Model output discussion - Closing in on Christmas

[northwestsnow]

Hopefully the upcoming period will assist lowering both sea temps and ground temps ...

Personally the period between Christmas to mid Jan is prime time insofar as winter is concerned... the short days mean solar input is low, just need some snow-covered landscapes...

I'm confident elevated Northerly locations will see intermittent coverings of snow in the coming weeks but low lying areas could remain snowless  out to early Jan as it stands, I'm not much better off, I've had a day, and it had melted by nightfall.  

Fingers crossed we see upgrades over the coming days, it will be brill to have a cold Christmas eve this time round...

 

[Snowy Hibbo]

https://longrangesnowcenter.net/2020/12/20/europe-on-the-long-term-20th-dec/

Climate drivers looking interesting for a cold and snowy late December and early-mid January for the UK, with the potential of a SSW or similar, good extratropical conditions and an already negative AO in the troposphere  

[damianslaw]

Christmas period (24-26th), now coming into the reliable, I'll be giving some general views about likely prospects this evening, these can only be initial, firmed up tomorrow, and by Tuesday more definitively.

Based on current synoptics, the trend is colder through the coming week, and longer term nothing to suggest any significant mild reload, opposite if anything.

Thinking back to the last 10 years or so, there hasn't been a christmas since 2010 when we had prospects of temperatures at least a bit below average (yes can't compare this year to 2010), but its refreshing not to be looking at a raging atlantic bringing likely heavy rain, gales and constant mild temperatures. Gosh just a bit of frost will be very welcome.

[Howie]

6 minutes ago, Allseasons-si said:

That's an impressive gefs 06z mean.

I'll say no more 

A good portion of the ensembles below the mean

[bumpydogz]

8 minutes ago, Howie said:

A good portion of the ensembles below the mean

50% of them maybe? 

[Jason M]

7 minutes ago, Howie said:

A good portion of the ensembles below the mean

Yes. Actually a good number of easterlies in amongst them from day 9 onwards. Not many 'beasterlies' but certainly a good few that would be cold enough. 

-6 at 850 level in a continental airmass is a different story completely. Can achieve an ice day with that (especially in late Dec early Jan), whereas in a day 2 PM airmass 5-6c is often achievable. 

[Howie]

8 minutes ago, bumpydogz said:

50% of them maybe? 

 

4 minutes ago, Jason M said:

Yes. Actually a good number of easterlies in amongst them from day 9 onwards. Not many 'beasterlies' but certainly a good few that would be cold enough. 

-6 at 850 level in a continental airmass is a different story completely. Can achieve an ice day with that (especially in late Dec early Jan), whereas in a day 2 PM airmass 5-6c is often achievable. 

Looking good

[terrier]

Well I’ve got to say looking at the 850s on the gfs output it looks like for the majority of the U.K. we would be looking at cold rain for the vast majority of us.  And just seen the weather for the week ahead and temps for Xmas day we are looking at between 6c in the north and 8c in the south so pretty standard fair to be honest. Still think into the new year could be our best shot that’s if the ssw works in our favour fingers crossed. 

[northwestsnow]

3 minutes ago, terrier said:

Well I’ve got to say looking at the 850s on the gfs output it looks like for the majority of the U.K. we would be looking at cold rain for the vast majority of us.  And just seen the weather for the week ahead and temps for Xmas day we are looking at between 6c in the north and 8c in the south so pretty standard fair to be honest. Still think into the new year could be our best shot that’s if the ssw works in our favour fingers crossed. 

I suspect they will be nudged down a degree or two for 24th/25th ...

[MATTWOLVES 3]

I think we have lift off with those 6z ensembles..plenty of em throwing a treat or 2 our way..we just need this to carry on building momentum now,and for those boys down Lands End way to show a little more enthusiasm for us coldies

[Guest]

7 minutes ago, terrier said:

Well I’ve got to say looking at the 850s on the gfs output it looks like for the majority of the U.K. we would be looking at cold rain for the vast majority of us.  And just seen the weather for the week ahead and temps for Xmas day we are looking at between 6c in the north and 8c in the south so pretty standard fair to be honest. Still think into the new year could be our best shot that’s if the ssw works in our favour fingers crossed. 

As has been mentioned before though, 850s are just one of many elements factored in when forecasting snow. Those calling cold rain based purely on underwhelming 850s are being basic in their analysis.

Furthermore, temps of 6-8C are, at the time of writing based on current model guidance, a degree or two too high. I suspect 4-5C widely and 6-7C around coasts with a fairly significant windchill.

Edited December 20, 2020 by Steel City Skies

[Battleground Snow]

It looks like the Russian high will be back around the turn of the year according to the GFS mean. Can it be friend rather than foe this time around? On a positive note this may help with the potential SSW.

[northwestsnow]

5 minutes ago, Steel City Skies said:

As has been mentioned before though, 850s are just one of many elements factored in when forecasting snow. Those calling cold rain based purely on underwhelming 850s are being basic in their analysis.

Furthermore, temps of 6-8C are, at the time of writing based on current model guidance, a degree or two too high. I suspect 4-5C widely and 6-7C around coasts with a fairly significant windchill.

The slacker the flow the better...

We want that big trough dropping through at 144 to do so as quickly and as far south as possible...

[northwestsnow]

2 minutes ago, Battleground Snow said:

It looks like the Russian high will be back around the turn of the year according to the GFS mean. Can it be friend rather than foe this time around? On a positive note this may help with the potential SSW.

looks slack, and quite cold for Europa...

[BlueHedgehog074]

25 minutes ago, damianslaw said:

Christmas period (24-26th), now coming into the reliable, I'll be giving some general views about likely prospects this evening, these can only be initial, firmed up tomorrow, and by Tuesday more definitively.

Based on current synoptics, the trend is colder through the coming week, and longer term nothing to suggest any significant mild reload, opposite if anything.

Thinking back to the last 10 years or so, there hasn't been a christmas since 2010 when we had prospects of temperatures at least a bit below average (yes can't compare this year to 2010), but its refreshing not to be looking at a raging atlantic bringing likely heavy rain, gales and constant mild temperatures. Gosh just a bit of frost will be very welcome.

Nice post. (To be fair the quality of posts in here have continued to be good).

Although the amount of amplification we could get after Christmas Day is still being resolved, a chance though we could see further chilly conditions, personally makes me glad we’re not in the same place at the moment of last Winter. 

Just an example from both today’s and yesterday’s 00Z GFS runs for Sunday evening again next week, and the similarities between them are quite rather impressive. Still maintaining a highly amplified signal upstream in the Atlantic, and a deep UK upper trough.

Yesterday’s 06Z GFS

Today’s 06Z GFS

Today’s 06Z GFS is a little less amplified, some Low Pressure also trying to go over the top of the Western UK ridge across Northern Greenland. It’s consistency overall has been good. 

Some fence sitting would still be worth it until some of the other models such as the GEM come on board. Not impossible for the GFS to become flatter, but it does seem to be sticking to its ideas. The ECMWF has stepped up a bit with a bit more amplification of the Atlantic ridging in its run compared to yesterday, seemingly making somewhat of a move towards the GFS, which is encouraging. I think that halfway house between the GFS and ECMWF could be where we go. Quite often the case with these things really. Something a lot on here would probably be satisfied enough with. Guess we’ll see how things keeping shaping up

[Kasim Awan]

1 hour ago, Jason M said:

Yes. Actually a good number of easterlies in amongst them from day 9 onwards. Not many 'beasterlies' but certainly a good few that would be cold enough. 

-6 at 850 level in a continental airmass is a different story completely. Can achieve an ice day with that (especially in late Dec early Jan), whereas in a day 2 PM airmass 5-6c is often achievable. 

There would be no surface inversion in the modelled set up. In normal lapse rates -6 uppers, in a convective set up, would produce surface temps at 150ft of roughly 3C by day & 0C by night and a freezing level of 380m. This would definitely be somewhat marginal for areas below around 400ft/120m. Bear in mind heavy ppn would effectively remove the top-down lapse rate to near 0 eroding the >0c layer. This would produce a lower snow line..

I also want to clear up confusion about the word zonality and the whole concept of it.

When I used the word "zonal" this morning, I was not describing a positive nao / westerlies.. I was refering to zonality as an index which is how many refer to it as. So any increase in zonality does not instantly mean roaring westerlies, instead any change in part of the pattern which increaes the % of westerly vectors on the map for the area being described as having a zonal tendency. This is where the distinction between "zonal" and "zonal component" is made. The movement of low pressure out of south west GL for example as modelled on the ECM at day 9-10 is an example of an embedded zonal component in a reversed environment. This is localized zonality,, not "zonal" conditions.

I also made no reference to surface conditions, which may even benefit from the greater values projected for the zonal component around Greenland adding in instability to the cold air mass. The ECM/ GEM still have this polar jet injectio, though it has been phased out a little. So still not 100% keen on the GFS Greenland solution but the option is there.

 

Edited December 20, 2020 by Kasim Awan
Need to include evap cooling info

[northwestsnow]

5 minutes ago, Kasim Awan said:

There would be no surface inversion in the modelled set up. In normal lapse rates -6 uppers would produce surface temps of roughly 3C by day & 0C by night and a freezing level of 380m. This would definitely be somewhat marginal for areas below around 250ft/75m.

I also want to clear up confusion about the word zonality and the whole concept of it.

When I used the word "zonal" this morning, I was not describing a positive nao / westerlies.. I was refering to zonality as an index which is how many refer to it as. So any increase in zonality does not instantly mean roaring westerlies, instead any change in part of the pattern which increaes the % of westerly vectors on the map for the area being described as having a zonal tendency. This is where the distinction between "zonal" and "zonal component" is made. The movement of low pressure out of south west GL for example as modelled on the ECM at day 9-10 is an example of an embedded zonal component in a reversed environment. This is localized zonality,, not "zonal" conditions.

I also made no reference to surface conditions, which may even benefit from the greater values projected for the zonal component around Greenland adding in instability to the cold air mass. The ECM/ GEM still have this polar jet injectio, though it has been phased out a little. So still not 100% keen on the GFS Greenland solution but the option is there.

 

Nice Post again.

This is the kind of setup that sees local hills do  well...

I posted earlier, hills across much of Northern England, moreso towards Scotland will,or could see some snowy weather in the coming weeks...

 

[Mucka]

(I just realised I posted this in the moans & ramps thread by accident this morning instead of here)

Is your glass half full or half empty?

The models have now firmed up on a post Christmas cold spell (Half full) but we are not seeing a classic prolonged cold spell of weather programmed by any means yet. (Half empty)

Based on current output.

We should begin to draw in colder air from N from around the 27/28th but that air will not be sourced directly from the Arctic (Or of it is not for very long) and so ice days looks unlikely at this point but some, more especially in the N, should see snow falling even if it doesn't stick around. 

As things stand the Atlantic ridge looks like slowly being degraded rather than getting a Greenland high, but not disastrously so since there could well be a renewed attack from the N after a brief milder spell and renewed amplification after any low pushes over the ridge. It is all too far out to do anything but speculate and there are all manner of possibilities some better, some worse.

 

Overall I think we should be happy to have a shot at seeing some snow and the S is not excluded in that by any means even if it isn't a classic Winter pattern for now because it is far better than what we normally get and there is nothing to say the pattern will flatten in the New Year and that blocking will not re-strengthen. That is something to keep tabs on but there is currently no clear signal either way.

In the meanwhile enjoy this 168 mean chart which we would have given our right arms for only two weeks ago.

 

Looking forward to see what this evening brings.

[DanDorsetUK]

35 minutes ago, Kasim Awan said:

When I used the word "zonal" 

 

The first rule of cold club is you do not talk about Zonal. The 2nd rule of cold club is you do not talk about Zonal.

Edited December 20, 2020 by Rapodo

[Cold Winter]

7 minutes ago, northwestsnow said:

Nice Post again.

This is the kind of setup that sees local hills do  well...

I posted earlier, hills across much of Northern England, moreso towards Scotland will,or could see some snowy weather in the coming weeks...

 

You’re right, of course the hills should do well. I’ve noticed the 850s are steadily trending downwards however, and we’re still a long way out...

12z Friday & 6z today for my area below. The mean 850 temp has dropped from around -3 to -5c in the last 48 hours. Could it continue? Maybe.

12z Friday:

 

6z today

Edited December 20, 2020 by Cold Winter

[BlueHedgehog074]

9 minutes ago, northwestsnow said:

Nice Post again.

This is the kind of setup that sees local hills do  well...

I posted earlier, hills across much of Northern England, moreso towards Scotland will,or could see some snowy weather in the coming weeks...

 

Let’s hope we can get some to lower levels too Even if it’s of the falling, rather than settling, kind. Some surprises definitely couldn’t be ruled out anywhere depending how the models continue to handle the weather patterns after Christmas. 

Certainly Christmas itself looking chilly and festive

Edited December 20, 2020 by DiagonalRedLine

[Scandinavian High.]

Well meto seem to be onboard now with severe conditions in the north and south could get snow aswell 

[northwestsnow]

1 minute ago, Scandinavian High. said:

Well meto seem to be onboard now with severe conditions in the north and south could get snow aswell 

Are they?

I've not seen anything, I'll have a look...

Let's hope for upgrades im desperate to wheel out some gifs !!

[Vikos]

Snow charts from ECMWF 00z +144, +168, +192,+240h

   

 

Temps

     

[The4Seasons]

Latest met office outlook now seems to be inline with (models consensus) for the medium term prospects. Highlighting it becoming possibly  stormy with heavy rain or potential snow towards the new year. Looking at the utility industry updates I get its seems like it will be more marginal to higher ground the further south you go and more to the lower levels further north - (north of M4 for example - the better the odds of seeing snow). As is usually the case. Critically it will come down to how low those upper layers reach across the country. Interesting watching to come .