[Model Output Discussion - moving into Winter]

Came on today expecting there to be some Christmas joy in the forums  and shocked to see so many Debbie Downers!! This is the best chance of cold conditions (and potentially snow) we've had in December for quite some time. 

[Model Output Discussion - moving into Winter]

38 minutes ago, tight isobar said:

If anyone moans or waffles b####x regarding the ec 12z I’m gonna come round and poke ya in the eye 👁...

Ehhh EC could be better.. No -15c 850hpa temps over us!!!! 

[Model Output Discussion - moving into Winter]

Love how we are calling runs that don't show the -5 or -8c isotherm getting into the country 'mild' 

[Met Office and BBC Weekly/Monthly Outlooks]

This may bring some wintry weather, with an increased risk of overnight frost and perhaps snow showers, not confined to higher ground.!!!!

[Autumn 2022 - Moans, Ramps & Chat]

6 minutes ago, Ed Stone said:

Bust or stinker?

Crap or cracker?

[Model Output Discussion - moving into Winter]

30 minutes ago, Ed Stone said:

I'm still not seeing anything all that cold. Yes, possibly cold enough for a touch of snow, but nothing out of the ordinary:

    

Depends what you class as 'ordinary' right now. Normally we'd be mild with wind and rain

[Model Output Discussion - moving into Winter]

This is all very exciting! Definitely getting into the Winter spirit now.  

[Model Output Discussion - moving into Winter]

1 minute ago, Beanz said:

It’s not about whether I’m pleased, I would love to see deep cold setting in, believe me.  I just don’t understand how people are so naive to be claiming something that simply isn’t there…yet.  

When we see those cold uppers coming into the reliable time frame, with a decent pattern in place and more member support, then I’ll be right there with you.  

Until then, it’s just noise. 

I would much prefer the setup we currently have than what we normally have. We just have to be patient.

[Model Output Discussion - moving into Winter]

Just now, Beanz said:

That’s not showing ‘deep cold’ -8/-10, it’s showing a brief period of -5.  

Guess you can't please everyone. 

[Model Output Discussion - moving into Winter]

1 minute ago, Beanz said:

There’s no deep cold showing within a sensible timeframe.  This is T240, so I think the sensible comments still stand - there’s no deep cold.  

The uppers are forecast to be well below average for the foreseeable, with just the odd outlier producing warmer than normal conditions.

[Model Output Discussion - moving into Winter]

Not sure why people are getting hung over on the small details when we have this absolutely smashing update from the Met!

[Model Output Discussion - moving into Winter]

36 minutes ago, DiagonalRedLine said:

While there is no guarantee snow will seize the UK from this blocky pattern (except maybe Northern High ground), the outlook the charts show are not like the below. Far from it:

 

Strong Vortex to our North on our side of the Northern Hemisphere combined with Atlantic, Westerly drivern weather. Worst nightmare for cold weather enthusiasts. Where as, while details will still change at that range, the outlook for beginning of this December below is completely different…

…and is like the

of the charts for the cold and snow fans.

(Just got to pray now that any signs of deeper cold and wintrier weather in the far out range of the models gets down nearer the 0 hour mark, even if it means having to wait. But this is still a big step up compared to what is typically endured during a number of Decembers).

Agreed. The charts being released currently are a far cry from what is usually released at this time of year (an Atlantic dominated scenario). These charts are quite spectacular and the level of blocking that is being produced by some of these runs is just extraordinary. 

[Model Output Discussion - moving into Winter]

4 minutes ago, Mapantz said:

Common charts to look at are the 500-1000hPa thicknesses.

Here's a GFS example at 315 hours.

There are other circumstances whereby looking at the 850-1000 thicknesses are more beneficial.

more info

Thank you for that link! It's very helpful and I now understand the thickness lines a lot better.

[Model Output Discussion - moving into Winter]

Just now, MAF said:

""When the thickness is 5280 m, or 528 dam, then we can expect a polar air mass. If the 528 line is to the north of the UK, then we’re likely to get rain, but if it lies to the south of us (as in the forecast pressure chart above), the chances of snow are much greater. And if you spot the 510 line over the UK – well, best dust off that sledge!"" courtesy of RMS

Thank you very much! So it's sort of like an indication of what type of weather we can expect to be seeing?

[Model Output Discussion - moving into Winter]

What does '528 dam' and '510 dam' mean? I know I saw a post on here a few days ago saying there have only been a few rare instances on when 510 dam has been over the UK (such as the BFTE in 2018), but what does this actually mean?

[Model Output Discussion - moving into Winter]

Just now, Mark wheeler said:

Thanks, this has answered the question I was quietly asking myself, all have been celebrating that run and I was sure it didn't deliver on that chart for us in the southeast . I was a bit tense to ask as thought i was just reading the chart wrong . I need to look at the bigger picture sometimes.

Don't be afraid to ask!! Everyone in this forum is very helpful and polite, it's a proper community here  

[Model Output Discussion - moving into Winter]

Just now, Allseasons-si said:

The mean goes below -5 for the first time,...so an upgrade in that respect

sorry this bit is not MOD related but my OH has just been rushed to Hospital with her conditon deteriorating so i will be limited on here as of now,...sorry

Really sorry to hear that, hope she is okay

[Model Output Discussion - moving into Winter]

1 minute ago, josh-weather said:

Isn't this just a result of chaotic atmosphere Vs attempts at prediction? It can be seen with ensemble runs too, a widening envelope of possibilities into the future, because we can't really predict well out there.

 

Individual op runs can vary just the same, its just that we experience them one at a time and fixate on the very cold ones while binning the very warm ones.

The wildest of weather will always be more likely to show up in the distant reaches of FI, surely. Just because of the mechanics of how this whole thing works.

Meanwhile theres a nice more seasonal spell coming up, further cold in the ensembles and who knows we might get lucky.

Yes I understand that. Very seasonal spell is looking likely to be with us soon , probably not much in the way of snow apart from the high reaches of Scotland to begin with, but we can see how the evolution plays out as there are so many possibilities on the roulette wheel

[Model Output Discussion - moving into Winter]

28 minutes ago, SLEETY said:

The end of gfs has December 1978 vibes about it, amazing run towards the end, bitter cold and snow for most of Europe nevermind just the UK. That depth of cold is rare for Mid-december, actually anytime of winter these days it feels like. 

A long way out and charts rarely verify at that range but if they did be 

Some concern though for the authorities I'm sure the Met are keeping close eye on things at the moment. 

Best charts at this time of year since 2010

I'm just as excited about this potential cold spell as much as the next person, however, isn't it always the real cold is day 10+?

[Model Output Discussion - Deeper into Autumn]

5 minutes ago, Mike Poole said:

Hey, welcome back to the mad house, @nick sussex!  We are in interesting times…

ECM mean at T240 still very clear in the position of the blocking high anomaly, to our north and maybe a bit bi-modal between south Greenland and Scandi:

Looking at the clusters T192-T240, one thing sticks out is how the variance between whatever clusters the algorithm has deemed appropriate at this timescale has reduced in the last couple of days.  Now, the location of the block and even its shape doesn’t vary too much:

It is pretty much all north of the UK, maybe cluster 3 just includes UK, so that firms up the easterly.  Also, the idea of it heading off to Russia seems to be discounted now, it is staying put to our north somewhere.  

T264+:

Here we seem headed to a Greenland block, only difference of whether it is a weak block (cluster 2), strong block (cluster 1) or monster block (cluster 3).

I don't think I have ever seen whites on a cluster map.

[Model Output Discussion - Deeper into Autumn]

39 minutes ago, Singularity said:

My eyebrows have raised this evening as GFS has produced a rare 'bottom-up' stratospheric polar vortex split via a trough splitting against Greenland & ECM has something similar by Greenland on the same day (next Sat)..

As far as I'm aware, this is what happened in late Nov 2010, so it's worth keeping an eye on future runs for any consistency regarding the trough split against Greenland.

 

What does a 'bottom-up' stratospheric polar vortex mean? Sorry for the dumb question.

[Model Output Discussion - Deeper into Autumn]

3 minutes ago, Ali1977 said:

It’s hard not to get too excited baring in mind it’s still quite some time off , but are we on the cusp of something extreme here I wonder extreme as in prolonged Siberian or arctic air and very cold CETs.

The very cold air has just hit the U.K. by day 9 on this run - big lurch forward in time. 
 

We’ve been here before though, I won’t be using the BOOOOMs yet.

Well, we need see a CET of less than -2.2 to not break the all-time highest CET record. Could this be achieved???

[Model Output Discussion - Deeper into Autumn]

1 hour ago, Eagle Eye said:

Agreed

Beware : Quite a long post coming up:

I also think we need to be a bit cautious when we talk about the -NAO as the nailed on 100% cold that its sometimes discussed as.

You've got to give time for the cold pool to develop on the Eastern side of the Greenland high otherwise its essentially useless just might be associated with a brief cold pattern.

Luckily we do have the time on our side as the AAM stays relatively stable and Nino-esque.

The GWO is moving towards a phase where over the next week or so when we'll likely lose Atmospheric frictional torque and the AAM goes down . Beyond that we should enter phases of postive friction torque then southward momentum and circumglobal troughs as the AAM increases again so a brief dip then back to normal. You should also refer that there is still a lag correlation with this (not sure how long it is sorry) so keep that in note.

Note that the forecast is slightly out of date.

What does this all mean though?

The main way to lose or gain Atmospheric Angular Momentum (AAM) is by the imparting of frictional or mountain torque to or from the earth or the oceans.

Frictional torque is the rotational force imparted on the atmosphere by the friction of the surface.

Mountain torque is the torque acted by having different pressure systems on either side of a mountain.

The main way of gaining AAM is by having frictional torque and mountain torque (sort of) move from the surface to the atmosphere imparting eastward momentum into the atmosphere, weakening the relative wind. It is also associated with a Nino-esque AAM when the AAM anomaly is above 0.

What does this do though?

Weakening the relative wind increases the wave oscillations from the tropics and so we get the large scale WAA and blocking perhaps towards Greenland. Greenland blocking is where you get -VE (negative) NAO that has been discussed at length before.

Whereas weakening AAM decreases the oscillations and when the AAM anomaly is below 0 it's Nina-esque. What this does is decrease the strength of oscillating tropical waves and that promotes a +VE (positive) NAO pattern and a flatter and stronger relative wind and so the Atlantic is more dominant.

Positive Friction torque?

Where the friction torque is coming from the earth to the atmosphere and so the AAM increases. 

Why is southwards momentum transport between the equator and 30N seen as a good thing when surely it dampens the wave amplification?

Since a steady state atmosphere is assumed, southwards momentum results in the equal and opposite reaction in the other direction and so there is also northwards momentum transport. Interestingly, the same sort of principal but on a more dynamical basis works in Convective modes (am I getting boring yet ) so I may end up researching into that another time.

What about circumglobal troughs?

Couldn't find much but it sounds like it's talking about where the troughs on the other side are more of a dominant force than the peaks.

So after these next 1 or 2 blocking and therefore -NAO opportunities, mid to late December is also looking interesting based on recent GWO forecasts which can change but I don't think dramatically enough to keep up the interest.

Note that I wrote a lot of this twice after accidentally deleting most of what I'd already written so I may have missed out an important paragraph or two and my brain is starting to hurt so if you do ask questions I may not reply till tomorrow. 

Generally a decent chance of a -NAO, maybe even a few but that doesn't guarantee proper cold but with the time we've got it does increase the chance of proper cold compared to a more rushed pattern than what we have now.

Amazing post  Thank you for your insight. Never knew about friction torque or circumglobal troughs!

[Model Output Discussion - Deeper into Autumn]

12 minutes ago, MATTWOLVES said:

Early look at those ens really does signal a robust build of Heights in the Northern Hemisphere...

I feel its now odds on we go more seasonal with a chance of something more protracted come that mid month period.

And a little word on the vortex...its looking like a punch drunk boxer already and prone to more splits than a bleach blonded hairstyle.

I'm loving these early signs folks...

Yes!! Makes for a very good start to winter and very interesting model watching. Don't think I've been this excited since England won 6-2!

[Model Output Discussion - Deeper into Autumn]

3 minutes ago, Adam lufc said:

I fear a huge back track tonight by the ecm and others. Was really optimistic earlier but thimgs just arent quite clicking are they together rightly.

I hope we dont end up with boring dry cool nothingless december when we had so mych potential.

Don't lose hope. It's not even December yet and the models are already showing great potential for cold and maybe even snow. This blocking scenario is almost nailed on, it's just the position of the high and how that influences our weather to unravel now!