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

[ICE COLD]

9 minutes ago, Kentish Snowman said:

Yep.  The op run looks just about the mildest run of the lot uppers wise for Christmas day.  Lots of ensembles taking a nose dive around Christmas there

Oh I would just love a cold and snowy Christmas week for once . 

@feb1991blizzard that’s 3 runs on the trot the GEFS have got genuine flat lining in

Edited December 10, 2020 by ICE COLD

[Eagle Eye]

Zonal snow maybe meanwhile up North certainly looking possible. 

[Skullzrulerz]

1 hour ago, mb018538 said:

I'm....dreaming....of a mild....Christmas?

At least it will be dry! 

A far cry from what was being shown on the models a day ago 

[chris55]

1 hour ago, West is Best said:

Yes and I see no convincing evidence that an Artic High is any bleeding use for the UK. In fact, iirc, the best scenario is displacement of the polar vortex, not its static placement under a high pressure. An Artic High is zero use if, as seems the case, the jet drives like a coach and horses through the eastern seaboard.

We need a proper Greenland High, or a mid-Atlantic block. At worst case a Svalbard High. Anything else is not sufficient for the UK to have a sustained cold spell.

On very rare occasions it isn’t to bad

[Day 10]

34 minutes ago, Broadmayne blizzard said:

Not on Pert 13 it isn't. That's the minus 15 Cobra run.

Bitter!

[STRiZZY]

2 minutes ago, Day 10 said:

Bitter!

Can we lock this in please? 

[TSNWK]

5 minutes ago, Day 10 said:

Bitter!

Trend setter.. from little acorns.....

[chris55]

34 minutes ago, Day 10 said:

Bitter!

That’s pretty much a re-run of the 87 charts I posted above

[SqueakheartLW]

After looking at the GFS and its members for the first full day of Christmas Day runs these are the totals I got for each option

Temps        9/12          Precip        9/12
V Mild         0                V Dry         1
Mild            13              Dry             36
Average     45              Average     59
Cold           54              Wet             32
V Cold        16              V Wet          0
LEADER     COLD         LEADER      AVERAGE

Overall looking more likely to be colder than milder and there were several very cold options in there and a couple of beast from the east scenarios too. Precipitation overall came out easily average yesterday

Time to see how today's runs are doing so far in terms of colder options for Christmas Day. I have both the 00z and 06z options mixed together in this update and have picked out the coldest options showing in both or the ones that have potential to deliver cold and/or snow too. As always the least cold first and coldest last

GFS 06z Member 21

A rather feeble attempt at an easterly here but at least colder uppers are waiting over the continent but with the positioning of the high pressure it could take a while for them to arrive. More cold with overnight frosts here

GFS 00z Member 20

This is looking like a slidergate battleground situation with a snow threat on the NE side of the low pressure where the mild air clashes with the colder air further N and E

GFS 06z Member 15

A seasonable Christmas Day here with slack winds generally and quite chilly uppers. Frost and fog the most likely elements at play on the surface

GFS 06z Member 28

An area of low pressure here positioned within quite cold uppers. Could be a marginal snow event if things fall right here, especially in the NW closest to the low pressure itself

GFS 00z Member 12

A more significant battleground situation here of 2 types. The first is similar to the other one with mild vs cold clashing over the UK giving a snow event for some but the other main battle here is between that large low pressure area and that huge block over Greenland at 1070mb too. All coldies would want Greenland block to win out and all mildies would want that low to win.

GFS 06z Member 16

Another anticyclonic option but the stronger winds will mean less risk of fog and frost but very likely a cold and cloudy flow here making for a raw feeling Christmas Day

GFS 00z Member 9

A cold and wet Christmas on the cards here for most but the lucky few in the NE of the UK may see a snow event as that small low passes through before no doubt the next low arrives and brings milder air with it for Boxing Day

GFS 00z Member 19

A bit more of a mini battleground situation here between a small low pressure and a small high pressure. Snow is a possibility through the spine of the UK with the west milder and dry, the east colder and dry too

GFS 06z Control Run

This looks like the beginnings of a cold easterly flow but nothing more than -5 uppers in the flow for now. Cold, frosty and maybe a snow shower risk for the SE here

GFS 06z Member 7

Not typical to feature a gentle NW flow but this one is quite chilly for a NW wind and has the potential to deliver some snow to the NW, especially over high ground

GFS 06z Member 4

A colder version of the last option with a bigger snow shower risk in the N. As with this and the last option the S and E staying dry.

GFS 06z Member 3

Anticyclonic option which will deliver cold and frosty weather for Christmas itself but also a bit of a battleground too which all depends on where the high goes to next. Moves north and very cold air is waiting to move across to the UK. South and a very mild airmass is waiting out in the Atlantic to ruin the late December period.

GFS 06z Member 14

A nice option here with that small low delivering what will very likely be increasingly wintry showers to the E as colder air moves in for Christmas Day. Even colder air is waiting in the flow further to the NE and could easily move in as long as the pattern holds.

GFS 06z Member 30

A fairly cold northerly here with a snow shower risk, mostly for the N and E. Not much colder uppers either until you get right into the Arctic and Russia so a long wait for anything even colder here

GFS 00z Member 27

A colder version of the previous marginal low pressure situation and with the low pressure closer than the other option then this could be a more certain bet for snow on Christmas Day

GFS 00z Member 2

A mainly dry and cold option unless you are close to that low where snow showers are likely in the SE and on exposed E coastal regions in England in particular.

GFS 00z Member 14

Finally onto the best options of all. In 3rd coldest we have GFS 00z Member 14. This one is a slack version of a beast from the east with the -10 isotherm just getting into the UK. Very cold here with snow showers mostly in the east. More likely very cold and dry in the S and W with more of a continental influence.

GFS 06z Member 13

An even colder version of the above. Yet again a slack flow, even more so than the previous one. This one may have a snow risk near the east coast but inland areas likely to see ice days and very low minimums at night. The -15 isotherm isn't far away either and could easily move in.

GFS 00z Member 5

Finally the option I think is the best overall for the cold and the direct flow from the east too. This looks like a repeat of 2018 with the uppers and the direction and strength of the wind. The -15 isotherm is just getting into the UK and is likely to push even further into the UK. Frequent and heavy snow showers will be the order of the day and these are likely to get some way inland on this flow too.

Summary

A total of 19 cold or potentially cold options there between both the 00z and 06z GFS of a possible 64 options. Not that bad but a lower fraction overall compared with yesterday's runs but I will have to see what the 12z and 18z bring in terms of cold.

EC ENS z500 latest charts vs same time last year

09/12/2020       12z                  vs             09/12/2019      12z

10/12/2020      00z                   vs           10/12/2019      00z

Summary

I have yet again shown the ENS charts. This is mainly to show that this year we appear to be headed for northern blocking around Christmas. When comparing this year to what the identical runs were showing last year on the same dates there is a big difference. Last year was all about the wet weather and zonality. This year looks much different and gives me more hope of a cold or maybe even white Christmas this year

[feb1991blizzard]

Just a quick one @SqueakheartLW That 2020 chart is only slightly blocked up to the NE, the orange over Greenland is above average heights compared to the climatological norm not compared to the areas around it, so not very very blocked that chart.

 

There's a trough of 510 heights in the Atlantic to the NW.

Edited December 10, 2020 by feb1991blizzard

[mb018538]

Thanks @SqueakheartLW - hell of a lot of work gone into that post!

Please, take note of those ensemble cluster comparisons! Last year was about as zonal as you could get. This year is very different.

We are NOT currently in a zonal spell of weather....it's a blocked pattern. I think people tend to think of blocking as high pressure and dry. Somewhere will be dry and cold, but equally, when there's a block you have to have a stagnant area of of troughing that doesn't move too. We just happen to be under it at the moment, it doesn't mean the weather is zonal!

[mushymanrob]

My reply to @Valleyboy who doesnt think charts are accurate beyond 5 days is this.

The NOAA 500mb anomaly chart created on December 3rd predicting the general pattern of ridging/troughing/mean upper flow for the 8-14 day advance timeframe. The GFS chart is for Saturday 12th.

That illustrates that the anomaly charts are accurate well beyond the 5 day timeframe as the GFS for Saturday is pretty much bang on what was predicted 9 days earlier.  I rest my case.

 

[Updated_Weather]

Anyone explain if this is a negative/positive or no impact for our chances of cold weather?

[PDM]

hello all

Christmas period charts now coming into range but IMO anything over 144hr must be taken with a large pinch of salt! there is a general trend though pointing towards colder conditions but how cold is yet to be seen. surprised that the BBC have indicated possibility of colder end to December and even the Met Office 30 day update signally potentially  very cold nights.(their words not mine) . I'm not a fan of weather Apps but the latest BBC weather App does show a sleet shower on 23rd December and 6c here in North Oxfordshire. all I can see is that its a lot more interesting than this time last year! 

[Eskimo]

19 minutes ago, mushymanrob said:

My reply to @Valleyboy who doesnt think charts are accurate beyond 5 days is this.

The NOAA 500mb anomaly chart created on December 3rd predicting the general pattern of ridging/troughing/mean upper flow for the 8-14 day advance timeframe. The GFS chart is for Saturday 12th.

That illustrates that the anomaly charts are accurate well beyond the 5 day timeframe as the GFS for Saturday is pretty much bang on what was predicted 9 days earlier.  I rest my case.

 

I don't think this proves that charts are accurate, I think it may just prove charts can be accurate at times. It would be interesting to see the verification statistics of the NOAA charts, but I suspect they would be fairly low. 

Edited December 10, 2020 by Eskimo

[Radiating Dendrite]

Just now, Updated_Weather said:

Anyone explain if this is a negative/positive or no impact for our chances of cold weather?

Negative - we need an active MJO.....part of the reason we are struggling to clear troughs through to the east of the UK.

[STRiZZY]

28 minutes ago, SqueakheartLW said:

After looking at the GFS and its members for the first full day of Christmas Day runs these are the totals I got for each option

Temps        9/12          Precip        9/12
V Mild         0                V Dry         1
Mild            13              Dry             36
Average     45              Average     59
Cold           54              Wet             32
V Cold        16              V Wet          0
LEADER     COLD         LEADER      AVERAGE

Overall looking more likely to be colder than milder and there were several very cold options in there and a couple of beast from the east scenarios too. Precipitation overall came out easily average yesterday

Time to see how today's runs are doing so far in terms of colder options for Christmas Day. I have both the 00z and 06z options mixed together in this update and have picked out the coldest options showing in both or the ones that have potential to deliver cold and/or snow too. As always the least cold first and coldest last

GFS 06z Member 21

A rather feeble attempt at an easterly here but at least colder uppers are waiting over the continent but with the positioning of the high pressure it could take a while for them to arrive. More cold with overnight frosts here

GFS 00z Member 20

This is looking like a slidergate battleground situation with a snow threat on the NE side of the low pressure where the mild air clashes with the colder air further N and E

GFS 06z Member 15

A seasonable Christmas Day here with slack winds generally and quite chilly uppers. Frost and fog the most likely elements at play on the surface

GFS 06z Member 28

An area of low pressure here positioned within quite cold uppers. Could be a marginal snow event if things fall right here, especially in the NW closest to the low pressure itself

GFS 00z Member 12

A more significant battleground situation here of 2 types. The first is similar to the other one with mild vs cold clashing over the UK giving a snow event for some but the other main battle here is between that large low pressure area and that huge block over Greenland at 1070mb too. All coldies would want Greenland block to win out and all mildies would want that low to win.

GFS 06z Member 16

Another anticyclonic option but the stronger winds will mean less risk of fog and frost but very likely a cold and cloudy flow here making for a raw feeling Christmas Day

GFS 00z Member 9

A cold and wet Christmas on the cards here for most but the lucky few in the NE of the UK may see a snow event as that small low passes through before no doubt the next low arrives and brings milder air with it for Boxing Day

GFS 00z Member 19

A bit more of a mini battleground situation here between a small low pressure and a small high pressure. Snow is a possibility through the spine of the UK with the west milder and dry, the east colder and dry too

GFS 06z Control Run

This looks like the beginnings of a cold easterly flow but nothing more than -5 uppers in the flow for now. Cold, frosty and maybe a snow shower risk for the SE here

GFS 06z Member 7

Not typical to feature a gentle NW flow but this one is quite chilly for a NW wind and has the potential to deliver some snow to the NW, especially over high ground

GFS 06z Member 4

A colder version of the last option with a bigger snow shower risk in the N. As with this and the last option the S and E staying dry.

GFS 06z Member 3

Anticyclonic option which will deliver cold and frosty weather for Christmas itself but also a bit of a battleground too which all depends on where the high goes to next. Moves north and very cold air is waiting to move across to the UK. South and a very mild airmass is waiting out in the Atlantic to ruin the late December period.

GFS 06z Member 14

A nice option here with that small low delivering what will very likely be increasingly wintry showers to the E as colder air moves in for Christmas Day. Even colder air is waiting in the flow further to the NE and could easily move in as long as the pattern holds.

GFS 06z Member 30

A fairly cold northerly here with a snow shower risk, mostly for the N and E. Not much colder uppers either until you get right into the Arctic and Russia so a long wait for anything even colder here

GFS 00z Member 27

A colder version of the previous marginal low pressure situation and with the low pressure closer than the other option then this could be a more certain bet for snow on Christmas Day

GFS 00z Member 2

A mainly dry and cold option unless you are close to that low where snow showers are likely in the SE and on exposed E coastal regions in England in particular.

GFS 00z Member 14

Finally onto the best options of all. In 3rd coldest we have GFS 00z Member 14. This one is a slack version of a beast from the east with the -10 isotherm just getting into the UK. Very cold here with snow showers mostly in the east. More likely very cold and dry in the S and W with more of a continental influence.

GFS 06z Member 13

An even colder version of the above. Yet again a slack flow, even more so than the previous one. This one may have a snow risk near the east coast but inland areas likely to see ice days and very low minimums at night. The -15 isotherm isn't far away either and could easily move in.

GFS 00z Member 5

Finally the option I think is the best overall for the cold and the direct flow from the east too. This looks like a repeat of 2018 with the uppers and the direction and strength of the wind. The -15 isotherm is just getting into the UK and is likely to push even further into the UK. Frequent and heavy snow showers will be the order of the day and these are likely to get some way inland on this flow too.

Summary

A total of 19 cold or potentially cold options there between both the 00z and 06z GFS of a possible 64 options. Not that bad but a lower fraction overall compared with yesterday's runs but I will have to see what the 12z and 18z bring in terms of cold.

EC ENS z500 latest charts vs same time last year

09/12/2020       12z                  vs             09/12/2019      12z

10/12/2020      00z                   vs           10/12/2019      00z

Summary

I have yet again shown the ENS charts. This is mainly to show that this year we appear to be headed for northern blocking around Christmas. When comparing this year to what the identical runs were showing last year on the same dates there is a big difference. Last year was all about the wet weather and zonality. This year looks much different and gives me more hope of a cold or maybe even white Christmas this year

What a post. Thank you for that effort as it must have taken some time to put together. 

What numbers did yo use to differentiate between mild and very mild/ cold very cold? 

[Geordiesnow]

1 hour ago, chris55 said:

On very rare occasions it isn’t to bad

Oh look at them charts, not a big fat meaningless Russian high in sight, therefore pressure can fall in Scandinavia and cold air flooding southwards and westwards. Classic charts we barely see these days with the main exception of end of Feb 2018.

Its fair to say, we are a long way off seeing charts anywhere near that sort of set up at the moment. 

[mushymanrob]

31 minutes ago, Eskimo said:

I don't think this proves that charts are accurate, I think it may just prove charts can be accurate at times. It would be interesting to see the verification statistics of the NOAA charts, but I suspect they would be fairly low. 

NO chart is accurate all the time, the NOAAs are the most accurate for the 6-14 day timeframe and they are rarely far from wrong.  @johnholmes (60 years experience both pro and amateur) researched this a while ago and found the 6-10 day chart to be 80% (ill let john correct me if im wrong) accurate... now thats a hell of a lot higher then @Valleyboy s 0 % past 5 days ...lol. Which is the point...

[Relativistic]

17 minutes ago, Geordiesnow said:

Oh look at them charts, not a big fat meaningless Russian high in sight, therefore pressure can fall in Scandinavia and cold air flooding southwards and westwards. Classic charts we barely see these days with the main exception of end of Feb 2018.

Its fair to say, we are a long way off seeing charts anywhere near that sort of set up at the moment. 

And why would the Russian high be meaningless?

[Updated_Weather]

ICON 12z rolling out.. Wonder what this will show? 
Then our favourite GFS12z soon after.. 

[Jason M]

21 minutes ago, Relativistic said:

And why would the Russian high be meaningless?

Not sure I would have chosen those words as I guess its not meaningless if you live in Russia . From a UK cold perspective though this is actually a really common influencer on the UK during Autumn / Early Winter. Trouble is that the orientation and positioning tends to leave us in winds from a southerly quarter thereby meaning we can't get any depth of cold. In essence a dominant Russian high often is the precursor of mild weather for NW Europe. You will see interesting looking synoptics on occasion but the cold air at 850 level is always out of reach.

Personally, I think a big cold spell is very unlikely because we will always struggle with the Euro heights and once in place they are very hard to shift but that's just me. I also note the similarity between all the good charts we are seeing, which is that they invariably 15 days away!! 

I tend to view the Russian high as a winter killer rather than a winter giver (especially in early winter). If you want snow the heights need to be centered around Greenland and / or Scandi. A ridge thrown out towards Scandi from The Russian high rarely delivers (albeit it looks pretty on the charts). 

 

Edited December 10, 2020 by Jason M

[swfc]

11 minutes ago, Updated_Weather said:

ICON 12z rolling out.. Wonder what this will show? 
Then our favourite GFS12z soon after.. 

Looks ok tbh

[Ali1977]

Day 8 on the ICON, the PV is smashed to pieces but unfortunately we aren’t profiting from this - yet. I think we are in a good place, small steps to something colder around Xmas Eve. 

[sebastiaan1973]

2 minutes ago, Ali1977 said:

Day 8 on the ICON, the PV is smashed to pieces but unfortunately we aren’t profiting from this - yet. I think we are in a good place, small steps to something colder around Xmas Eve. 

I think -based on the De Bilt plume- we can't expect anything 'good' until the 22th of december.