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

[Allseasons-Si]

@LRD,yes it would be a shame, I am just wondering if the lag effect  from La nina is playing a part with this Atlantic ridge, maybe someone can add to this as it is not my forte

ens and 850's for my local

ECM rolling out now,C'mon ECM

[Tim Bland]

1 minute ago, Mike Poole said:

ECM a tad more amplified, I’d say, let’s see how this one pans out.

Possibly. Prefer GFS in the Greenland region (esp NW) though...

[TSNWK]

But is this MJO but another forecast open to change or not. ?

[Ice Day]

Another improvement on the GEFS, 6z vs 12z (6z first) and the 6z was better versus the 0z.  More members going colder around the Christmas period

   

Things are looking even better further north, these are for the north east of England

Feet on the ground, but these are good signs nonetheless!

[Daniel*]

Looks better towards Greenland.

[Allseasons-Si]

1 minute ago, TSNWK said:

But is this MJO but another forecast open to change or not. ?

Yes,it's certainly changed for the worst since yesterday,but they flip flop just as much as the models do.

[LRD]

2 minutes ago, Daniel* said:

Looks better towards Greenland.

Pretty similar to GFS too

I wouldn't expect too much out of this run, though. The fun and games (if they are to be had) kick in from the 24th

[SqueakheartLW]

After I thought the 06z GFS was a big step in the direction of cold for Christmas Day the 12z has stepped it up even more to my delight and I hope many others on here. The 06z has 15 of 32 members with potential or odds on snow events or cold and frosty anticyclonic options giving a seasonable Christmas at least.

The 12z has upped the colder options even more with a new high of 19 of 32. As before northerlies featured a fair bit again. It was so good this time that I only found 1 option in milder and none in very mild in the 12z

Here are the full 19 options that are either definite snow risk or have potential or are cold and seasonable for the big day

GFS 12z Operational Run

The 3rd GFS run in a row now that the operational run has come out to play white Christmas potential for us again. An Arctic northerly here but with a NW element to it means the N and W most at risk from the snow showers whilst the E and S stay dry and cold

GFS 12z Control Run

Also the 3rd control run in a row to play the cold game. With the two highest resolution runs both showing the theme of northerlies at Christmas this is starting to really increase my hopes of a white Christmas this year. This run features slightly less cold uppers and higher pressure so probably wintry showers in exposed locations but a fair amount of dry and cold weather here

GFS 12z Member 2

I have to admit when I first saw the 500mb chart I expected a bland average 850mb temp. How surprised I was when it turned out to be one of the coldest 12z GFS options in the ensembles for Christmas Day. A risk of snow in the east near that low pressure but dry and cold everywhere else

GFS 12z Member 3

Another northerly variant for Christmas Day here with colder uppers than the other two northerlies featured so far but with the slack pattern more likely to be dry and cold inland with snow showers reserved for exposed N and E coastlines only

GFS 12z Member 4

My first anticyclonic option of the set. Coldest in the east under those colder uppers but less cold in the west. Sun, fog and frost most likely here

GFS 12z Member 7

Not as cold as some options so wintry showers at best but in any heavier ones they should fall as snow. This most likely in the N and W

GFS 12z Member 9

Another northerly here but not very potent compared with some in the ensembles. This one most likely to produce snow in the N and more sleet or cold rain showers further south for the big day

GFS 12z Member 11

This northerly could be a potential snow maker in the east if the precipitation can engage with the cold uppers but most likely snow risk is out west from showers and in the north

GFS 12z Member 12

Generally dry, cold and frosty with this option but the low pressure out west threatens to move in to those cold uppers and could be a real snow maker

GFS 12z Member 16

Another potential snow maker here for Christmas Day and with the colder uppers more widespread than the previous potential option then more odds on for snow here

GFS 12z Member 17

This is a rather cold NW flow for Christmas Day here. Snow showers a real threat in the N especially and even colder uppers waiting to the north if the pattern can hold

GFS 12z Member 18

At first this looked like a real snow maker for my region but I was rather disappointed with the uppers over the UK. At best showers turning increasingly wintry as the colder uppers to the NE move in on the NE flow

GFS 12z Member 20

A transient ridge here for Christmas Day giving seasonable weather at least before the milder air to the west spoils things for Boxing Day

GFS 12z Member 24

Another rather cold NW wind option and better than the other one. This one features overall stronger winds and lower air pressure so a greater snow threat in the N and W and some of this could push further towards the S and E as a result

GFS 12z Member 25

Back to northerlies again and this one is the most potent in the ensembles. Definite snow threat here for the N and E in particular and some decent cold uppers to boot too

GFS 12z Member 26

Back to more anticyclonic again and with cold uppers too then a seasonable day on the cards again

GFS 12z Member 28

A marginal snow threat here for Christmas Day with 2 low pressure areas within quite cold uppers. The low in the south could be cold rain, sleet or snow depending on the exact parameters. The one in the north is a more firm bet for snow with the colder uppers there

GFS 12z Member 29

The most anticyclonic and least cold NW wind option. Seasonable day with frost and fog for Christmas and a small risk of coastal wintry showers in the NW in particular

GFS 12z Member 30

Cold and seasonable Christmas for us but one of those frustrating situations where the core of the cold blast is too far east for our benefit and sends the coldest air into mainland Europe instead. We just end up with persistent high pressure to the end of this run with inversion cold

Summary

A decent run for cold fans with those 19 of 32 colder options showing up. How will the 18z compare before tomorrow I can start to look at other models too that come into the 10 day range

[Dancerwithwings]

19 minutes ago, Tim Bland said:

By Xmas Day evening GEFS are down to -4.5c uppers as an average in the south! Here is the full list

I’m liking that, with 30 pert’s it’s hard to see what’s what at times, that makes it totally clear  you got the direct link please

[Daniel*]

Certainly convincingly better ridging in Atlantic at day 8 those heights to S/SW are annoying though.

[Allseasons-Si]

The ECM is very similar to the UKMO at 144 with regards to the shortwave off the ESB and is a better run in that respect than this morning.

 

[Methuselah]

4 minutes ago, Stevie B said:

So does the MJO drive the ensembles or do the ensembles drive the MJO or do they independently read the background signals?
 

Sorry LRD not directed at you personally just interested. 

I don't think so, Stevie... I suspect it's combination of many things (of which the MJO is merely one?): sea-ice disappearance and the expansion of the semi-tropical zones also come to mind?

IMO, the best information, regarding the current state of the atmosphere, comes from @Tamara... Without a diagnosis, one cannae hope to attempt a prognosis?

[TSNWK]

[TSNWK]

Just now, TSNWK said:

I actually think ECM at 192 is better than GFS for those forming heights to our north west ? 

[Eagle Eye]

Wow what a run. 

 

[A Frayed Knot]

1 minute ago, TSNWK said:

And? Ain't got a clue just like the rest of us trying to learn

[Tim Bland]

I wouldn’t panic too much about the MJO folks. It’s unlikely every model is getting it wrong!

[Kentish Snowman in Yorks]

11 minutes ago, Ice Day said:

Another improvement on the GEFS, 6z vs 12z (6z first) and the 6z was better versus the 0z.  More members going colder around the Christmas period

   

Things are looking even better further north, these are for the north east of England

Feet on the ground, but these are good signs nonetheless!

Hi do you have a link to the charts in this format?  TIA

[Allseasons-Si]

ECM much improved at 192,could see a runner into the south on day ten...

Edited December 13, 2020 by Allseasons-si

[LRD]

1 minute ago, Tim Bland said:

I wouldn’t panic too much about the MJO folks. It’s unlikely every model is getting it wrong!

Yep it's something to consider but no point panicking about it. The Met Office are continuing to talked about low confidence and mixed signals. I guess it's better than last winter when we were facing a polar vortex on speed. We do have a chance of something wintry this time round

[BARRY]

1 minute ago, Allseasons-si said:

ECM much improved at 192,could see a runner into the south on the next frame...

Much better than last week, looks like we may see some cold fingers crossed.

[northwestsnow]

850 profile by day 9 suggest 12z det is significantly colder than the 00z det...

[LRD]

Good trends on the ECM. This morning's run:

This evening's:

Everything much further south. Atlantic looking far more amplified

[That ECM]

2 minutes ago, BARRY said:

Much better than last week, looks like we may see some cold fingers crossed.

Here’s some “cold fingers crossed”

[Scott Ingham]

5 minutes ago, northwestsnow said:

Oww thats not good news at all, in view of us needing as much amplification in the Atlantic as possible.

Don't be too despondent. I'll explain why.

Current State?

We have a northern latitude set up and ongoing weakening of polar winds that are absolutely wipe for northern blocking to take hold due to ongoing weakening of the vortex caused by wave 1 and wave 2 activity the past 4 weeks.

What do we need to take advantage?

Amplification

How do we create amplification?

By creating a rise in angular momentum (AAM)

What can increase angular momentum?

MJO - Tropical convection that moves east into areas of the globe known as the western pacific and central pacific (these are phases 6 7 and 8. Initial forecasts were for a move into 6 and 7 low amp 8 then dieing. Current forecasts show this struggling to get going into 6 which affects its move into 7. Since November this has been under forecast until nearer to time. So no need to worry just yet. Its the NINA we are currently in thats counter acting this. We obviously have cooler waters in the pacific at the minute.

Torque events - This is the current wild card. We have a moderate event an East Asian Mountain Torque (+EAMT) happening right now peaking next Monday or Tuesday as high pressure moves over the Himalayas pushing east into Asia. We also have a forecasted MUCH stronger event due around Christmas time.

What happens if both the convective rain moved east (MJO phases 5 6 and 7) at the same time as the forcing from the torque events? 

We get a rise in AAM (angular momentum) from a base state that isn't that low to start with its just a little above neutral.

What happens if AAM rises?

We get our amplification. Remember the polar field is susceptible right now. Zonal winds are dropping like stones and we have an arctic high waiting for a ridge to come join it from the south to create a winter dance. 

I know the MJO is showing signs of dieing before it gets going but this isn't a certainty the models keep getting it wrong and underestimating it and we have 2 moderate and another strong event almost in the bag.

This year if might not even matter if the MJO runs out or poof and we just have the torque events as the polar atmosphere is so susceptible from the polar high and strat weakening from novembers wave attacks.

Hope this is in enough layman's terms for everyone to understand