Model Output Discussion - moving into Winter

[SLEETY]

Low further North now, like the Met mentioned could well happen  with milder air getting into the mix with much colder weather further North, where the two air masses meet is where persistent snow could fall. Midlands probably best place, no good further South for the time being typical. 

[Singularity]

To be honest, when I see an 850s mean like this ahead of an approaching south-tracking low, I think 'will the fronts even reach the UK from the south?'.

Funnily enough what the ICON 12z does with the first runner low that most models haven't been developing much (GEM 00z a notable exception) is more or less what I could see the following one doing based on past experience, unless there's one or more breakaway lows to our west Thu/Fri, which is notably not so with the ICON 12z.

(00z ECM on left, 12z ICON on right)

Note how much further south the green shading reaches in the N. Atlantic on the ICON run due to the lack of small lows west of the UK.

This makes it more likely that the next low from the Azores will run into the base of the cold trough by or over the UK, rather than replace it entirely.

A key detail to track across the 12z runs as they roll out.

[Catacol]

3 hours ago, Eagle Eye said:

The differentiation of momentum divided by the differentiation of torque finds us that the rate of change is equal to the cross product of distance from origin timesed by the force. 

So with increasing torque going into the Atmospheric Angular Momentum we see an increasing AAM anomaly which makes sense. Hence the opposite happens with decreasing torque.

So the -VE East Asian Mountain Torque event should drag the GWO towards a -VE Mountain phase which it does, yet, the -VE EAMT seems quite a strong event compared to the loss of AAM being relatively small. This suggests that +VE torque is being applied somewhere else and would help drag the GWO away from the northwards momentum phase as northwards momentum is associated with southwards drag in the Atlantic, flattening the pattern. Instead, it should drag us towards gaining AAM once the -VE EAMT becomes more stable and we see the East Asian wave train engaging with circumglobal troughing.

This could sustain a relatively neutral AAM and our pattern becomes fairly hit and miss. Or it could push the jet to our south, keeping us in a more holding pattern, perhaps leaving room for an increased chance of either Greenland or Scandinavian blocking depending on the state of the AAM feedback and where the highest torque is applied which based off the weekly forecasts alone, I would suggest the strongest torque is associated with torque from the EAMT buckling and colliding with +VE torque along the East Coast of the North American tropics which may favour the longer term Scandinavian blocking but there is also some +VE torque applying itself closer to North America which may have the feedback of holding the Greenland blocking in place.

If you've got a deep -VE torque one side but +VE torque the other side of a continent, then you may just end up with them dampening each other or kt may trigger another event I just simply don't know and my last few paragraphs have been my guesses of the possibilities.

But there is a lot this depends on, it could just end up flattening the pattern, or it could prop up more blocking. I don't think we'll know properly till at least mid December and they'll probably be a lot of flip flopping in the models beyond this potential upcoming cold spell.

We are still in positive AAM territory - just

and mountain torques appear to have bottomed out and are on the way back up

Tendency at 60N has had a significant boost following the significant drop in momentum towards the equator but the Greenland block is going to take up residence at an even higher latitude. 

Tendency would also appear to have bottomed and be on the way back up in any case. 

What does all this mean? Well - be careful first of all to take AAM and associated GWO orbit as gospel. As with anything in the massively complex weather system it is affected by events and it is not a one size fits all solution to forecasting. Chio has highlighted the bottom-up dominance of the block that is setting up and with average westerlies in the lower strat set to weaken we do not have a downwards coupling which is going to blow that block away. In addition, falling momentum given lag is likely to pull the block to the west BUT the same westerly burst at 55/60N - especially if the MJO reconnects - could easily push up another downstream eddy (block/ridge) over Scandy or Eastern Europe. So there is plenty to suggest that an easterly component to the flow is here to stay.

The Vortex is key to all this. Someone posted earlier today that those (like me) who have suggested very cold weather can only come these days as a result of an SSW are about to be proved wrong. Yes - quite possibly looks that way. However, I would qualify this by saying that, although we are not close at the moment to a technical SSW, what we do have is a weakened strat vortex that cannot get a grip of the trop vortex. So - maybe not an SSW but still without that disconnect we would be looking potentially at a block with little longevity. The lesson for me out of all this is to listen and consider carefully something else that Chio stated a day or so ago - namely that a bottom-up split of the TPV and lower SPV by a strong block sat over Greenland is the cold winter jackpot. I think the Feb 2018 top-down split SSW is a similarly potent jackpot but the scenario that is about to occur is certainly potentially special.

My only gripe is that I still feel it is happening a couple of weeks too early in terms of the residual ocean and ground heat that we still have in place....but really I'm being pedantic and overly nitpicky in saying that. Next week could be great - and it may well only be the start of an extended spell in any case. 

[johnholmes]

3 hours ago, Alexis said:

I hope you're not forgetting that winds don't follow isobars exactly

 

hardly having spent 25 years using them!

[Bats32]

GFS 12z

[Snowman.]

Hmm looking too far North for me on the 12z GFS. 
 

Beginning the 12z with a flatter mood this evening. 

Edited December 2, 2022 by Snowman.

[TSNWK]

12GFS going more west and diffused I say at 126 on left 12z  132Z 06Z on right - these early changes set the picture for week 2 as I see it. Not good to see 12Z edge toward ECM  longivity is my view

 

[mountain shadow]

1 minute ago, Snowman. said:

Hmm looking too far North for me on the 12z GFS. 
 

A flat start. 

For you maybe. It's anything but flat.

[Derecho]

1 minute ago, Snowman. said:

Hmm looking too far North for me on the 12z GFS. 
 

A flat start. 

A flat start? 

[Ali1977]

UKMO looks fine to me 

[Snowman.]

1 minute ago, Quicksilver1989 said:

A flat start? 

More in relation to the mood rather than the actual models. 

[Skullzrulerz]

1 minute ago, TSNWK said:

12GFS going more west and diffused I say at 126 on left 12z  132Z 06Z on right - these early changes set the picture for week 2 as I see it. Not good to see 12Z edge toward ECM  longivity is my view

 

Disappointing truth be told, hopefully ECM may backtrack to a more favourable position this evening.

[Mark wheeler]

Ukmo 144

[Lampostwatcher]

Ukmo 12z 

Gfs 12z 

Superb so far ❄🌨🌨

[Met4Cast]

I have no idea why the same people still insist on knee-jerk reactions to very det run. The UKMO is great as is the 12z GFS, just a slight variation on the same theme, the low is just slightly slower to drop south through Scandi.

 

Nothing to complain about here at all.

[Snowman.]

1 minute ago, Lampostwatcher said:

Ukmo 12z 

Gfs 12z 

Superb so far ❄🌨🌨

No snowflakes for your location, at least not yet. 

[TSNWK]

1 minute ago, Mark wheeler said:

Ukmo 144

now to see if the troughs mix out or are enhanched with reloads - could be a frustrating few frames coming up.

[Ali1977]

GFS is still as cold uppers wise as the 06z at T150 - the real cold is nailed on either way 

[danm]

Just now, Met4Cast said:

I have no idea why the same people still insist on knee-jerk reactions to very det run. The UKMO is great as is the 12z GFS, just a slight variation on the same theme, the low is just slightly slower to drop south through Scandi.

 

Nothing to complain about here at all.

 

Agree. I would highly recommend those less experienced to sit back and watch a model run unfold before jumping the gun on knee jerk comments. 

[Vikos]

This will be a nearly NOWCAST thing where the cold outbreak will hit…

[sheikhy]

Well nuttin to complain about from where im sitting!!12zs looks darn good so far!!move to ecm but trough looks to get far enough south for snow!!

[Optimus Prime]

1 minute ago, Vikos said:

This will be a nearly NOWCAST thing where the cold outbreak will hit…

The cold is basically as good as guaranteed. The snow will be a nowcast thing. Multiple times in 2010 heavy snow wasn't really forecast until 2 or 3 days prior. 

[frosty ground]

The orientation of the high is very different allowing more attic air to spill into the Atlantic west of us.

it’s still a cold run but the monster lower out west has a ECM feel to it 

[Singularity]

GFS 12z is similar to today's UKM runs.

Cold air is spread out a bit further west which is not ideal, but no escaping how low the 0°C isotherm and 500-1000 thickness becomes across the UK by late Thu.
Being an Arctic airmass, it's freezing cold until very near the surface where a shallow modified layer (due to North Sea crossing) is the only real resistance to low elevation snowfall. On this particular run I think that would be overcome by anything more than slight precipitation.

For me, it's notable that this is still a long way from the 00z ECM in terms of what goes on to our west.

Also, the strong low near the Azores has been adjusted slightly further west again as of +168, reducing the likelihood of it visiting Europe as an intense feature.

[Chesil View]

4 minutes ago, danm said:

 

Agree. I would highly recommend those less experienced to sit back and watch a model run unfold before jumping the gun on knee jerk comments. 

I,d also suggest looking at the ensembles  before doing so as well.