Model output discussion - Closing in on Christmas

[Matt H]

Brilliant to see hardly any of the GEFS 12z ensemble members heading above 0C after Christmas, definitely a seasonal feel on the way soon.

[ICE COLD]

Just caught up . Stunning output across the board just stunning . The uppers are not to great tho . And if these charts below come of Jan , Feb and March are gonna be mental on here . 

[Eskimo]

1 minute ago, Frosty Winter said:

Brilliant to see hardly any of the GEFS 12z ensemble members heading above 0C after Christmas, definitely a seasonal feel on the way soon.

That's the tightest set of ens I've seen in some time.

[Captain Shortwave]

 

I know it is a temporary set up, but I would love a set up like this to occur. Strong northerly winds (possibly close to gale force near the coasts) and warm SSTs that can drive heavy and frequent snow showers into eastern areas with significant accumulations . It has been a long time since a proper snow event that came from a northerly like the one shown (probably over fifteen years and that was when I was living in eastern Suffolk).

 

Note that the GEM tends to over-modify 850s from maritime sources so they would likely be a little lower that what is shown.

Edited December 20, 2020 by Captain Shortwave

[That ECM]

Chart of the day  and ECM just making sure tail is firmly between legs before coming out.

7D70B3AB-3533-488F-9F16-4B3C304AA3E2.webp

[Kasim Awan]

Just now, Captain Shortwave said:

 

I know it is a temporary set up, but I would love a set up like this to occur. Strong northerly winds (possibly close to gale force near the coasts) and warm SSTs that can drive heavy and frequent snow showers into eastern areas with significant accumulations . It has been a long time since a proper snow event that came from a northerly like the one shown (probably over fifteen years and that was when I was living in eastern Suffolk).

GFS mean actually suggests the suite somewhat favours this more straight line northerlt solution. Given the ECM is also more easterly in the placement, the GEM is a reasonable middle ground.

[I remember Atlantic 252]

2 minutes ago, Captain Shortwave said:

 

I know it is a temporary set up, but I would love a set up like this to occur. Strong northerly winds (possibly close to gale force near the coasts) and warm SSTs that can drive heavy and frequent snow showers into eastern areas with significant accumulations . It has been a long time since a proper snow event that came from a northerly like the one shown (probably over fifteen years and that was when I was living in eastern Suffolk).

Classic wishbone, reminds me of my childhood, miss out on the snow here, but used to be below zero max, loads snow down E coast

Edited December 20, 2020 by I remember Atlantic 252

[Optimus Prime]

10 minutes ago, dragan said:

May i be so bold as to ask.....

What is the reason people think the -4ish uppers will actually be colder than that (if these charts verify of course) 

Is it past experience? Genuine question 

Conjecture.

Sometimes they get upgraded, sometimes they don't. Models do seem to be better these days at predicting upper atmospheric temperatures more than 5 days out, but ultimately the resolution fine tunes incrementally, it doesn't just suddenly get sharper and more accurate at a prescribed benchmark.

Northerlies do require lower temperatures at that height because they are passing over a modifying ocean. Easterlies also get modified by the north sea, but to a much lesser degree and I believe there is more tolerance to producing snowfall at comparatively similar temperatures. 

Edited December 20, 2020 by Optimus Prime

[SLEETY]

7 minutes ago, Frosty Winter said:

Brilliant to see hardly any of the GEFS 12z ensemble members heading above 0C after Christmas, definitely a seasonal feel on the way soon.

And the operational was as the top end,so much colder uppers than the op are showing strong still which is good news..

[Chesil View]

2 minutes ago, SLEETY said:

And the operational was as the top end,so much colder uppers than the op are showing strong still which is good news..

Indeed so Sleety.

[Catacol]

41 minutes ago, s4lancia said:

Irrespective of Arctic warming, climate change, things were better back in the 1700s blah blah blah, there are very simple synoptic reasons why the uppers are what they are. Nothing weird or sinister or strange  or ‘typical’ , the current Northern Hemispheric set up is why.  

Patience. Very cold uppers rarely arrive at the start of an emerging cold spell. The potential is there IF you want to see it.

And whilst I can barely be bothered to say it again, 850s are, as you know, only a part of the will it snow equation anyway...

Yes - and I’ll add that it very rarely goes from mild to cold in a day. We are currently mild. The ground is warm and also wet. We are going to need several days of cold and frost to chill our context a bit. The good news is that at this time of year there is no better moment for local conditions to support developing cold.

[Scott Ingham]

1 minute ago, Catacol said:

Yes - and I’ll add that it very rarely goes from mild to cold in a day. We are currently mild. The ground is warm and also wet. We are going to need several days of cold and frost to chill our context a bit. The good news is that at this time of year there is no better moment for local conditions to support developing cold.

A week under that trough at this time of the year will reduce the snow line. I have no doubts. Any snow and well have a feedback mechanism creating a local cold pool

[northwestsnow]

2 minutes ago, Catacol said:

Yes - and I’ll add that it very rarely goes from mild to cold in a day. We are currently mild. The ground is warm and also wet. We are going to need several days of cold and frost to chill our context a bit. The good news is that at this time of year there is no better moment for local conditions to support developing cold.

Interestingly,(and not wanting to get into a debate about uppers)further inspection of GFS 12Z shows temps,esp the further North you head, very suppressed throughout, despite the less then impressive uppers.

 

[Battleground Snow]

Based on historical patterns, you would say the GFS will model the trough as more of a shallow feature nearer the time, which would mean colder uppers, but less precipitation.

Ecm will be interesting, I think it will be Inbetween the gem and GFS, which may be a very good outcome for coldies.

 

[Devonshire]

13 minutes ago, Captain Shortwave said:

Strong northerly winds (possibly close to gale force near the coasts) and warm SSTs that can drive heavy and frequent snow showers into eastern areas with significant accumulations .

Is this likely to affect only East coast - or are we likely to see the fabled Pembroke Dangler? (apologies in advance if dangler is not on the dictionary )

[Jason M]

10 minutes ago, Frosty Winter said:

My point wasn’t about arguing against the importance of uppers in delivering snowfall, indeed all of the factors that are required to produce snowfall are important and need to be discussed. I was just saying that the same people appear after every model run to moan and make the same point that they made only a few hours ago. If you aren’t impressed with the model output then it’s obviously perfectly acceptable to make a post about why you feel that way but people are more than capable of coming to their own conclusions without the same people posting the same message every few hours. I just don’t understand why you would feel the need to repeat yourself if you’ve already made the same point countless times already.

Because people are referring to a new set of outputs. Also its perfectly acceptable to repeatedly claim its going to snow (even on occasions when this simply isn't supported by the facts). This place can become an echo chamber sometimes and hence the crushing depression that falls once peeps realize the promised snow isn't coming! There is no one who wants snow more than me and when I see it in the charts I'll be ramping it up with the best of them.

If anyone wants an objective view just think about the people who are not posting right now. Sometimes that can be as informative as anything that actually gets typed.

This scenario is a forecasters nightmare and will be a nowcast in reality. One area that I can pick out as 'not favored' in this set up is EA & SE England as these areas will always tend to get colder air in last. I say that with a heavy heart as its where I live but that's the way the cards fall. Hopefully an SSW delivers a nice easterly in early Jan to compensate .

 

[Duane S.]

30 minutes ago, Optimus Prime said:

Except what you've just outlined goes completely against the science. The air in the Arctic is much warmer than it was even 20 years ago. And >40 years ago temperatures would be 1.0 - 2.5° C colder in the arctic regions. It's just a fact and this translates to less cold northerlies when the synoptics grant it.

Yes, undeniably the Arctic is warmer and undeniably that doesn’t help achieve slightly colder uppers but that, I thought quite clearly, wasn’t my point. The main reason the uppers aren’t lower than they may’ve been is mainly Synoptics.

But yes, obviously, a warming Arctic will only work against us in terms of temperatures.

[dragan]

20 minutes ago, Broadmayne blizzard said:

Because years of model watching experience have shown us that models have a tendency to underplay uppers the further away from t0 you go.

thanks for that, i mean it does seem strange the level of non existent -5 or below uppers. 

[Guest]

4 minutes ago, northwestsnow said:

Interestingly,(and not wanting to get into a debate about uppers)further inspection of GFS 12Z shows temps,esp the further North you head, very suppressed throughout, despite the less then impressive uppers.

 

Almost like there are other factors in play

[Kasim Awan]

 

1 minute ago, Devonshire said:

Is this likely to affect only East coast - or are we likely to see the fabled Pembroke Dangler? (apologies in advance if dangler is not on the dictionary )

All depends on the size & location of the low. Shortwave central as per a more UK based centre would limit North Sea shower potential and moderate uppers potentially leading to a poorer situation for you. I would prefer a straight northerly run for the immediate east coast anyway.

[BARRY]

2 minutes ago, Devonshire said:

Is this likely to affect only East coast - or are we likely to see the fabled Pembroke Dangler? (apologies in advance if dangler is not on the dictionary )

[Djdazzle]

Good looking charts, that’s for sure.

Bur remember: there’s still so much that could go wrong!

[Kasim Awan]

1 minute ago, Valleyboy said:

Just lowland rain and hill snow.

If the low size reduces a bit, expect a more favorable synoptic for short wave development. Under the heights evap cooling would easily allow for snow. Don't forget the 528 DAM is covering the UK - the 4th Dec 2020 event only had -2 uppers.

[AmershamMike]

3 minutes ago, Valleyboy said:

Just lowland rain and hill snow.

Wow, you’re a bundle of laughs.

[iowpompeylee]

7 minutes ago, BARRY said:

Usually these will drift inland, on a nice cold brisk breeze. All to play for!