Model discussion highlights

[Eagle Eye]

Convectively coupled Kelvin waves (CCKWs) can be affected by the MJO and that modulates the general circulation of both the velocity potential but more importantly in Winter, the development and modulation of blocking and troughs generalised. It's very good guidance for generalised forecasting of extra-tropical coupling though it is by no means perfect of course. The modulation of these Waves is dynamically supressed and active convectively and that's relatively important in Winter time when working out the modulation of Tropical pressure systems and also any Winter time subtropical systems. Now it's important to note that the typical velocity potential extratropical reaction for these cold core systems (cold core according to Eric Webb, or rather cold frontal system) is that they will form on the backs of them with divergent fields (you can see that in the rotational backing behind the -VE VP) as the core of these typically evolve with +VE shearing though that's mainly during Summertime. It's clear that the irrotational VP vectors are ahead of the system that formed though you can sort of see why it formed where it did with the more characteristically 'rotational' vectors. It's important to note that this is still very much more of a characteristic used for Summer and CCKWs in Winter will of course rely on the initial packets of Rossby waves and it shouldn't really be used that much. Though it does help with the explanation for the formation of mid Atlantic blocking and more the subtropical system that just off the E North American Coast. 

Anyway, away from that and the general movement of Rossby-Kelvin Wave and MJO coupling is to suggest the extension of the +EPO and eventual movement into the -PNA but importantly the cyclonic wave breaking is linked with very strong +VE heights building towards Scandinavia based off the model trend. A pretty good variation of the January loaded TNH pattern looks to be the most likely here with the displacement of the Quebec -VE closer towards the central part of the USA and dynamically coupling closer to the East at times. The building of +VE heights along the SE and further North seems generally a stronger amplitude than the typical January pattern. Closely linked with the +EPO and that will tend to further the prospects for amplification downstream in the UK-Scandi area and that's a helpful driver for a few SSW composites.

MJO wise and though we are moving to the typically Nina style zonal phases so the return of wet weather around February disregarding a SSW may be possible, the likely +VE EAMT and Kelvin Wave Coupling given better MJO dynamics then around mid February may hint at possible colder opportunities and a VI event is unlikely at the moment for that time. I will likely do more later...

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792116

[Singularity]

With a trend to a stronger MJO presence across the Indian Ocean, it's no surprise to see a high over Scandinavia attempting to head toward Greenland.

Some excellent posts on here recently linking this back to the TNH (tropical northern hemisphere) setup and how that has been the catalyst for increased disruptive interference to the La Nina event (usually, the MJO is very quiet during a La Nina).

By Feb, the phase 3 response does become more (but not full-on) zonal, though not necessarily unsettled for the UK. Phase 4, on the other hand, is very much classical La Nina territory, so by then it will really depend on what the stratosphere is up to, in particular what pattern is propagating down from there, if anything at all.

I concur with Eric Webb regarding SSW chance & models underestimating that - there's so much going on that fit into the 'SSW precursor' bucket. Not that I'd dare give it more than a 50% chance at this stage, though!

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792274

[Mike Poole]

Both GFS (T192) and GEM (T210) poking Greenland with an atlantic ridge:

It later gets flattened, but worth continuing to watch.

Plenty of ensemble members from 0z (and the GFS op) going for a technical SSW this morning:

I’ll be looking to see if this trend continues, and increases, as it ticks down to closer range.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792293

[Uncertainty]

The scandi-Greenland dipole would be off the scale there. Lots of research correlates that pattern with SSWs. Maybe that’s why we’re seeing the huge 2nd phase of the warming in the strat in the extended. It’s there across the GEFS/ GEPS.

Even if we don’t split it first time (day 11/12) we might obliterate it altogether by the early Feb. 
 

The mjo in p3 isn’t normally great and perhaps  explains the westerlies on the 46, although there could be some flushing down of strat westerlies in the mix. 
 

Either way with the strat forecast and if that dipole comes off day 7 in the trop then I wouldn’t bet against an epic spell in Feb. The cold pool that has built over Siberia all winter is the prize. And what a prize it is.
 

February is absolutely up for grabs. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4791624

[Uncertainty]

Also the day 8+ trend today is retrogression of the U.K. / Scandi ridge —> height rises in the Atlantic. Check out the more vertical jet profile of the pub run near Greenland compared to the 12z

18z

 

12z

 

Clusters at 264 also keen on Atlantic height rises. The SPV leaving that area leaves the door ajar. 

 

GEPS on the same page

 

A flattening in the morning takes us back to a U.K. high. A correction north and things get really interesting.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4791641

[Vikos]

4 minutes ago, Sweatyman said:

Every year without fail. Big Greek snow dump

ΥεΣ ιηδεεδ. ωε λικε ξηοω αλοτ. ωε αρε chionomaniacs…

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792580

[Catacol]

19 minutes ago, minus10 said:

On the face of it this doesnt look like a bad EC 500 anom 12z..10 day

...higher than average heights stretching from south of Greenland accross the Pole to the Aleutian side with lower than average heights in most of med and to the west of Spain..helping to weaken or split the trop vortex??....however we know that anomalies can be deceptive ... except that the actual mean i think is not a million miles away from this...

...mmm....

 

It's a decent looking anomaly and mean combo. We have all seen much worse. The frustration overall - unless in the far north or fortunate spots that have come good - is that 2 cold spells so far this winter are not looking like they will produce widespread snowfall. I'm yet to see a single flake and didnt see one either last year! Both cold spells (early Dec and now mid Jan) have produced more depth of cold than many might have expected prior to their arrival but lack of precipitation is noticeable because both cold patterns have been pretty stagnant. It really is tough in the UK to get things to click for snow.

Retrogression of the pattern as momentum drops now strongly backed by the ensembles, but the blocking signal looking more mid than high lat. 

The mid lat option as this frosty spell this week comes to an end is looking increasingly favoured. Still thinking the biggest player going forward from here will be the rebounding impacts of changes to the SPV. And one thing is for sure - if the SPV does take a really significant hit (and ideally split) then bin all and any NWP forecasts at long range because they genuinely won't have a scooby as to what happens next. NWP modelling has a lot more vertical resolution than was the case in the past but is still a long way from being able to predict accurately speed of downwell and/or movement of vortex shards. Anomaly forecast for the SPV continues to move in the right direction:

And this means I dont think anyone can predict what is going to occur out beyond 240h at the moment. Crossroads moment, buckets of uncertainty.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792783

[Mike Poole]

ECM clusters.  T192-T240:

Most have us under  the SE flank of a high, but 2 and 5 have more blocking to the NW.  If I squint and look at these, bearing in mind the shenanigans above, there’s an Atlantic ridge through Greenland block there, vortex relocating to Asia,  maybe not cluster 4.  

T264+: 

Sacks of uncertainty there, certainly some cold potential, but probably not worth dwelling on for now, will look different next run!

One thing that occurs to me, is that GFS runs have shown the warming in the strat in at least 2 big stages, possibly 3 on the 12z.  Can we be seeing something in the trop which is unfinished business from the first warming in the strat, before the other ones finish the job?  Therefore, a work in progress, transitional pattern.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792578

[Derecho]

31 minutes ago, blizzard81 said:

Just to add to the mix, biggest sun spot in years has now formed and is directly facing earth. Not news I wanted to hear. In fact we may be seeing more charts like this in the next few days if the sun has it's way. Latest gfs run. 

There is no academic research which suggests sunspots have an impact on subsequent days weather, there's just too many other things going on to be able to pick its influence out. In fact even when looking at whole winters with no sunspot activity there is no obvious link.

From Lockwood (2010). CET on Y axis, solar flux on x axis.

If there is no clear relationship when looking at years without any sunspots, how can we possibly say any milder output if it materialises next week is due to sunspots? You'd think if it had such a big influence on our weather, the signal would show up a lot more clearly over the course of a winter.

Usually people like to blame sunspots when a cold forecasts goes wrong to make themselves sound good and give themselves an excuse.

There have been plenty of cold winters when solar activity has been high.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792985

[MattH]

1 minute ago, mountain shadow said:

I may be wrong, but I do not believe that the consensus of a front loaded Winter due La Nina analogues factored in a potential SSW at the end of January.

Looking at the MJO, we may get the holy grail of the MJO being in a favorable phase just as the impacts from a SSW start to influence on the trop in mid to late February. 

All eyes on the top of the world.

Morning...

Just wanted to start with quoting the above as, essentially, that is exactly the long-term outlook as things stand. As usual it is always seemingly a waiting game but once again we must look at the current weather and acknowledge what is a pretty decent cold spell, with snow for some, cold days and very cold nights, this lasting into the forthcoming weekend too away from the N and W.

Those hoping for any sort of higher latitude blocking pattern in the short-term will still likely be dissapointed, that includes Scandinavian highs and E'lies. The AAM remains negative and there continues to be clear evidence for +ve, W'ly AAM anoms to remain dominate through the mid-latitudes, this essentially stopping or not helping in the building of higher MSLP anoms to higher latitudes, essentially any block gets the top knocked off it, as perfectly exampled with the synoptics in the coming days.

The blocking high which is set to dominate the second half of January carries high confidence though, as does a drier than average outlook, clearly welcomed after the very wet first half to January. It is the temperature trends which are very uncertain as clearly if the high pressure has a primary COG to the south of the British Isles then a very tedious spell of overcast grey laden skies, damp and mild weather will dominate, this happened for weeks one January in the last few years and was unpleasant, especially those with SAD. However, at the moment that doesn't seem to be the case, overall, moving forward with the high more directly located over the British Isles and with a day-on-day reduction in temperatures and colder nights developing, but clearly not to the same extent as currently. How the high evolves and wonders around will, again, be key to temperature trends and sensible weather at the surface and a colder N or NE'ly feed around the high does remain possible.

Coming back to the quote above and this is exactly how I (and others) see the long-term panning out. A default +ve NAO end to winter, as per the seasonals, IMO is not likely. The MJO will move back through the I/O and into the Maritimes and, potentially, on into the W Pacific as well into early February, this coming at a perfect time when any sort of disruption to the strat vortex aids in reducing the westerlies in the troposphere, eventually at least. How all this will play out is very uncertain though, but the seasonal models, going for a +ve NAO wet and windy end to winter carry a low likelihood and, again, IMO, I have a feeling the key period for anything significant moving foward will be after the opening week of February and more likely mid-February onwards.

Clearly, at that point in the winter for those hoping for significant winter synoptics do need to start hoping for significant flows from the E and NE, perhaps N, a polar NW'ly like at the moment will not have the same potency. Whether an SSW will occur, officially, remains to be seen, but with the MJO swinging back around and with the strat vortex, at a minimum, on its knees, if not already KO'd then that is a strong base state for blocking patterns through late winter and early spring and not a +ve NAO outlook.

Plenty of interesting times ahead I feel...

Kind regards, Matt.

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793286

[bluearmy]

We’re a week away from seeing the upper strat reverse above 80N. In the days that follow, gfs sees that reversal spread further down and south (but not to the extent that it reaches 10hpa/60N and becomes a tech ssw) 

We are still likely a few days away from most of the modelling having a decent handle on what follows in the lower strat and trop - I have a recollection that it was icon which handled the last reversal better than the other models in the trop (I could be wrong). For the time being, it’s a watching brief from me and little to be analysed in week 2 because I see little point.  

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793219

[mountain shadow]

3 hours ago, Penrith Snow said:

We have to be realistic and expect a westerly February which to be honest all the seasonal models predicted in late Autumn. Linked of course to the El Nina signal.

The consensus was for a front loaded winter and in some respects we have had that with a cold December and our current cold spell 

If it’s mild now from Saturday to early March this winter will still have been better than many in recent years.

Andy

I may be wrong, but I do not believe that the consensus of a front loaded Winter due La Nina analogues factored in a potential SSW at the end of January.

Looking at the MJO, we may get the holy grail of the MJO being in a favorable phase just as the impacts from a SSW start to influence on the trop in mid to late February. 

All eyes on the top of the world.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793275

[Catacol]

4 hours ago, Bricriu said:

Just in relation to mid February cold chances, is the MJO by then predicted to be in a phase favourable for blocking? 

Depends how fast it moves. Usually 30-60 days cycle - so we were phase 7 first week of Jan. Mid Feb certainly possible to repeat. What is notable is the strength of the MJO this season in a Nina ENSO context. Quite active and certainly active right now in the IO (Indian Ocean)

There are many possible combinations of late winter patterns lining up for us in this very interesting winter. MJO progression is one element. Shape of SPV disruption and whether it splits, displaces or does neither is another and I continue to hold my breath on this. Timing of next pacific jet extension will play a part linked to future EAMT events, hard to forecast. 

But at least we are in the game. Someone earlier said that the single element definitely absent for the end of this month and heading into February is a strong SPV connecting to a strong TPV and driving westerlies. Whatever else happens going forward that is a good starting point.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4792730

[Met4Cast]

14 hours ago, Don said:

You do see the possibility of colder weather again mid February onwards though?

Yes, my thinking re: a colder period during the 2nd week - mid February ish is irrespective of any potential SSW. The MJO moving into phase 3 suggests height rises to the W/NW in the Atlantic, given the lag that puts us in the mentioned timeframe above. 

Current EPS trajectories (as mentioned above) suggest height rises across Europe/Scandinavia before transitioning towards a -NAO, i.e the high likely retrogressing west into the Atlantic at some point, following the MJO signal.

This developing at a time of a weakening SPV (SSW or not, strong signs of below average u-wind strength) may, with a little bit of luck lead to some high latitude blocking & cold patterns for the UK/NW Europe. We do have westerly momentum continuing in the Atlantic but as u-wind strength decreases & we see a lifting out of the TPV/SPV from Greenland this should begin to reduce & may allow for a Greenland block of some sort to develop. 

My worry.. is a full blown SSW may interrupt the above expected evolution. The SSW is a wildcard. The direction of travel currently is towards colder patterns being most likely, an SSW disrupting that may mean we miss out on a trop led cold spell, likewise an SSW could potentially amplify any blocking patterns leading to the potential for a more potent, prolonged period of cold although any SSW impacts on the trop wont be known for a fair while yet, if an SSW even occurs. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793419

[mushymanrob]

February SSWs?

Again a cursory overview but i make it that there were 12 since 1958.

8 February SSWs had no real cold spell following
4 did


I might investigate SSWs further.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793326

[nick sussex]

The trop effect from a SSW does vary according to the base state of the AO at the onset .

In a nutshell the research suggested that the trop effects are enhanced if the AO is positive and the effect weakens as you move towards an already negative AO.

It does make sense if you think about it . 

 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793372

[phil nw.]

Even without a full blown technical ssw It looks like we are starting to see the effects of a weakening spv showing in the later frames.

I would think the slowing down of zonal winds and the coming spv displacement will eventually create more gaps in the 500hPa pattern over the Arctic.

The immediate outlook of a UK high is not a bad place to be whilst we wait to see if we can benefit from the warmings above.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793519

[Tim Bland]

Now seems like a good time to remind everyone that GEM often scores higher than GFS in verification scores and is often first to pick up a signal that the ECM then latches onto as they use similar data ….

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793523

[nick sussex]

The ECM although interesting still comes up short because the jet doesn’t cut back sufficiently sw and the high centre is too far south .

The high will likely topple as we seem unable to get a clearance of the PV from the north . Because of that the base start position has to be sufficiently north .

The trigger shortwave which is over Denmark needs to cut back sw towards the Low Countries .

The high centre needs to be further north .

Even if we see improvements in these set ups you need to see the jet cut back modelled at much closer range because that’s  crucial to get the ne e flow and  the messenger which delivers the verdict is the trigger shortwave .

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793624

[CoxR]

I think it's fair to say the GEM ensemble is pretty keen on an SSW...

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793564

[Cold Winter Night]

I think it's been a while since we've last seen such agreement between EC and GFS at 192h? 

And at 216h still, except for the East-Siberian High:

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793607

[Cambrian]

The 12z ECM (and GFS / JMA) op for day 10 is fascinating. Low heights extended along some very southern reaches, all the way from Algeria to India. It is part of a massive Eurasian spill of cold air, resulting in southerly troughing and a lot of cold air a long way south. 

   

It looks like being just a matter of time before the cold gets here. The Atlantic, as probably doesn’t even need saying any more, is absent from normal duty, and it’s up against all that cold air in any case. So it’s given up the ghost and is housing the block formed by all those heights fleeing Europe, that would of course have been pushed west by the rush of cold air through Eurasia. This is retrogression dynamics on an industrial scale. 

Coming back to day 7, the 12z ECM op has a ninja rabbit and the ensemble mean has a soft focus ninja rabbit,

   

both flirting with delivering us a northerly, being obstructed by the high to our southwest, the position of which is being maintained by the low heights and cold over the Mediterranean, preventing it moving east while raising the possibility of the formation of a fully fledged cold European low; and the Labrador Sea trough being fed by the Canadian lobe of the PV, preventing it from moving west.

Looking at the spread, the low Euro heights look a cert, the Labrador Sea trough and even the Canadian lobe itself, much less so. 

It all suggests that if the high is going anywhere, that’ll be northwestward, leaving a choice between Arctic or Eurasian cold (or indeed a mix of the two around the northern flank of a European low) free to spill south and west over the UK and Ireland to finish the job that is winter 2022/2023. 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793722

[bluearmy]

Flatter ec follows the eps 12z

without the cross section strat charts for ec it’s tough to know what’s forecast beneath the reversals high up - gfs keeps the lower strat stronger than we’d like to see above 65N until around the 28th.  Based on this you’d say that mobility in the Arctic sector will most likely prevent any HLB establishing until first week feb.  But I’m still cautious about accepting the mid/lower strat forecasts - should become more confident in three or four days. Again the 46 this evening will be watched to see what it thinks about zonal flow up there over the next two weeks 

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793884

[Mike Poole]

14 minutes ago, feb1991blizzard said:

slight problem now is we don't know if its an outlier suite so will it skew the £C46 - expect a big SSW signal later when it comes out.

Quite.  I am looking at the ECM 46 really for the first time this winter (I’ve avoided it in the past on chocolate teapot grounds) particularly to try and get a heads up on what ECM models are saying about the strat developments.  One thing I’m learning is that it is best viewed with a strong memory of the 0z ECM ensemble suite on which it is based, which isn’t a ringing endorsement of attempting to forecast modelling at the 46 day range!  

I’ve not posted the clusters for a few runs, I’m struggling to see much pattern in the extended, here’s the last 3 runs T264+, today’s last:

Today, at least there are only 3 clusters, cluster 1 has little no blocking, cluster 3 has significant blocking!  Maybe, you could argue a cluster with a significant strat warming is showing its hand, but it is still very much in the noise.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4794026

[fromey]

The warming getting going on the 10hpa, but still below the average and the 30hpa warming slowly but still well below the average.

Original post: https://community.netweather.tv/topic/98196-model-output-discussion-new-year-and-beyond/?do=findComment&comment=4793990