Model Output Discussion - Deeper into Autumn

[That ECM]

For any newbies, when we get “good” output we look for how it can go wrong. When we have “rubbish” output we look for how it could flip to good.  
 

 

 

[WINTRY WALES]

2 minutes ago, BLAST FROM THE PAST said:

Valid point, and could be a reason for chilly/raw weather rather than full cold wintry blast.  But still would be conducive to further shots down the line.

 

 BFTP

Hi Blast

Not had one of your great wintry forecast posts for a while…you not expecting much from the model output analysis?? Or trying not to jinx anything

[damianslaw]

19 minutes ago, BLAST FROM THE PAST said:

The deep and extensive cold pooling in Siberia will encourage the large blocking state.   That block will likely be a player to interact with throughout the approaching winter.  I for one see this general blocking pattern lasting through December as a general theme, early view from me coldest week is the last week of December, but could see a decent cold thrust into the second week too.

ECM looks very plausible, as do other model’s blocked theme.  I think we are standing on ever steadying ground with the ESE/easterly awaiting…..but how cold, I think raw to start rather than anything more.  That’ll do me nicely to begin.

 

BFTP

Dec 95 vibes, the second week was cold, then we had a brief respite run up to christmas bit of a toy between atlantic and arctic air, then the last week was the coldest of the month.. it arrived just in time for christmas

[Cheshire Freeze]

3 minutes ago, damianslaw said:

Dec 95 vibes, the second week was cold, then we had a brief respite run up to christmas bit of a toy between atlantic and arctic air, then the last week was the coldest of the month.. it arrived just in time for christmas

'95 is really the first Christmas I can remember for its weather.

I vividly remember several inches of snow being on the ground around that festive week.

[joggs]

29 minutes ago, stodge said:

Evening all

The issue for me is how much strength will remain in the northern arm of the jet - ideally, as per GFS Parallel and a few others, it will be so weak as to be unable to prevent the HP building through Scandinavia towards Iceland/Greenland.

That's more an early May than an early December chart in terms of where the Atlantic trough is and the jet being more or less moribund.

Some other models keep that little bit of energy in the jet such that HLB becomes MLB - GFS OP being a good example. Indeed, GFS toys with what ECM did last night - pushing the trough almost to Iceland and keeping the HLB evolution from happening as we would like.

The jet holds the HP further south closer to the British Isles.

That's the evolution to follow in the next week or so.

Yes,more often than not,the strength of the northern arm of the jet scuppers coldie plans. Tbh I'm expecting that to be the case over the next few weeks. We'll see.

[Cheshire Freeze]

On November 1995 and its relevance to now...you can see, just like now, there were warning signs of what was to come

November is often the month that gives you clues as to how the first part of winter may pan out.

Edited November 24, 2022 by CreweCold

[Polar Maritime]

Just want to add this in for interest by weather history... Re-the current model patern as Crew points out above.

https://community.netweather.tv/topic/34001-the-winter-of-1995-96/

[Cambrian]

ECM ensemble mean at day 15, comparing the 0z and 12z runs, firming up on the eventual Scandinavia - Greenland transfer of high pressure. At this stage, the precise timing probably matters less, it’s the overall pattern and trend between runs that is of great interest. 0z at 360h / 12z at 348h.

 

The amplification of heights into Greenland more profound on the 12z run, with more definite troughing westward into Scandinavia from a deliciously elongated and pointedly directed Asian PV. The Greenland pressure is up from 1020 to 1025mb too, impressive change in the mean at that range. Notice the better pinch between the Greenland and Alaskan ridges too, looking more favourable for a split. Enthralling.

So maybe we get a week or more of progressively colder continental flow before the real Arctic air arrives! 

[Uncertainty]

Christmas looking interesting with a hint of low heights to the S…

 

Would be cathartic after last year’s Christmas debacle!

Looking further ahead, the New Year period looks primed for further amplification near Scandi/Svalbard

 

I honestly think we have a 70% + chance of a midwinter SSW. The weakening Nina, high Eurasian snow cover,  cold southern strat analogs and crucially, continued blocking to the NE combined with indications the mjo could cycle towards 4–>7 late Dec all back up such an assertion.
 

Interesting times ahead, beyond the considerable mid term excitement For coldies.

[Cheshire Freeze]

7 minutes ago, Josh S said:

Christmas looking interesting with a hint of low heights to the S…

 

Would be cathartic after last year’s Christmas debacle!

Looking further ahead, the New Year period looks primed for further amplification near Scandi/Svalbard

 

I honestly think we have a 70% + chance of a midwinter SSW. The weakening Nina, high Eurasian snow cover,  cold southern strat analogs and crucially, continued blocking to the NE combined with indications the mjo could cycle towards 4–>7 late Dec all back up such an assertion.
 

Interesting times ahead, beyond the considerable mid term excitement For coldies.

A fair assessment.

I also think there's a good chance of a SSW.

All bets are off for Jan and/or Feb if that turns out to be the case.

 

 

Edited November 24, 2022 by CreweCold

[Liam Burge]

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!

[Penrith Snow]

1 hour ago, damianslaw said:

Divergence between ECM and GFS around the 96-120 hr timeframe, its rare we see divergence at shorter timeframes, so I expect to see them both aligning in by Saturday at least, tomorrow could well be another day of difference but given the changes to a blocked set up are forecast within the reliable now, i.e. around 30th, it would be surprising to see such marked differentials in the weekend runs. Its a cautionary post, ECM could very well swing to the GFS, but more likely the other way round. Don't shoot me down if its an ECM to GFS swing though..

Who could forget 'That ECM' almost 10 years ago in December 2012.

It was a 12h run and it was snow armageddon, alas it was gone 12 hours later replaced by a slack chilly high pressure.

The reason I bring this up is tonight's ECM is so different to GFS at 240 that I refuse to be drawn in just yet.

We will see.

Andy

[Don]

2 minutes ago, Penrith Snow said:

The reason I bring this up is tonight's ECM is so different to GFS at 240 that I refuse to be drawn in just yet.

Exactly, all still to play for!

[TSNWK]

References to that ECM ten years ago... I recall it well. A single op run that came out the  blue and disappeared the next.  

This time it seems to me that there is more substance with a slower pathway and holistically with other runs and means 

Eyes down for 18z... please send us on our way to the land of nod around 11 with sweet dreams instead of last nights heavy trudge to the pit at 10"15

 

[sheikhy]

5 minutes ago, TSNWK said:

References to that ECM ten years ago... I recall it well. A single op run that came out the  blue and disappeared the next.  

This time it seems to me that there is more substance with a slower pathway and holistically with other runs and means 

Eyes down for 18z... please send us on our way to the land of nod around 11 with sweet dreams instead of last nights heavy trudge to the pit at 10"15

 

Hmmm gfs 18z at 108 hours is it about to join ukmo/ecm!!!

[TSNWK]

1 minute ago, sheikhy said:

Hmmm gfs 18z at 108 hours is it about to join ukmo/ecm!!!

What you seeing different?

[sheikhy]

1 minute ago, TSNWK said:

What you seeing different?

Low cleared to the north and scandi high much further west covering the uk!!dont wana jinx it but looks like its backtracked!!

[Uncertainty]

Looks like last night’s run was an aberration!

 

[Mike Poole]

2 minutes ago, sheikhy said:

Low cleared to the north and scandi high much further west covering the uk!!dont wana jinx it but looks like its backtracked!!

Yes, 18z T132 v 12z T138 - much less or nothing made of the features highlighted on the 12z plot.

[TSNWK]

2 minutes ago, sheikhy said:

Low cleared to the north and scandi high much further west covering the uk!!dont wana jinx it but looks like its backtracked!!

You’re on to something looking better at 138… colder and clean

[E17boy]

Hi peeps

latest weather pattern expected later next week from today’s extended forecast, an easterly setting up. The presenter said that if this was later on in winter would have been beast from the east.  Anyone like to guess where we will go from here  we are so close.

THE SEARCH FOR OUR WINTER WONDERLAND RAISES OUR HEADS

[sheikhy]

Just now, Mike Poole said:

Yes, 18z T132 v 12z T138 - much less or nothing made of the features highlighted on the 12z plot.

One thing i mentioned earlier these 500mbs can be very misleading in terms of how cold the 850s are!!!!especially of the continent!!!

[minus10]

Well logged on to find over 90 posts to get through...wow the ecm 12z has set the thread alive tonite...

850 mean clearly heading down..

Gfs 18z so far looks better to me..

so...onward...

Edited November 24, 2022 by minus10

[cold snap]

There's actually to much blocking now 

[tight isobar]

Gfs 18z going into possible stonker territory into second sequence . We’ll highly likely now start seeing suite supports belly dropping!!