Model Output Discussion - Into February

[Nick F]

9 minutes ago, minus10 said:

Uk...hp magnate..

Yep, just cannot seem to shake off high pressure throughout the 06z op so far, more so the south. Hopefully it will ridge north, northwest or northeast when we finally get some amplification, though could be a while looking at the MJO progression to the western Pacific which favours this ...

[Gowon]

4 minutes ago, Ali1977 said:

It’s FI , and will change next run. It’s Just time to look for hints of a change rather than definite direction 

Indeed, and like Nick said, it's good to see that extra amplification on this run

[Spah1]

I’m no chart expert but surely we should see some sort of favourable cold weather off this. 

[Met4Cast]

It’s worth emphasising that an SSW does not guarantee UK cold weather, especially displacement events. Split events are more reliable. 

Another potential factor is the disconnect between the strat & trop. It’s plausible that an SSW fails to downwell & impact the surface levels, this is more likely when there is such a stark disconnect as we’re seeing forecast at the moment. 2019 is a good example of this, the UK ended up with above average temperatures following that SSW. A warm March that year!

 

A displacement event seems most likely based on the GEFS/EPS and a quick trop response looks unlikely based on the current configuration of the atmosphere. 

So.. end of Feb/early March at the earliest, if we even see impacts from any potential SSW. 

It’s not the magical path to certain cold many seem to believe it to be. 

Edited February 5, 2023 by Met4Cast

[Daniel*]

12 minutes ago, Nick F said:

Yep, just cannot seem to shake off high pressure throughout the 06z op so far, more so the south. Hopefully it will ridge north, northwest or northeast when we finally get some amplification, though could be a while looking at the MJO progression to the western Pacific which favours this ...

GEFS seem more favourable with phase 6-7 . 
 

[bluearmy]

56 minutes ago, Met4Cast said:

It’s worth emphasising that an SSW does not guarantee UK cold weather, especially displacement events. Split events are more reliable. 

Another potential factor is the disconnect between the strat & trop. It’s plausible that an SSW fails to downwell & impact the surface levels, this is more likely when there is such a stark disconnect as we’re seeing forecast at the moment. 2019 is a good example of this, the UK ended up with above average temperatures following that SSW. A warm March that year!

 

A displacement event seems most likely based on the GEFS/EPS and a quick trop response looks unlikely based on the current configuration of the atmosphere. 

So.. end of Feb/early March at the earliest, if we even see impacts from any potential SSW. 

It’s not the magical path to certain cold many seem to believe it to be. 

The eps mean has lost an ssw on the 00z run 

The spv tracks east into n Russia at too high a latitude because the Canadian ridge doesn’t exert enough pressure.  not worth taking much from one run but the momentum is broken on the eps and note that the gefs haven’t yet shown a mean reversal. 

will the decimation of the zonal flow late feb be enough if trop telecons dicate ??

[Cambrian]

A high flyer 1048.8 mb on my Davis rig here at 11.33am, -2.3 degrees overnight, beautiful crisp morning but surprisingly hazy, quite a lot of high cloud. However, the pressure is very likely to fall away sustainedly from now through to mid month, as on the 0z ECM ensemble mean - the op and control even keener on a change to cyclonic weather, with a quite different feel possible by then. 

To be sure, the 0z ECM and GEM ops are going a bit Rollerball Rocco with the low to our north at day 10, a bit early to say whether it will be full-on maniac, but either way, probably the best chance of getting some colder uppers in around mid month, as all the cold air has been removed from Europe by then - mild from the Mediterranean to the Baltic. 

   

The GFS not on board with this so far today, but had similar for day 11 on its 12z run yesterday, and the development of low pressure to the north of Scotland enjoys good support from the ensemble means, like from the 0z ECM here, for day 10. 

 

I quite like the ECM development in particular, as shown in the op and mean anomalies…

 

as the deeper low cleanly punches through the heights to the south, between us and Portugal, keeps the Azores high further west, forcing heights northwest, leaving us open to those colder digs from Greenland. 

Indeed, there’s some generally good looking trends for a build of heights just off the Canadian seaboard up towards southwest Greenland, which with the Pacific not being so sure of itself, might be all the help we need in pulling us round into a truer northerly in time. The cross-polar trough is aligned nicely, and could deliver a cheeky little cold spell just after mid month if sufficient heights can move up the western side of Greenland and keep the Canadian lobe of the PV mollified. With the jet stream continuing to be restrained in that long hold, only slow manoeuvring going on, winter is far from being on the ropes and there could still be a lot worth wrestling with as we move on through February. 

[bluearmy]

Gfs op shows what the fall out could be be reversal with flow in the lower strat and trop. No westerly momentum left to push down into the last third of feb  

Today                                                             Day 16 

      

[ribster]

4 hours ago, Purga said:

Sh*tesville beckons..

150.02 kB · 0 downloads

You posted a similar thing around a week or so ago saying at least the 7th will be mild, looks anything but...

[Tamara]

1 hour ago, Met4Cast said:

It’s worth emphasising that an SSW does not guarantee UK cold weather, especially displacement events. Split events are more reliable. 

Another potential factor is the disconnect between the strat & trop. It’s plausible that an SSW fails to downwell & impact the surface levels, this is more likely when there is such a stark disconnect as we’re seeing forecast at the moment. 2019 is a good example of this, the UK ended up with above average temperatures following that SSW. A warm March that year!

 

A displacement event seems most likely based on the GEFS/EPS and a quick trop response looks unlikely based on the current configuration of the atmosphere. 

So.. end of Feb/early March at the earliest, if we even see impacts from any potential SSW. 

It’s not the magical path to certain cold many seem to believe it to be. 

I live in Portugal, and am therefore detached from the interest in this thread, but you are correct in respect of the over "magic bullet" association to cold weather with SSW's. As interesting a phenomenon they are in themselves, the associated cold weather hype rather detracts from that appreciation. Similarly with the MJO - this is not the stand alone phenomenon it is treated as in this thread and equally as such not a magic bullet to cold weather preferences. It is just one part of the atmospheric circulation total wind-flow budget, and while clearly an important catalyst for changes in weather pattern, it has to be taken in association with the rest of the wind-flow budget which comprises the extra-tropics. The relationship between the tropical & extra tropical wind-flow circulation does not work on a linear x+y = equation (in the same way as the troposphere and stratosphere can have both a connected & equally often quite disconnected relationship). With this in mind the frequent use of MJO composites on this thread is not going to lead to accuracy, especially when attempted to be fitted to weather bias patterns, without considering the extra-tropical Global Wind Oscillation (GWO). The GWO incorporates analysis of the total circulation budget and gives analysis of each flux and torque component within the total atmospheric circulation and is therefore a much more accurate guide. That is, again, if one is willing to suspend skewing.such a diagnostic to try to fit to a desired outcome. This will also lead to inevitable error (and disappointment)

So to put some of this background rationale into practice:

The GWO, a plot depiction of total wind-flow, is firmly in a -ve inertia state taking both the tropics and extra tropics as a whole.

 

A disconnect is evident between both components - with westerly wind additions (orange shaded) in the tropics across the Indian ocean as measured by inflection of wind-flow frictional torque at the same time as being over compensated by anomalous -ve inertia across mid latitudes and a large vacuum evident as a result of this c/o -ve mountain torques across both Americas.

This vacuum, in order to be filled, has been driving an extended period of mid latitude retrogressive sequences of anticyclonic wave breaking (blue shading on MT plots) and hence the sustained elongated blocked pattern across the mid hemisphere. At the same time the polar jet is energised across the northern perimeter of these blocking structures in association with added assistance of downwelling of +ve zonal winds from the stratosphere into the tropospheric boundary layers.

The MJO tropical component continues to operate at amplitude (in accordance with a prediction of recurrence periodicity cycle made back in early December).  The complex relationship this winter between the stratosphere & troposphere makes it problematic ascertaining how eastward movement of amplitude tropical convection through the tropics propagates into the extra tropics and then how directional flux of AAM anomalies routes the amplifying wind eddies either poleward in association with weakening stratospheric vortex, or continued equatorward ( as in Feb 2019 following vortex destabilisation)

Rising AAM under equatorward flux would give rise to anomalous blocking structures across mainland Europe set against a highly amplified recurving jet stream around a deep upper trough in the Atlantic. In such a situation continued disconnect between the troposphere (equatorward flux) and an unstable stratosphere would lead to the negating of potential outcomes of cold air advection.  The Hadley/ferrel cell fuelling a strong +ve NAO signature disconnect to a likely displaced -ve AO vortex, as mused about in the post under response.

At present, it is still early in February of course,  I agree that there is no real evidence to suggest that a poleward stratospheric pathway to work in tandem with a weakened vortex will inevitably occur & give the QTR that the UK members of this thread hope for to fulfill cold weather & snow aspirations..

[Mike Poole]

21 minutes ago, bluearmy said:

Gfs op shows what the fall out could be be reversal with flow in the lower strat and trop. No westerly momentum left to push down into the last third of feb  

Today                                                             Day 16 

      

Yes, that’s very clear, whether the trop plays ball after that, we will have to wait and see.  71% of 6z GEFS go for a SSW - and, notably, all the (higher resolution) op runs have had a reversal for some runs now, so hopeful that this time it will actually occur.  Best not to count chickens yet though!

2 hours ago, Met4Cast said:

So.. end of Feb/early March at the earliest, if we even see impacts from any potential SSW. 

It’s not the magical path to certain cold many seem to believe it to be. 

You make this point, or one similar, often.  I see no evidence that anyone on this forum regards a SSW as a magical path to certain cold!  I’d go further and say there are no magical paths to certain cold for the UK.  What we can say is that a SSW does shuffle the pack, with a few extra aces in there - after that, it is luck of the draw.  But - usually - that by itself gives us a greater chance of a cold evolution than the status quo, which as we know for the UK is often dire for cold chances.  

Agree last week in Feb is the earliest we would see impacts, though.  

[bluearmy]

12z gfs stretches the spv to the extent that it splits day 15/16 - a good split if we saw it imprinted in the trop but we do need to see some evidence that this might happen late feb rather than the disconnect that is evident on the cross sectional gfs charts of late 

[feb1991blizzard]

17 minutes ago, bluearmy said:

12z gfs stretches the spv to the extent that it splits day 15/16 - a good split if we saw it imprinted in the trop but we do need to see some evidence that this might happen late feb rather than the disconnect that is evident on the cross sectional gfs charts of late 

here's that aforementioned chart.

[Weather-history]

"February fill dyke"

Could be a very dry February for numerous locations. 

[danm]

3 hours ago, Mike Poole said:

 

You make this point, or one similar, often.  I see no evidence that anyone on this forum regards a SSW as a magical path to certain cold!  I’d go further and say there are no magical paths to certain cold for the UK.  What we can say is that a SSW does shuffle the pack, with a few extra aces in there - after that, it is luck of the draw.  But - usually - that by itself gives us a greater chance of a cold evolution than the status quo, which as we know for the UK is often dire for cold chances.  

Agree last week in Feb is the earliest we would see impacts, though.  

Agree. It’s a bit of a straw man argument. As you say, I don’t think anyone has suggested a SSW is a guarantor of UK deep cold and snow. It merely provides us with more tickets in the raffle and an increased chance of something wintry. Likewise the MJO. 

Edited February 5, 2023 by danm

[chris55]

I can foresee another cold and dry spring. These Strat forecasts will no doubt eventually filter down. The question is can we get the easterlies to filter down in time for some decent wintry conditions at the end of winter/early spring. 

 

[minus10]

...well the 12z gfes continuing to trend mild...just look at the milder gap between the mean and long term mean...the op...well....

[Stuie]

Put whatever weather you like to 1 side, at this time of year, it is remarkable how we have stopped the Atlantic for what seems like years.

 

[SLEETY]

24 minutes ago, minus10 said:

...well the 12z gfes continuing to trend mild...just look at the milder gap between the mean and long term mean...the op...well....

yet  a few days ago it was trending frigid in the ensembles.what a complete junk of a model,as mentioned before just chuck it in the Ocean

[Ali1977]

14 minutes ago, Stuie W said:

Put whatever weather you like to 1 side, at this time of year, it is remarkable how we have stopped the Atlantic for what seems like years.

 

It’s having a go at day 9 though, we need to trigger a change 

[ItNeverSnowsInWindsor]

6 minutes ago, Ali1977 said:

It’s having a go at day 9 though, we need to trigger a change 

We need polar vortex disruption!

[Daniel*]

I’d have little confidence in what GFS/GEFS is showing at moment the model seems to have love affair with high pressure, ECM now getting quite consistent in developing more colder fluid pattern.

 

[Guest]

22 minutes ago, SLEETY said:

yet  a few days ago it was trending frigid in the ensembles.what a complete junk of a model,as mentioned before just chuck it in the Ocean

How silly, it was really only the GFS Det for a couple of days and a handful of its ensembles that supported the idea of the really cold conditions, the mean never went cold and a milder Euro was always a decent shout. 

While not fully out the winter woods yet with ensemble charts like this it won't be long until I'm fully out of my dark season model hibernation. 

 

[minus10]

14 minutes ago, Ali1977 said:

It’s having a go at day 9 though, we need to trigger a change 

I'll try.....

[Stuie]

19 minutes ago, Ali1977 said:

It’s having a go at day 9 though, we need to trigger a change 

My post was in general, not predicting whatever comes next. Starting to forget what rain is down here in the South, that I find remarkable.