Model Output Discussion - Colder spell ending, what's to follow?

[cheshire snow]

Wow a GFS that runs 4 times a day a bad run and out comes the doom and Gloom.

@johnholmeshas often said to stick to one GFS run a day and follow that run,personally I follow the GFS 12z to look for trends even if the 06z shows a winter Wonderland i still stick to the 12z.Will say though until Meto come on board I'm not convinced of anything mild or cold.

C.S

@Tamara thank you

Edited December 9, 2020 by cheshire snow

[ITSY]

 

3 minutes ago, cheshire snow said:

Wow a GFS that runs 4 times a day a bad run and out comes the doom and Gloom.

@johnholmeshas often said to stick to one GFS run a day and follow that run,personally I follow the GFS 12z to look for trends even if the 06z shows a winter Wonderland i still stick to the 12z.Will say though until Meto come on board I'm not convinced of anything mild or cold.

C.S

Indeed, crazy responses in here over one run - it's December 9th everyone, cheer up. We're looking for trends for 2+ weeks time guys, I'm not sure how anyone has reached any other kind of conclusion? For those interested, here's some ensembles at t+228 from the 06z. See you tonight

 

[SqueakheartLW]

Now I am back up to date again with my GFS runs and ensembles check again. This time I have finally got charts that say 25/12/2020 on the date so the real countdown can now begin. As before the least cold chart is first through to what looks to be the coldest option

GFS 00z Member 20

The least cold option in the 00z suite. Quite mild uppers but with the high pressure and the general continental feed then this one could contain some surface cold at least with frost and fog possible for Christmas Day

GFS 00z Member 22

A potential snow maker here with option 2. Quite cold uppers contained within that low pressure heading in from off the Atlantic. If parameters fall favourably then that could make for a snowy second half of Christmas Day. At the same time it could just end up cold rain instead.

GFS 00z Member 16

A what looks like a brief blast of cold from the Arctic here no doubt so perfectly timed to deliver a snow threat to northern areas at least. Further south more likely to be just cold and dry, especially when the high pressure moves in later in the day

GFS 00z Member 4

A cold and dry option here with quite sharp frosts by night and cold days, especially in England and Wales. N Ireland and Scotland under a less cold flow circulating around the high so maybe more cloud in these areas and milder temperatures. Potential for much colder conditions if the high can shift north with that cold pool over the continent.

GFS 00z Member 19

Another anticyclonic option. This one has the cold more widespread over the UK but has far less of a cold pool over the continent than the previous one. Probably overall colder over the UK itself but at best a cold and frosty option with no snow

GFS 00z Control Run

The final fully anticyclonic option and probably the coldest of them with us right under the centre of the high pressure region. This means very cold nights, cold days and probably freezing fog a real threat for Christmas Day here

GFS 00z Member 25

Another variant of the Arctic blast option but more of a NW wind here. This means the snow threat is most likely in the N and W. This looks like a Christmas 2004 repeat if this chart plays out

GFS 00z Member 12

A battleground Christmas Day chart here with all that cold air sitting in the east and the mild air trying to push in from the west. Whoever ends up in the boundary between the two air masses will no doubt see a snow even and with high pressure sitting just to the east then this is likely to see the cold air fighting off the mild air

GFS 00z Member 9

Although this northerly doesn't come from that far north a lot of cold air is contained within it and this appears to be quite a snow shower maker option, especially for the N and E of the UK. It looks like that high will develop over Scandinavia and will draw down the colder uppers from the north of it and will then pull these into the UK.

GFS 00z Member 7

A very cold option here with the -10 isotherm threatening the east of the UK. Generally a dry option in the north but the S and E could see a few snow showers from this setup

GFS 00z Member 21

Finally the coldest option with a snow threat in the north in particular. A what looks like will be quite a potent Arctic blast if the high pressure can hold off that next low to the west

EC - ENS z500 00z charts for Christmas Eve

This one needs little explaining since it appears all 51 members are going for northern blocking on Christmas Eve. Quite a decent start then if you at least want a colder Christmas chance.

Summary

A decent GFS 00z update with 11 colder options, now the new highest total so far out of a possible 32 so overall still heading slowly in the right direction if you want cold, frost or snow at Christmas and with the ECM members all going for northern blocking by Christmas Eve then it seems that it is on board with the cold and blocked idea too

[Drifter]

41 minutes ago, northwestsnow said:

We need to see a  turnaround in the modelling over the next couple of days because Dec,or certainly the next 10 days to 2 weeks,  is beginning to look both a washout and a write off for coldies...

All we need is a slight ridge between Atlantic lows in the day 6/7 range and we’re laughing. 
Not much to ask for is it? 

[nick sussex]

Arctic High = Drama 

As soon as that appears the emotional rollercoaster for coldies begins !

There are often modeling problems due to the lack of observational data in that region . The issue at present is how much if any trough disruption occurs near the UK which is connected with how much pressure is exerted on that by the Arctic high and how far sw that ridges .

[TSNWK]

14 minutes ago, ITSY said:

 

Indeed, crazy responses in here over one run - it's December 9th everyone, cheer up. We're looking for trends for 2+ weeks time guys, I'm not sure how anyone has reached any other kind of conclusion? For those interested, here's some ensembles at t+228 from the 06z. See you tonight

 

Nice work there itsy enough scope in the mid term there along with mean to draw me into having a peep at the 12z

And no 22 please if you're offering GFS.  Seriously though there is a huge spread showing at not out in Lala land..

[mountain shadow]

19 minutes ago, SqueakheartLW said:

 

EC - ENS z500 00z charts for Christmas Eve

This one needs little explaining since it appears all 51 members are going for northern blocking on Christmas Eve. Quite a decent start then if you at least want a colder Christmas chance.

Summary

A decent GFS 00z update with 11 colder options, now the new highest total so far out of a possible 32 so overall still heading slowly in the right direction if you want cold, frost or snow at Christmas and with the ECM members all going for northern blocking by Christmas Eve then it seems that it is on board with the cold and blocked idea too

I think it was Bluearmy who said that if you have a single option then it actually means the ENS are not that useful as a guide.

[Penicuikblizzard]

1 hour ago, Portsmouth Sun said:

Unfortunately lots on here do not like reading the truth and believe a D10 when its showing cold.  Reality is a lot different.  

The run up to Christmas looks like a standard mild cloudy/rainy spell with winds from a milder direction.

Quite normal for December being mild and wet to be fair 

[Eagle Eye]

Ready for the greatest run of your lives

9.58

Now ready for the GFS

[PiscesStar]

1 hour ago, cheshire snow said:

Wow a GFS that runs 4 times a day a bad run and out comes the doom and Gloom.

@johnholmeshas often said to stick to one GFS run a day and follow that run,personally I follow the GFS 12z to look for trends even if the 06z shows a winter Wonderland i still stick to the 12z.Will say though until Meto come on board I'm not convinced of anything mild or cold.

C.S

@Tamara thank you

Do you fund the 12z to be more reliable of the four tuns and why? 

[feb1991blizzard]

2 minutes ago, Snowfish2 said:

Do you fund the 12z to be more reliable of the four tuns and why? 

Its the US government that funds the 12z GFS.

[Eagle Eye]

These charst are depressing, I'll be back next year for 2 more flakes of Snow. 

[Relativistic]

26 minutes ago, XanderP007 said:

Ready for the greatest run of your lives

9.58

Now ready for the GFS

To all the confused reactions, I think the 9.58 is a reference to Usain Bolt.

[lassie23]

1 hour ago, General Cluster said:

Deary, deary, me... Is that the plaintive cries of a front-loaded winter writhing on the backburner, I hear?

    

Not the greatest of runs, the 06Z!

The dreaded OFI is coming into play, looks like we may have to wait until Smarch

[syed2878]

1 hour ago, northwestsnow said:

Its possible,personally I think 3 to 4 weeks is stretching it.

There are many background factors at play which could have big knock on effects just prior to Christmas.

 

 indeed there are many background factors and signals at play here nws if I remember rightly winter 2018 2019 had those background signals and where did that get us nowhere really just a standard UK winter living on the Atlantic.  

[syed2878]

2 hours ago, Tamara said:

That was the essence of the post and the numerous inane confused emoticons  were really not necessary.  The alleged techno-babble simply refers to processes that are  highly relevant all times of the year, and do not suddenly only have relevance in winter, which is an impression one can get from reading quite a few posts on this thread between November and March.  That is why I questioned the assertion that it is just a question of waiting for the MJO signal to propagate eastward again in the next cycle at some kind of linear amplitude and progression - because it is not as simple or true as that based on the known recurrence timelines of more active intra-seasonal activity.

The relocation of the tropical low frequency standing wave that has been underway of late from Africa and the Indian Ocean eastward to the Maritime Continent, as was attempted to mention yesterday, is depicted here

 

The importance of this is how much it re-configures the downstream pattern in terms of rossby wave re-alignment. In simple terms, this refers to the placement of the wavelength that amplification of the jet stream takes place c/o of torque processes which change the speed and direction of wind-flow and impact the jet stream.  Furthermore, how active, and how far east, the high frequency MJO (or 'mini ENSO cycle') further interferes during the winter with the walker cell circulation and impacts the tropospheric/.stratospheric pattern. With a w/QBO prevalent through the winter there will be particular reliance of tropical activity to propagate wave eddies poleward via the extra tropics and mountain torque processes to alter the tendency for the seasonal vortex to, otherwise, intensify under a w/QBO regime

Tropical forcing standing wave not progressing further east of the Maritimes (and absence of superimposed high frequency MJO forcing) will restrict convergence of wind-flow further upstream and hence the rossby wave feedback will tend to amplify the Pacific due to suppression of convection and enhanced easterly trade winds in this region. Due to the laws of conservation of angular momentum, there will be compensating extra westerly polar jet inertia heading downstream and restricting the amplification of the pattern here. In this way assisting organisation of the polar vortex gyre.

 

It is clear that the La Nina signal has not defied expectations and has consolidated over time

 

 

However the a-typical relationship that global wind-flows have taken to this Nina-ish base state is much closely aligned to a more Nino-like feedback. Global total angular momentum levels continue to track close to or even slightly above average

The impact of the intra-seasonal high frequency signal very much in play here. However, as per the gist of this and the other post, it will require the tropics to keep alight in order to sustain the present downstream amplification. Inactive MJO activity would lead to angular momentum collapsing and very much more closely matching the Nina-esque base state. This means a much more traditional and flatter pattern and greater influence of the Azores ridge and polar jet flowing around the northern perimeter of the ridge.

At present, there is uncertainty how this might develop in the coming few months. That is why there were very hedged suggestions yesterday - because if one wants to be neutral in assessment and has no particular vested interest in seeing a favoured solution play out, this seems to be (to me at least) an honest position.

 

  would I be wrong in thinking that we are descending into a easterly Qbo after the Phalia?

[IDO]

The gfs op on the 06z was on the warm size and probably in outlier territory:

2m temps 06z London>>

Lots of scatter so no consensus just yet. Looking at the ens individually and over 33% offer something interesting at d8-9 and similar at d12-13, so potential there and looking like any cold (if we are lucky) will be more than a one-day toppler. Some of those 33% get cold quicker, and some slow-burners. A cluster supporting the op (and Control), so worth seeing if the high-res runs are leading the direction or just gfs bias as to lower heights?

[Wildswimmer Pete]

This was Christmas 1957, I remember it well, 57F and sunny (we used old money back then).

[bluearmy]

1 hour ago, mountain shadow said:

I think it was Bluearmy who said that if you have a single option then it actually means the ENS are not that useful as a guide.

Indeed - a quick look at the Iceland meteogram reveals whilst the 80% is quite a narrow spread considering the timeframe, there is a big spread up and down in the remaining 20%. One cluster is going to be a pretty wide envelope ! 

Edited December 9, 2020 by bluearmy

[Daniel*]

-NAO trend is good compare with 2 days ago from EPS an earlier shift as well.

Edited December 9, 2020 by Daniel*

[Radiating Dendrite]

3 minutes ago, Daniel* said:

-NAO trend is good compare with 2 days ago from EPS an earlier shift as well.

Presumably we could have a trough sat directly over us and high pressure to the north / west and get a - NAO?

[Alexis]

Which berk said we needed to get rid of the Russian High? 

[Daniel*]

1 minute ago, Radiating Dendrite said:

Presumably we could have a trough sat directly over us and high pressure to the north / west and get a - NAO?

Yeah but you would expect the stronger the -NAO the more likely the low pressure will be to our south. I get impression we could start rather wet then going drier and colder? 

[alexisj9]

8 minutes ago, Alexis said:

Which berk said we needed to get rid of the Russian High? 

Not me. I thought everything was looking fine, still perhaps this change will lead somewhere later. If only the lows would head SE instead of getting stuck over us.

[mushymanrob]

26 minutes ago, Alexis said:

Which berk said we needed to get rid of the Russian High? 

if that ural block had gone, we would be into easterlies, as pressure is higher to our north. the high to our east is preventing the westward progression of the atlantic energy, and has blocked any deep cold pooling into europe.

the problem with that russian/ural block is the ridging to its southern flank.