You've it the proverbial, AB... From memory, aren't the models always apt throw wobblies, when an SSW is incoming?

The arguments over marginality seem, to me, to be getting a tad silly: the upcoming spell will cause even the professionals 'tense, nervous headaches'... So, where does that leave us -- look out of the window?

[Essexfish]

Specifically mentions what the models are picking up and explains why next week is likely to be cold and wet rather than cold and white.

[Froze were the Days]

6 minutes ago, Anthony Burden said:

Marco Patanga on Twitter stating major SSW on the cards Glosea 5 agree,could be lookiing

at something very special

Well nothing 'very special' is showing in the models in terms of deep cold and widespread snow, yes blocked and no rampaging PV in sight with snow chances in places...but considering how blocked it is and what is happening outside my doorstep and no doubt many others is another thing altogether.

It sure is draining all this model watching (it is fatiguing) and we're only just a 1/3 through Winter!

[Cuban Zebra]

6 minutes ago, blizzard81 said:

I agree with your comments about the easterly. I cannot recall such a potent 'looking' easterly in January not being cold enough for snow. I can't remember one. I hope I will be saying the same thing by this time next week

Coming from just down the road to you a potent easterly stacks it up against the Pennines and means a dumping for us.

FWIW I think we’re in the draw for something memorable!!

[SMU]

30 minutes ago, Daniel* said:

Still sourced from eastern med on ARPEGE they’re really not that different at all. 

 

and thanks @Mr Frost people talk about snow starved they have no idea.. it’s coming up 3 years since my part of London has seen laying snow. Could very easily be negative and cynical but that’s not healthy. I understand it’s also important to be realistic, but in this hobby you always need to try to find some positives or you’ll go mad! 

Hi bud thats slightly incorrect 

The kink prevents the mixing

UKMO V ECM

[Lampostwatcher]

3 minutes ago, Essexfish said:

Specifically mentions what the models are picking up and explains why next week is likely to be cold and wet rather than cold and white.

No point taking to much notice of a 10 day trend 

When there warnings for the South were removed today for this evening

[Daniel*]

36 minutes ago, Neilsouth said:

The low pressure system that traversed towards the south and then towards the South East never happened, it went into the channel, pretty much a changing forecast day by day even upto the day before. Yet here we are looking towards the weekend and next week. We are struggling to look towards our own lands, yet we try to look beyond what's happening across the world? Hmmm

I think there’s a difference however between a low pressure system which is volatile and easterly flow which we WILL see, while the depth of cold and precip remains unresolved so it seems quite premature to say x, y and z. It’s understandable people are talking about it, it does form model output discussion after all.

Edited December 30, 2020 by phil nw.

[Mike Poole]

ECM ensembles.  Well where do you start:

T168:

That’s the GFS op solution boiled then, that won’t happen - good!

T192:

The dying cat vortex analogy very much holds here.

T240:

Will it now get through to people that there is no rubbish weather, none at all, coming off the Atlantic, or from the USA, or from a ‘west-based -NAO’.  

Regards to everyone

Mike

 

[sheikhy]

I think we gona see upgrades on the 18z and the uppers will look better tomorrow on the ecm!!!

[iceman1991]

21 minutes ago, Anthony Burden said:

Marco Patanga on Twitter stating major SSW on the cards Glosea 5 agree,could be lookiing

at something very special.models will be all over the place after 168 hrs.

Ho Anthony burden How reliable is this guy about outcomes ?