Model Output Discussion - mid Autumn

[Ali1977]

2 minutes ago, Mike Poole said:

Strat vortex taking even more of a hit on this one, T330:

Certainly does, weakened and stretched considerably in FI 

[Met4Cast]

Okay.. 

Let's break down whats happening in real time with the global drivers & see what they're suggesting for the next two weeks and whether or not they're showing anything resembling support for the high latitude blocking appearing on a few runs. Remember the weather doesn't just "do"  things, there is always a reason behind the weather patterns that we see, NWP attempts to make sense of these drivers & predict a possible way forward.

What has happened up until now? A strong westerly wind burst event occurred in the Pacific just west of the dateline, this injected westerly momentum into the overall wind flow budget which sent AAM tendency surging upwards, the prolonged nature of the WWB event and transition east helped to keep AAM tendency positive for a while, this triggered a rise in both Frictional Torque (+FT) and Mountain Torque (+MT) pushing global atmospheric angular momentum (AAM) into positive territory, for a time we had a ocean/atmospheric coupling with the ENSO base state (El Nino).

AAM charts:

If you look at the right AAM chart above, we can see that some of these positive AAM anomalies did transfer northwards towards the pole, albeit not with any particular 'oomph' or real amplification (Atlantic ridge signal). Meanwhile, the MJO was slowly transitioning through a very low amplitude phase 8 which correlates broadly to a, you guessed it, mid Atlantic ridge. Note how broadly similar this MJO phase 8 composite for November is to this weekends pattern;

That is the signal for this weekends Atlantic ridge which models initially struggled with, the tropics & subtropics working in tandem. GFS initially being too amplified and ECM being too flat just to keep it broad. Going into this weekend we will see HP amplify and colder air will sink southwards across the UK. This is now well signposted within broader model outputs and accepted as the evolution going forward. 

Also note the extension of the high NEwards towards Scandinavia.. not a true Scandi high but just an extension, practically what the EPS are showing (See the @Mike Poole's cluster examination from earlier highlighting this)

Now.. we're seeing a reversal. Referencing the AAM and Hovmöller charts above, the WWB event has waned and the atmosphere in an attempt to rebalance momentum reverses to easterlies, this tanks AAM tendency and we're beginning to see a fall in overall GLAAM as a result. Meanwhile, the MJO will be transitioning through a relatively high (compared to recent) amplitude phase 1-2 which correlates to HP moving eastwards towards Russia and low pressure from the Atlantic taking over, broadly a typical "zonal" signal, i.e high pressure to the south, low pressure to the north, less south shifted than we've seen recently. 

With all of this in mind, the GFS doesn't seem particularly plausible, but the ECM solution does. I doubt the ECM has it exactly right re: details but the signal from the EPS is very much in line with everything I've discussed here. Cold next week, yes. Wintry? Perhaps in places, but a prolonged spell of high latitude blocking looks very unlikely and I suspect the GFS will end up with some egg on it's face. It's not too dissimilar to the ECM it's just probably over-doing the amplification. 

The signal going forward through early December at the moment is overwhelmingly to one of Atlantic driven weather with the worst of the unsettled weather in the north. I suspect we will eventually see NWP outputs beginning to reflect this once the reversal to easterlies in the Pacific starts to feed back into NWP initialisation data in real time.

Beyond that? Well, now it starts to get exciting. On the Hovmöller above we can see the next MJO wave expected for December beginning to appear in the Indian ocean. This could be more amplified, trigger another more substantial rise in AAM and cycle round into phases which support proper blocking in a hopefully a more amplified state. Late December/early Jan holds a lot more potential.

Edited November 22, 2023 by Met4Cast

[rwtwm]

1 hour ago, jmp223 said:

Regardless, this is the most promising start to the winter thread I have seen for a good few years.   I think if, in September we were offered this setup guaranteed for late Nov/Dec the vast majority would take it in a heartbeat.  A lot of positive signals (for cold/blocking)

You're not the only person to make this statement. But it's worth reminding everyone that the first half of last December was the coldest since 2010 - sample analysis charts from Dec '22 below. 

 

Separately, was it 2019/20 that started with a really disorganised vortex, then an SSW threw us into a mild high? 

Can't help but be reminded of that (even if I have the year wrong), when I see excited posts about an SSW against this starting point.

Of course, there's still time for everything to flatten out. But looking naively at the 00z ensembles it's looking promising that a second consecutive winter will start with a below average spell.

*Edit to save clogging the thread*

Excellent post from @Met4Cast above. I've struggled to get my head around AAM (not what it is, but what it's impacts are likely to be). That discussion has helped me massively.

Edited November 22, 2023 by rwtwm

[TSNWK]

Just now, Ali1977 said:

Certainly does, weakened and stretched considerably in FI 

Nice.  But can we place much trust in it when last night warming was over Canada?

[Robbie Garrett]

Does @Glacier Point still frequent these forums?  His views on the models were awesome  

Edited November 22, 2023 by Robbie Garrett

[Paul_1978]

1 minute ago, Robbie Garrett said:

Does @Glacier Point still frequent these forums?  His views on the models were awesome  

According to his profile he hasn't logged on Netweather for over 3 years since October 2020 so I guess not.

[Robbie Garrett]

1 minute ago, Paul_1978 said:

According to his profile he hasn't logged on Netweather for over 3 years since October 2020 so I guess not.

Just checked. That's a shame

[Premiere Neige]

Just read an interesting article from the BBC about how the Canadian wildfires have warmed the stratosphere, something I hadn't even considered and may explain why the models are sniffing around a Canadian warming. Posted the article in the Strat forum if anyone is interested...

[ANYWEATHER]

Regardless of all the scrutinising over the models , to my eyes ,gfs and ecm ,today ,have upgraded the cold in the days ahead ,on the other hand ,caution is still needed, but coldies should be happy today of the output....☺

[Mike Poole]

9 minutes ago, Met4Cast said:

The signal going forward through early December at the moment is overwhelmingly to one of Atlantic driven weather with the worst of the unsettled weather in the north. I suspect we will eventually see NWP outputs beginning to reflect this once the reversal to easterlies in the Pacific starts to feed back into NWP initialisation data in real time.

Good post, very clearly set out.

The bit I am having trouble with, is the bit I’ve quoted.  Where is the signal for this, because it really isn’t on any of the model output (except possibly at day 15 on cluster 2 of the EPS).  I guess we need to wait and see, but I’m also thinking of the strat evolution here and vortex placement, at the moment that would seem to go against unsettled Atlantic driven weather on the same timescale.

[summer blizzard]

11 minutes ago, rwtwm said:

You're not the only person to make this statement. But it's worth reminding everyone that the first half of last December was the coldest since 2010 - sample analysis charts from Dec '22 below. 

 

Separately, was it 2019/20 that started with a really disorganised vortex, then an SSW threw us into a mild high? 

Can't help but be reminded of that (even if I have the year wrong), when I see excited posts about an SSW against this starting point.

Of course, there's still time for everything to flatten out. But looking naively at the 00z ensembles it's looking promising that a second consecutive winter will start with a below average spell.

The winter of 2020 did not see a SSW. People are perhaps remembering 18/19 which saw a SSW in very early January however December was already mild. Quiite a lot of SSW's do just generate a 2 week polar block before a UK high for a month (2009, 2013, 2019), additional cold if it comes is from another attack on a weak ish vortex. 

[Battleground Snow]

Easterly inbound as early as Monday according to the JMA 

[Catacol]

14 hours ago, Severe Siberian icy blast said:

I have to admit im becoming very interested in what a week ago or so was little more than a brief snap with the expectancy of what was already a record breaking PV high up to filter down into what ultimately would become a stormy December, 

The weather makes us all eat the egg but isn't it fascinating how it seemingly makes its own mind up some of the time and its only with the Wonderful aid of hindsite we look back and make sense as to how it came about its a forever learning curv,

We have a tripol which seems to have came out of nowhere?  

A very amplified jet stream curving back on itself through the UK.

 

And to be honest we could be looking at 4 wave pattern which will mean it could be either very rewarding or very frustrating but a very slow moving locked in pattern could become apparent and the Canadian warming that's also come through the back door is going to become a major player along with where segments of vortex' become established, this will be a stand of between spawning areas of low pressure off it interacting with high pressure features pushing and giving off one another, and this could be exciting! 

We need a cold winter

 

You make an interesting point about the Atlantic Tripole. The extent to which it has come out of nowhere I don't know. I am guessing - and happy to be shot down by someone who knows better - that our understanding of the layers through the oceans is much less advanced than our understanding of atmospheric layers. ENSO forecasts are certainly not especially accurate and if there is a forecast mechanism for the Atlantic I have never seen it. Whether the tripole, which used to get quite a lot of discussion back in the early internet days, ends up being a big topic of conversation this year we will need to wait and see. But whatever the cause, and the ins and outs of reading a pattern like this in advance, it has a good look to it.

By extension, here's a thought. NWP is driven by the data put into it. Is data on forecast SST profiles in the atlantic part of that data stream - or is this a data vacuum with perhaps only the starting point included? There must be acknowledged areas of data and modelled data acquisition that the modellers themselves know is lacking. The ENSO forecast must surely feature in seasonal projections but is ENSO the only ocean forcing thrown in? Would be interested to know.

[CameronWS]

1 hour ago, Met4Cast said:

From a true Greenland high on the 00z

To a sortof flabby huge surface high on the 06z 

Consistent, then..

 

Yet just as good for cold in the short term? Inconsistency with the heights but still a pretty good outcome for cold based on what I can see. Also a broad theme that is showing across all models.

[MATTWOLVES 3]

20 minutes ago, Mike Poole said:

Good post, very clearly set out.

The bit I am having trouble with, is the bit I’ve quoted.  Where is the signal for this, because it really isn’t on any of the model output (except possibly at day 15 on cluster 2 of the EPS).  I guess we need to wait and see, but I’m also thinking of the strat evolution here and vortex placement, at the moment that would seem to go against unsettled Atlantic driven weather on the same timescale.

Yes Mike...This is a point I always bring up regarding those background drivers...yes they influence the weather further down the line....but what happens when other little variables enter the frame and change the outcome! Then we have to factor in the fact that the PV has the power to overule them all. Even a displacement could alter where we are heading at an early juncture. Also the ENSO tends to rule the states more so than its influence across the UK and Europe,where the PV tends to rule supreme.

Edited November 22, 2023 by MATTWOLVES 3

[Met4Cast]

19 minutes ago, Mike Poole said:

Good post, very clearly set out.

The bit I am having trouble with, is the bit I’ve quoted.  Where is the signal for this, because it really isn’t on any of the model output (except possibly at day 15 on cluster 2 of the EPS).  I guess we need to wait and see, but I’m also thinking of the strat evolution here and vortex placement, at the moment that would seem to go against unsettled Atlantic driven weather on the same timescale.

EC46 is also starting to show a signal for this. We're probably looking late week 1 into week 2 really. The Atlantic ridge may prove to be fairly robust. 

[BartyHater]

7 minutes ago, Met4Cast said:

EC46 is also starting to show a signal for this. We're probably looking late week 1 into week 2 really. The Atlantic ridge may prove to be fairly robust. 

That`s an interesting looking anom setup. Can I ask where the 46 can be viewed please?  

[northwestsnow]

Next week aside Fri and Sat look really cold - perfect seasonal weather for Xmas Markets certainly frost setting in by 9pm fri/sat..

I think we need some modelling consensus on the troublesome little low before we go into next week but all things being equal an old skool end of November looks a good shout - more fog and frost

[booferking]

Arpege at it again 06z

[Chesil View]

50 minutes ago, Met4Cast said:

Okay.. 

Let's break down whats happening in real time with the global drivers & see what they're suggesting for the next two weeks and whether or not they're showing anything resembling support for the high latitude blocking appearing on a few runs. Remember the weather doesn't just "do"  things, there is always a reason behind the weather patterns that we see, NWP attempts to make sense of these drivers & predict a possible way forward.

What has happened up until now? A strong westerly wind burst event occurred in the Pacific just west of the dateline, this injected westerly momentum into the overall wind flow budget which sent AAM tendency surging upwards, the prolonged nature of the WWB event and transition east helped to keep AAM tendency positive for a while, this triggered a rise in both Frictional Torque (+FT) and Mountain Torque (+MT) pushing global atmospheric angular momentum (AAM) into positive territory, for a time we had a ocean/atmospheric coupling with the ENSO base state (El Nino).

AAM charts:

If you look at the right AAM chart above, we can see that some of these positive AAM anomalies did transfer northwards towards the pole, albeit not with any particular 'oomph' or real amplification (Atlantic ridge signal). Meanwhile, the MJO was slowly transitioning through a very low amplitude phase 8 which correlates broadly to a, you guessed it, mid Atlantic ridge. Note how broadly similar this MJO phase 8 composite for November is to this weekends pattern;

That is the signal for this weekends Atlantic ridge which models initially struggled with, the tropics & subtropics working in tandem. GFS initially being too amplified and ECM being too flat just to keep it broad. Going into this weekend we will see HP amplify and colder air will sink southwards across the UK. This is now well signposted within broader model outputs and accepted as the evolution going forward. 

Also note the extension of the high NEwards towards Scandinavia.. not a true Scandi high but just an extension, practically what the EPS are showing (See the @Mike Poole's cluster examination from earlier highlighting this)

Now.. we're seeing a reversal. Referencing the AAM and Hovmöller charts above, the WWB event has waned and the atmosphere in an attempt to rebalance momentum reverses to easterlies, this tanks AAM tendency and we're beginning to see a fall in overall GLAAM as a result. Meanwhile, the MJO will be transitioning through a relatively high (compared to recent) amplitude phase 1-2 which correlates to HP moving eastwards towards Russia and low pressure from the Atlantic taking over, broadly a typical "zonal" signal, i.e high pressure to the south, low pressure to the north, less south shifted than we've seen recently. 

With all of this in mind, the GFS doesn't seem particularly plausible, but the ECM solution does. I doubt the ECM has it exactly right re: details but the signal from the EPS is very much in line with everything I've discussed here. Cold next week, yes. Wintry? Perhaps in places, but a prolonged spell of high latitude blocking looks very unlikely and I suspect the GFS will end up with some egg on it's face. It's not too dissimilar to the ECM it's just probably over-doing the amplification. 

The signal going forward through early December at the moment is overwhelmingly to one of Atlantic driven weather with the worst of the unsettled weather in the north. I suspect we will eventually see NWP outputs beginning to reflect this once the reversal to easterlies in the Pacific starts to feed back into NWP initialisation data in real time.

Beyond that? Well, now it starts to get exciting. On the Hovmöller above we can see the next MJO wave expected for December beginning to appear in the Indian ocean. This could be more amplified, trigger another more substantial rise in AAM and cycle round into phases which support proper blocking in a hopefully a more amplified state. Late December/early Jan holds a lot more potential.

Met4cast. Your final two paragraphs could be describing December 1962. 

When after a blocked cold start the month became Atlantic driven with the worst of the weather in the north. Before things started to get exciting in late December/early Jan................. Mind you of course back then November 62 had a Canadian warming event...............oh hang on hasn't this November got one too.  

[The Enforcer]

1 hour ago, Met4Cast said:

From a true Greenland high on the 00z

To a sortof flabby huge surface high on the 06z 

Consistent, then..

 

I am not surprised. At a range of T+200, I very much doubt any of the models are from run to run.

[TSNWK]

2 minutes ago, booferking said:

Arpege at it again 06z

Annoying this.  ARPEGE does ok at short range so a tad concerning its brought that low south and is pumping up vortex over Greenland... 

[Met4Cast]

16 minutes ago, BartyHater said:

That`s an interesting looking anom setup. Can I ask where the 46 can be viewed please?  

Sure!

ECMWF | Charts

CHARTS.ECMWF.INT

 

[BartyHater]

1 minute ago, Met4Cast said:

Sure!

ECMWF | Charts

CHARTS.ECMWF.INT

 

Thanks, much appreciated. 

[booferking]

1 minute ago, TSNWK said:

Annoying this.  ARPEGE does ok at short range so a tad concerning its brought that low south and is pumping up vortex over Greenland... 

But the high looks locked in place will erode the vortex