Model Output Discussion - Into 2024

[Malarky]

2 minutes ago, Ali1977 said:

With all the amazing charts of the day, this one is up there - ENS clearly having a quicker transition to the cold - by this time tomorrow we should really start having a good idea of the initial transition to cold for Sunday/Monday - hopefully we can really stay sub -6c uppers (snow conducive) for at least a week from then.  

It’d be lovely to see the Op move towards those quicker solutions over the course of the next few runs.

[stodge]

Evening all

A mixed bag of 12Z output as you might expect with an eternity until next week.

Hopes of a clean retrogression of the UK HP to Greenland have been dashed ans we have to "wait" for a final LP to pass between Greenland and Iceland before we can get som traction and that runs the risk of pushing heights south east rather than north west.

That said, on most of the models (JMA looks the exception) we sort of get there in the end and the fun and games begins as the trough drops from Scandinavia towards the British Isles as Atlantic LP approach from the south west. As I've said here before, the key is for the N'ly to be sufficiently robust to force Atlantic LP to elongate and disrupt along the Channel. It's frighteningly fine margins as others have said. 

For the south, it's enormous risk and reward - the risk is the cold airflow hangs too much to the north but the reward is if it's doesn't...

For the north of the British Isles, the certainty of cold is much greater - that may be counted by a paucity of snow (again for some). 

This is all detail which probably won't be firmed up until Thursday.

As for longevity and severity, we often see an almost default "bring back the Atlantic" and the currently moribund jet seems to be fired up presumably by colder air over the north east of North America (this is evident on the GFS 12Z OP but ECM 12Z OP keeps the storms spinning back north west over Canada). It's upstream to which I think we have to look.

The crucial difference is GFS spins a low out of Newfoundland into the Atlantic at T+240 and brings the whole PV (or rather what's left of it) over to Canada/Greenland (response to a Siberian Wave 1 warming?). ECM at T+240 keeps the North American lobe of the PV well over Canada keeping heights over Greenland and maintaining the N'ly over North-West Europe.

Lots of uncertainty into next week but it wouldn't be fun if every chart was identical at T+288, would it?

[jamesthemonkeh]

I always look at the models before coming here to check the reaction, and I was expecting a proper toys out of pram evening in here...yet everyone seems very excited.  Hmmm.

To my eyes, there seems to be more forcing of the low pressure to the south-west, and more of a push of relative warmth into Iberia, on the 12Z tonight:

 

Am I misreading?  Hmmm.

It looks to me that though the chance of battleground snow over England has increased, also the risk of rain and relatively milder conditions has increased too.

If I was a fan of cold, I'd be more wary this evening.  That said, I am a fan of heavy snow, so maybe I'll join in and be excited too...but memories of December 2022 and how that definite/probable/possible/not-happening snow event was modelled make me too cautious for this, right now.

[terrier]

Wow just catching up after a 12hr shift at work. What a great ECM this evening delivers for all. Can see many getting in on the snow shower activity next week lots of disturbances in that set up shown by the ecm. Bring it on ️

[Duane S.]

It would be nice to see this being somewhere near accurate as well. Certainly has support in the early stages of progression 

 

[bluearmy]

13 minutes ago, Scott Ingham said:

Quick question Blue as the Strat is an area I struggle with. Why do you think we’ll see reversal waves for the next 6 weeks after these current round of warmings? Just trying to improve my knowledge 

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so.  Say two waves - three weeks from now and six weeks from now (that’s very approximate) 

[stodge]

2 minutes ago, jamesthemonkeh said:

I always look at the models before coming here to check the reaction, and I was expecting a proper toys out of pram evening in here...yet everyone seems very excited.  Hmmm.

To my eyes, there seems to be more forcing of the low pressure to the south-west, and more of a push of relative warmth into Iberia, on the 12Z tonight:

 

Am I misreading?  Hmmm.

It looks to me that though the chance of battleground snow over England has increased, also the risk of rain and relatively milder conditions has increased too.

If I was a fan of cold, I'd be more wary this evening.  That said, I am a fan of heavy snow, so maybe I'll join in and be excited too...but memories of December 2022 and how that definite/probable/possible/not-happening snow event was modelled make me too cautious for this, right now.

That's the point, though.

Most snow events in southern Britain are very marginal - we talk with awe about December 2010 but that was incredibly rare. The snowfall of February 1st 2009 was just as plentiful in my part of London but very marginal - on that occasion we were on the right side but you know the great big snow flakes tell you it's marginal. 

The evolutions being put forward by the models currently emphasise that risk and reward. That can even extend to rain at sea level and snow at 100m (November 2009). As to whether (so to speak) we will be on the right or the wrong side of the snowline I honestly don't know but for me the most favourable synoptic for southern snow remains the elongating and disrupting Channel LP bumping up against entrenched cold air - that could happen, the line might equally be over the Midlands or even northern France. 

[Scott Ingham]

8 minutes ago, bluearmy said:

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so.  Say two waves - three weeks from now and six weeks from now (that’s very approximate) 

Thanks for the advice appreciated!

[Garthvader]

1 hour ago, Met4Cast said:

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. 

Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. 

Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time.

In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult).

In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. 

Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

Great post ....thankyou 

[terrier]

Right strap yourself in folks almost time for the icon & gfs pub run special. Can see polar bears running down the M4 tonight on the pub run

[Allseasons-Si]

19 minutes ago, Duane S. said:

It would be nice to see this being somewhere near accurate as well. Certainly has support in the early stages of progression 

 

Just a quick one whilst Man utd are at half time

this is good going forward to get us out of a quick unfavourable position to race round to more of a favourable position

latest CPC however kepping in with the blocking theme to our NW,i am still happy with that

[Jason M]

Just now, terrier said:

Right strap yourself in folks almost time for the icon & gfs pub run special. Can see polar bears running down the M4 tonight on the pub run

If so, they will be running along the east bound carriageway because it never snows south of the central reservation 

[Battleground Snow]

Can see the difference in the icon ukmo and ecm v the gfs in the Atlantic.

The low in the Atlantic gets boxed in, while on the gfs it escapes out.

Blocking is more robust when it's kept blocked in 

[Biggin]

29 minutes ago, jamesthemonkeh said:

I always look at the models before coming here to check the reaction, and I was expecting a proper toys out of pram evening in here...yet everyone seems very excited.  Hmmm.

To my eyes, there seems to be more forcing of the low pressure to the south-west, and more of a push of relative warmth into Iberia, on the 12Z tonight:

 

Am I misreading?  Hmmm.

It looks to me that though the chance of battleground snow over England has increased, also the risk of rain and relatively milder conditions has increased too.

If I was a fan of cold, I'd be more wary this evening.  That said, I am a fan of heavy snow, so maybe I'll join in and be excited too...but memories of December 2022 and how that definite/probable/possible/not-happening snow event was modelled make me too cautious for this, right now.

Yep. you are.

[sebastiaan1973]

29 minutes ago, bluearmy said:

As I understand it (and @lorenzo is the go to person here in the strat), reversals in the upper strat generate several repeating waves over the following period up to a couple months. Because the current reversals are downwelling quickly, I would think it’s possible that the waves that follow will only repeat out to six weeks or so.  Say two waves - three weeks from now and six weeks from now (that’s very approximate) 

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

[Day_9]

1 hour ago, Chesil View said:

Let it snow and frosty ground make very good points,when looking at some of our biggest snow events. You often actually need those milder( but still cold uppers) to bring the snow fall.

I hark back to it often but the great South west blizzard of Feb 1978 came with uppers around minus 2 and produced drifts over 20 feet deep.

I got photos of me helping my old man dig his Hilman Imp out of the snow - don’t know why we even tried, the wall of snow from our drive onto the road was almost level with the roof of the house

Edited January 8 by Day_9
Spelling

[sebastiaan1973]

1 hour ago, Met4Cast said:

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. 

Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. 

Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time.

In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult).

In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. 

Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

To me it seems, this in line with EC46 of this night. 

[Scott Ingham]

3 minutes ago, sebastiaan1973 said:

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

Very interesting many thanks Seb!

[Firefly2005]

Just now, Day_9 said:

I got photos of my helping my old man dig his hilman imp out of the snow - don’t know why, the wall of snow from our drive onto the road was almost level with the roof of the house

I know it’s slightly off topic… but still I liked this image and thought I’d respond with photos of our house in the 70s

[sheikhy]

Icon lining up a direct hit at 120 hours!!!!!

[sebastiaan1973]

3 minutes ago, Scott Ingham said:

Very interesting many thanks Seb!

https://wcd.copernicus.org/preprints/wcd-2019-16/wcd-2019-16.pdf 

Thank you and the others for sharing their knowledge. 

[Mcconnor8]

9 minutes ago, sheikhy said:

Icon lining up a direct hit at 120 hours!!!!!

Yep, better Greenland heights than the 12z and therefore alignment of the cold front.

Would be nice to get similar from the GFS, the 12z was quite different to this 18z ICON run so could expect an upgrade.

Edited January 8 by Mcconnor8

[bluearmy]

5 minutes ago, sebastiaan1973 said:

https://wcd.copernicus.org/preprints/wcd-2019-16/wcd-2019-16.pdf 

Thank you and the others for sharing their knowledge. 

 

13 minutes ago, sebastiaan1973 said:

I'm not Lorenzo either, but I think you have to watch the work of Domeisen. In this chart you see the downwelling divided in 4 regimes. Right now we have blocking. This means there will be 2 significant downwellings after this one. This doesn't mean winter at the British Isles or at home in the Netherlands, but increased chance of negative AO.

Does a reversal which doesn’t make it down to 10hpa or 60N count though re onset ?  I mean we saw a reversal beginning 2 Jan which has continued to affect the strat above 70N and will do so until we probably see it get down to 60N in approx 9 days time. Then it will likely relax and we’ll go positive throughout the upper strat.   So does the onset count at 2 Jan?  surely it isn’t when it goes technical in 9 days time ? . 

[Andy8472]

Latest NOAA Blog

https://www.climate.gov/news-features/blogs/polar-vortex/cooking-stratospheric-polar-vortex-disruption

[bluearmy]

 

15 minutes ago, sheikhy said:

Icon lining up a direct hit at 120 hours!!!!!

Is that a shortwave just south of Iceland ?