Model Output Discussion - Spring Has Sprung

[northwestsnow]

GFS ️

EC

Hopefully EC an outlier ..

Nope, mean is pants.. 

Edited February 14 by northwestsnow

[mountain shadow]

 northwestsnow The former drops the Iberian heights whilst the latter maintains the Iberian Desert High at 1030mb.

Only one winner.

San Sebastian up to 22 degrees tomorrow.

Edited February 14 by mountain shadow

[northwestsnow]

 mountain shadow shame because a cold north westerly suits us both ..and that would be some sort of bonus at the end of winter..

[Chesil View]

It's  frustrating being stuck in this holding pattern waiting for possible ssw fallout at the end of the month and into March while the modelling waxes and wanes as to how that may play out.

[Met4Cast]

This up-coming SSW does appear to be strongly linked to the MJO & associated +MT events, particularly the East Asian Mountain Torque. A paper from, Balwin & Dunkerton 1992 titled "Stratospheric variability has important implications for surface climate" seems to suggest greater forecast accuracy of SSW events following MJO orbits through phases 6/7.

We've been in a slow meandering phase 7 for a little while now but the previous eastwards progression into the Pacific triggered a (albeit quite weak) +FT event, the slow phase 6/7 has helped to amplify MT quite significantly & more prolonged than the initial +FT would have led you to believe.

This strong & sustained +EAMT has allowed for continued heatflux to deflect upwards into the stratosphere, unsurprisingly originating from the Himalayas (and to some extent N American mountain ranges) as per the first strat observe chart attached below.

What comes next in terms of predicting future weather is quite difficult. AAM anomalies continue to flux equatorward so despite a likely SSW & continued forcing from the MJO on the face of it suggesting high latitude blocking I'm still not convinced there'll be enough "oomph" to transition from an Atlantic ridge to a Greenland ridge.

I'm of the opinion that the late February cold weather will be more transient in nature, snow risks across N hills, perhaps along the N boundary of low pressure systems but by and large nothing out of the ordinary or exceptional, southern England once again probably struggling but determining the cold/mild boundary at this range is virtually impossible. Deep Scandi trough > Semi amplified Atlantic ridge seems the best bet currently. Colder than of late certainly, but widespread snowfall? Low likelihood from me currently.

[Blessed Weather]

A SSW not entirely in the bag yet. The latest GEFS 0z mean forecast (blue line) barely reaching a reversal around the 19th Feb before mean zonal winds recovering:

The members going for a reversal has fallen away from a peak of 87% earlier this week. At this stage not a favourable trend:

The SSW probability in GEFS is: 61%

Source: Weather is Cool: http://weatheriscool.com/

Yesterday's 0z 10hPa minimaps from Zac Lawrence (awaiting this morning's update) showed no members going for a split; so very much looking like a displacement event. This for the 20th Feb:

Source: https://www.stratobserve.com/ens_ell_minis

A displacement event not surprising given it's Wave 1 forcing:

Edit: Lots of info & reading about SSWs to be found in the Netweather  Research library :
https://community.netweather.tv/learning/research/stratosphere-sudden-stratospheric-warming-ssw-r54/

[Mike Poole]

Clusters this morning, T192-T240:

All clusters bar 5 have a northerly component to the flow by T240.  Cluster 2 looks the most pronounced with a well placed ridge and trough.  

T264+:

Clusters 1 and 4 develop a decent block, but it is not perhaps as far north as we would need for a significant cold spell, but both have promise.  Clusters 2 and 3 look like more transient ridging.  Still no obvious horse to back at this range!

Edited February 14 by Mike Poole

[Stephen W]

@Blessed Weather

Yes, I’ve been following these SSW charts all week and this morning’s update is not a positive trend. Some talk on twitter about a possible double dip SSW but that does not seem to be reflected within these charts. I’m no expert in this area so defer to those more knowledgeable. I think we are all hanging in the last chance saloon because of this potential SSW…

Edited February 14 by Stephen W

[bluearmy]

 Blessed Weather

yes - the tech reversal at 10 hpa 60N is looking brief and doesn’t get much below 10 hpa at that latitude

 

however, it you look at the wider picture, it’s a large reversal 

 

and the gfs00z op still has a sig area of reversed flow by day 13

 

the direction of travel on the movement of the spv fits with an active Atlantic feeding systems into a broad sceuro trough.  Possibilities for some wintriness but no sign of any deeply cold 850’s.  Elevation could do quite well. 

It does look like a split/displacement hybrid with the split v short lived indeed at 10 hpa whilst in the mid strat it is very evident and lasts a couple days.  The fairly rapid rejoining of the split looks to be responsible for the Atlantic jet strength and the upcoming nw euro trough.

the reversal up top due to arrive later today - not sure when it will be incorporated into the starting data but always worth looking out for any subtle changes once that has happened. The nwp should  have this by now though and over the past few days the drift towards the nw euro trough would seem to be the ‘’surprise’  that this reversal has delivered 

 

Edited February 14 by bluearmy

[minus10]

Difference between gfs0z and ecm at day 10 quite telling...

..looking at the jet you can clearly see the less amplified ecm..

...you kind of just know dont you....

[Cambrian]

Both the EPS and GEFS have moved away from the idea of a strong Scandinavian / NW Russian trough being established at around day 8. 

Comparing charts for the 22nd, at day 10 from Monday and day 8 from today’s 0z runs. 

EPS 

 

GEFS

 

Both suites appear to have underplayed the Atlantic troughing, both immediately to our northwest and upstream towards NE Canada. 

GEFS has been overplaying heights rises at day 10 further north in the Atlantic and through Greenland. EPS did a better job of those at day 10, but overplayed the heights through Western Europe.

Inter-model convergence, along with loss of wide ensemble spread, is a good indicator of the point at which these models become more reliable. This appears to be at around day 8 for this particular period. 

Both models have adjusted upward the activity of the Atlantic jet stream, and both would now seem to be indicating a spell of a NW-SE aligned jet stream running south of the UK and Ireland and down into Europe, around the base of a trough around Iceland. Day 8 GEFS. 

 

The overall take on looking forward from there at day 8 through to the last week of the month fits nicely with the ideas on the strat and the clusters.

For me, possibly a bit more to play for in the event than looks firmly on the cards at the moment. 

Rather cold and changeable for northwest Europe, scope for systems that develop over Greenland wrapped up in cold air, to run down the western flank of the trough. These feeds typically contain pockets of colder and less cold air, as systems pass through. It’s not a bad time of the year for some wintry episodes from that quarter.

I’ll be keeping an eye on how cold the lows heading out of Greenland will be, some wintry weather at times from this setup looks a fair possibility, and definitely more so than for the month up until now!

[ANYWEATHER]

The writing on the wall for winter has been there for quite a while now, and this morning we are hammering the last nail in the coffin in my opinion.  The SSW, won't have any implications for winter ,maybe Spring, but far too much emphasis on this phenomenon for my liking. The Atlantic appears to be king once again  in the days ahead ,with brief  ridges in between.

[Blessed Weather]

9 minutes ago, ANYWEATHER said:

The SSW, won't have any implications for winter ,maybe Spring, but far too much emphasis on this phenomenon for my liking.

You are most entitled to your opinion. Whilst there's no guarantee that a SSW will impact our little island favourably it's widely accepted that the occurrence of one can result in some of the UK's most severe winter weather, hence the interest in their occurrence. If you're looking for cold at least it's a ticket for the draw. This from the Met Office:

"In recent years some extreme cold, winter snow events have all been connected to the surface effects of sudden stratospheric warmings, such as those in 2009-10, 2013, and ‘the beast from the east’ in 2018."
Link: https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/wind/sudden-stratospheric-warming

 

[TEITS]

 ANYWEATHER The problem why too much emphasis is placed on a SSW is because of the wrong assumption that it means a cold, blocking spell of weather is going to occur. We should view it as being just one variable amongst many others.

My limited knowledge of a SSW is the chance this could displace or split the PV. Such an impact on the PV means all the cold air bottled in the Arctic could spill into Europe, N America etc. The main problem as I see it is the prediction of how a SSW will impact the PV and where this Arctic air mass is displaced to is poorly understood. You then have the added complication of how other teleconnections will interact with this warming. If this isn't enough to confuse everyone you then have the "unknown variable" that is making forecasting even more difficult.

Obviously we shouldn't give up trying to understand but never view a variable in insolation. This is why I suggest to many to view all the available data i.e Forecast models, ensembles, seasonal models, Met O LRF etc.

The other problem with forecasting is having a bias affecting your judgement. I'm not mentioning any names but over in the US we have someone who always seems to be predicting the destruction of the PV due to a SSW, every winter predicting a tanking AO and cold spells for either the US or Europe. However upon closer inspection this person is just like us i.e massive fan of snowy weather.

This is why without being rude to other members I especially take note of Tamara's posts. Being she made the wise move of leaving the UK I know her opinion is 100% based on science and 0% based on bias.

[Rain All Night]

12 hours ago, Rain All Night said:

12z deterministic runs, Wed 14th to Tue 20th (day 7)

I don't think I've learned anything new at all from this afternoon's deterministic runs. We see the big purple blob forming to the south of Greenland by day 7, which the ensembles have been suggesting may end up traversing over to our eastern side later on.

12z ensemble means, Wed 14th to Wed 28th (day 15)

And here we see that blob heading east from 21st Feb (day 8), though it is now not until around 26th Feb (day 13) that we see much of a trough to our east on the ECM and GFS ensemble means. Pressure seems to recover from the southwest after the blob has passed through.

Here is ECM ensemble member 46, which offers an explanation for what's happening between days 8 and 13 that I think is rather elegant:

0z deterministic runs, Wed 14th to Wed 21st (day 7)

Very little new to say as we watch the big purple blob approach... heights put up a little bit more of a fight on ECM than on GFS.

0z ensemble means, Wed 14th to Thu 29th (day 15)

The big purple blob arrives on our shores on 21st (GFS) / 22nd (ECM) Feb. GFS has it produce a deeper low height anomaly into Europe than ECM.

The Atlantic ridge / Scandi trough signal that we had been seeing originally then duly arrives from around 26th Feb (day 12), but it doesn't stick around for long.

Strictly just for fun, the ECM control run offers an illustration of what could lie behind the ensemble mean...

[Eagle Eye]

Despite the Greenland high regime not being favourable for we did get one and we did get a win for the teleconnections. This was from my post back on January 12th. 

"So we get another seperate jet situation w/favourably kinematics for the high just south of the Caribbean to be forced up again eventually as the momentum forces itself from jet to poleward forcing and so a mid-Atlantic block and/or a Greenland high is very possible"

"The CFS weekly is showing the southern disconnected jet and the slow southern descent of - VE zonal wind anomalies into the 2nd week of February ish, hence the Greenland high support increases. " 

Yes I used the CFS but only to get the timing right and it worked. It's a shame it wasn't helpful for us but predicting if it'll be helpful is a whole other ball park because then that relies on predicting the strength of it, working out support for a Euro high etc. The momentum to poleward forcing wasn't really enough to gain a strong Greenland high, it was just more of a weakened Greenland vortex area. 

However, if you think you can dismiss teleconnections then you're wrong, in fact, whilst it wasn't what we wanted it did become slightly favourable for us as we got some snow for the north. If you're expecting teleconnections to get it within 100s of miles months away you're wrong. 

With that said, we continue to run out of time on the chase for Winter, the MJO is going back into it's shell as it re enters a surpressed phase w/the drier air distributed by the changing IOD pattern into the phase 8 area. Along w/that AAM is doing what it's supposed to but it's just not being forced poleward, so we're stuck w/out much momentum and so we're relying on transient events which could well happen and have been shown on the models but they can easily be thrown out of kilter. 

[Weatherman_93]

Could be up to 16c tomorrow. None of you guys 'excited' about this?

[Chesil View]

 Weatherman_93

It really isn't that unusual for  temps to hit 16c with a longfetch southerly or south-westerly in February.  Not common I grant you but not that unusual.  we have already  hit 15.9 on 3rd.

Edited February 14 by Chesil View

[sundog]

 Weatherman_93 yet more above average temperatures.  Boring rather then exciting. 

[Nick2373]

 Weatherman_93 ? 13c max south feeling like 10c in the wind 

[Aiden2012]

 Weatherman_93  no absolutely not 

[Met4Cast]

On 09/02/2024 at 19:25, Met4Cast said:

Teleconnections aren’t providing much in the way of clarity either, equatorward fluxing of AAM anomalies are I suspect, helping to strengthen/maintain heights to the south of the UK whilst MJO through phases 7 & likely into weak amplitude 8 suggests blocking of the higher latitude type, two evidently opposing signals & an occasion when the tropics & sub tropics are not aligned towards the same potential outcomes, i.e opposing signals playing havoc with both NWP modelling & our ability to forecast in the medium-extended range with any clarity or confidence. 

A potential SSW in the mix too only further complicates the picture. I think getting cold into the UK is going to be difficult, particularly further south and particularly during February. 

I just want to go back to this post last Friday & indeed much of this is now coming home to roost within NWP modelling. If you're on a northern hill there's a good chance you'll see some snowfall next week as a deep trough slides SEwards with a little amplification of the Azores high following behind, not much luck for those further south though.

The SSW has trended more towards a displacement event vs what had previously looked like a split event and as such, I'm not sure how much hope we can have on this being able to overcome other drivers (discussed in the quoted extract above)

A perfect example, if ever, that taking the MJO in isolation & not in the context of broader windflow budgets often doesn't produce the desired outcome.

[Chesil View]

 TEITS

Very true Teits.  I think part of the problem is that SSW and the strat has moved into the simplistic media world added to this that we have had two gold standard ssw responses in the relatively recent past Dec 2010 and feb/march 2018. The former providing the coldest Dec in a hundred years and the latter the coldest such spell at thst time of year since 1845 and it is easy to see how everyone gets carried away. Add into the mix biased twitter based commentators and the hype just increases.

Even the oft quoted 66% figure bringing cold to the UK is I feel somwhat disengenuous as a dumping of snow on the usual suspects in Scotland  and Northern High ground in England can be classed as bringing cold and snow to the UK.

For me the test of a cold spell (and  this is honestly not just because of my location) is if a cold outbreak brings deep cold and /or snow to lowland southern England because then it is out of the ordinary  and beyond the realm of  a bog standard chilly outbreak with snow on high ground in the usual places.

As you say Tamara's unbiased posts that are made with out a required emotional outcome are valuable in keeping ones feet on the ground although even here Tamara's suggested shuffling hieghts scenario has not really come to fruition either and I say that with greatest of respect because it simply goes to show how ultra sensitive our uk based outcomes are to small changes in the background drivers.

Edited February 14 by Chesil View

[knocker]

 Weatherman_93 That's a bit like expecting a vegetarian to salivate over a fillet steak

[Eagle Eye]

 Chesil View

To be fair to Tamara she's not infallible, even the professionals did seem to think the cold could well occur. It's just been one of those Winters hasnt it.