Model discussion highlights

[Cambrian]

GEM has put in a decent shift today. The 12z ensemble mean keeps the faith with steps in the right direction between days 10 and 15. Part of the loss of Canadian lobe PV strength is undoubtedly due to the greater fuzziness involved with working the mean of the greater spread observed as time goes by, but that is still a sharp loss, along with a northward movement of the core.

Day 10

  

Day 15

  

The movement south of lower heights across Europe is also clear. Even the mean uppers show a marked drop, across the UK and Ireland, and well down south into Europe, a lot of cold beginning to slip down off the pole.

All a long way off for the numerical models, and the signal by no means properly cold (yet), but pleasingly, the timing of the loss of low heights over Southern Greenland shown on the mean anomaly for around the 24th is bang on with the formidable signal for Atlantic ridging in tonight’s ECM weather regimes forecast (that’s a lot of purple!), which is then largely blocked thereafter, so positive signs beginning to appear for some interesting times to come over the next few weeks heading into March. 

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804166

[Eagle Eye]

Found a good chapter of Simon Lee's thesis to compare to now and hopefully help with the forecasting effects of the likely SSW. Given the pre-SSW driving AWB North Atlantic-Scandi this is strikingly similar to that chapter

We're in a good position with this attack on the Vortex here though to displace the main barotropic stability driven towards Scandi-Russia in part with the Ekman velocity support not completely breaking the Vortex.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4803902

[MattH]

 

This may well 'leave a mark' looking ahead! - As a few have mentioned of late the tropospheric and stratospheric connection which could be made as a result of the SSW and the MJO really does signal the possibility of signficant interest for winter synoptics in late Feb and Mar.

As ever some would argue it's all too late and delays spring etc, but putting mild and cold biases aside after what has been a heck of a benign (boring, depending on your viewpoint) winter, overall, the atmosphere is about to get quite the 'shake up' and that can only bring interest from all angles and also provides another learning curve given how these variables will play out and interact with each other. 

As ever this doesn't guarantee cold or another BFTE but it sure does spike interest for significantly increasing the risk of producing some wild synoptics down the line. 

Cheers. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804256

[Tamara]

17 hours ago, Kirkcaldy Weather said:

Sometimes the transition into the associated composite patterns takes a bit longer to come to fruition (can also be a bit quicker) and with the corresponding cyclone developments in the Indian Ocean which are the phase 2 and 3 locations definitely suggests to me that it is indeed those phases rather than the 4-8 phase patterns which will be a focus following the blocking development

1 hour ago, The Weather Watcher said:

If it doesn't guarantee anything, then why is it even of benefit to discuss at this stage....until the effects are "laid out a bit clearer"? 

Just seems to me like an SSW is really just a pattern breaker, there are lots of those in different aspects of meteorology. Telling me the weather pattern is going to change in 2-3 weeks? Hardly wizardry on an island like ours.

I have taken these two posts purely as snapshots of two sides of the same thing in respect of context for use of teleconnections and stratospheric phenomenon and in respect of having altered quite appreciably my approach to them as more experience of them has been gained. The more understanding one gets, the more realisation there is that there is no room for bias confirmation in their use. Which admittedly makes it hard to provide worthwhile contributions into this thread that do not fit in with that purpose.

Apologies for repetition - but as I have commented many times the total atmospheric wind-flow budget, incorporating the extra tropics has to additionally be considered and then a further diagnostic of directional flux of momentum transport identified to get a reflection of a probabilistic ranges of synoptic responses. There is no x+y= equation with these composites, ever more skewed by increasing numbers of extra variables (including climatic forcing). Gauging the extra tropical synoptic response based on the tropics as a stand alone is prone to error as these can and do sometimes work in disconnect. Much as they have done through sections of this winter.

The Global Wind Oscillation (GWO) incorporates both tropical & extra tropical wind-flow and using this in tandem with tropical convection forecast expectations gives a fuller and more reliable indication. That is, if they are used objectively and not to fit a desired pattern. 

Equatorward fluxing of AAM anomalies continues as a consideration in this last section of winter heading into Spring helping to consolidate the mid latitude blocking patterns and distinct polar jet - much as was seen in February 2019 when an earlier and stronger warming across the polar field was evident and there was no cold air advection response. Of course currently proceedings are ahead of such developments and it could indeed be the case that seasonal wavelength changes are ultimately an extra catalyst for the weakening of the polar vortex to switch fluxing of momentum poleward and change the blocking pattern and alter the Northern Annular Mode state - but too many uncertainties remain about this. Those in more northern parts of Europe wanting Spring proper will be hoping that such a switch is not the case.. Some down here after an anomalously cold few weeks (on the southern flank of the mid latitude blocking) look for more seasonally normal temperatures and would welcome some extra rain (not a monsoon!) ahead of the scorching summer to top up from the very wet December c/o the -ve NAO state back then. So mixed feeling exist in different ways.

But irrespective of preferences (whatever they may be), it is wholly a large part of following the subject of meteorology to point to pattern changes ahead -  as interactions stemming from the tropics into the extra tropics are a bellweather indicator for changes ahead within the troposphere at the same time as zonal wind anomalies drop sharply across the polar field c/o substantive warming of the stratosphere occur. However, equally prudent to be open minded to precisely what synoptic outcomes might be across a wide expanse of the Northern Hemisphere. When expectations are geared so strongly in one direction in this thread at this time of year, the latter part is clearly a struggle to achieve.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804320

[Nick F]

32 minutes ago, Tills said:

 

I came on here to see what the models outputs are showing us for the last two weeks of winter.

So I have a genuine question.

Is this truly a model output discussion thread?

Or is it a teleconnection SSW thread seeking upstream signals that might [possibly] affect our weather some time in the distant future?

xx

I guess if there is something of interest happening in the troposphere, where our weather happens, there'd be more chat about what the models are showing for mslp/500 hPa for the next 15 days

But, alas,  there is very little of interest showing from all models at the moment, hence why a lot of posters are talking about the imminent strat reversal, of which is looking 100% likely, and its possible effects, in tandem with possible upper flow amplification from MJO reaching the western Pacific later this month, on the troposphere.

We are still some way off the models responding to these two drivers which may force a big change to upper patterns, given the reversal will take a few week to work down and the 10 day lag of the MJO, we may have to be patient until we see more interesting output from the NWP in the trop.

At least, for now, GFS is showing the reversal remaining longer-term high up, but it looks like it may take a while to work down at 60N, but perhaps will be quicker at high latitudes.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804257

[Cambrian]

I’ve been looking at the mean sea level pressure weekly anomalies for the next 6 weeks from ECM. I’ve come to enjoy these of late, and I particularly like the look of this instalment. As we’d expect, they fit in nicely with the weather regimes forecast and are a great place for us to be as we await the tropospheric effects of the SSW event.

Week 1 - European high; Week 2 - Atlantic ridge;

 

Weeks 3/4 - progressively lower heights from Southern Europe and heights building over Northern Scandinavia through Svalbard to Greenland.

 

Weeks 5/6 - northern heights become focussed on the Greenland / Iceland area, while the continuing lowering of heights across Europe through March is a real shocker!

  

This suggests that the reduction in the blocking (red) signal on the regimes chart is most likely only due to the encroachment of lower heights through Europe, fitting with the slack being picked up by the increasing NAO- signal, with a continued suppressed NAO+ signal as we head through to mid-March.

These charts are of course to be taken with a generous pinch of salt as usual because of their extended range, and in this instance additionally because of the potential variability introduced by the SSW itself, but at this stage it does look favourable for the main PV-related trough to drop into Europe with this SSW and that there is a signal for some very interesting and sustained pressure anomalies already in place. 

If we have felt that the Atlantic has been relatively docile this winter (no named storms, etc.), then the charts for weeks 1-3 look to be taking that to a whole new level. Any ocean-driven action even thereafter appears to be well to our south. 

It looks like another protracted period of slow-moving weather, with the UK and Ireland on the northern side of the Atlantic jet stream, scope for northerly winds by week 2 and a predisposition to easterly winds by week 4,

 

potentially for several weeks through March, increasingly unsettled (though not at all mobile) as low pressure pushes up from the south and southwest, and even if not landing anything that extreme from flying PV debris, in any case a more than likely cold end to winter and very slow start to spring. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804333

[mushymanrob]

1 hour ago, Astral Goat Juice said:

 

That being said, studies have shown that early winter SSW events tend to bring cold temperatures to the UK, while later winter SSW events are more likely to bring milder temperatures.

Sorry but i disagree with that.

Since 1958 when SSWs were first recorded there have been 13 SSWs in February, only 3 were not followed up by some cold Wintry event. 2018 and 2013 were extreme examples, most post SSW events in Spring were short sharp events.
Cold spells in Spring are common, but the data suggests that a SSW Spring is likely to produce a more severe spell than a non SSW Spring with "normal" cold.

I used the SSW database and Bonacina snow database alongside archive charts for this research.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804371

[Mike Poole]

One thing that is becoming increasingly clear about this event in the strat is its longevity, in terms of the reversal of winds.  GFS 12z shows this quite clearly:

The effects could therefore last quite a long time.  It will be a couple of weeks from the event before we see anything notable affecting our weather, but there are initial signals appearing on the models on the day 15 timescale now.  The placement of the strat vortex and ridge continue to look in the right ballpark (T384) so I’m slightly more than cautiously optimistic on this one:

It is always a great learning opportunity when a SSW comes round (there aren’t that many of them, ~6 per decade) so fascinating to watch it unfold…

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804414

[Eagle Eye]

Here's a lot of information about SSW's with the 2018 February looked at via Simon Lee's PhD thesis. Linked here and press the text to download on phone and open on computer, making sure that it's the University of Reading site with the badge being in the top left corner just in case I've accidentally linked the wrong thing here;

Stratosphere-troposphere coupling on subseasonal timescales - CentAUR

DOI.ORG

---

University Publications

"one of the S2S model forecasts issued at the time indicated a major SSW until early February"

So though the subseasonal to seasonal predictions suggested increased chance of a SSW with the persistence of the Ural block (similar to this year though it tended to be a bit stronger) and Aleutian low (we've struggled with that a bit more this year) perhaps they struggled to forecast the wavebreaking very well in the mid-term and Stratospheric forecasts tend to try and stabilise the Vortex quicker than normal in my opinion and in no way forecast the strength of planetary Wave breaking to a major degree of accuracy. So despite the Stratosphere being forecast better than the Troposphere generally, when the Trop-Strat connect Wavenumber is between Wave-1 to Wave-2 with Wave-1 favoured on forecasts I find, then Wave-2 can be downplayed making the forecasts tend to favour a minor SSW.

"S2S model forecasts abruptly transitioned from projecting a strong SPV to a weak SPV/major SSW in late January-early February"

Models tend to transition quite quickly given that in a lot of SSW's, with wavebreaking the thermal gradient really helps with the creation of stronger planetary wave transitions and the oscillatory nature of PJO (polar-night jet oscillation) events with a strong polar vortex. So a more fluctuation in vortex strength Trop-Strat with the characterisation of eddies Trop-Strat link upwards and downwelling of westerly/easterly winds in anomalous vortex events. So a strong polar-night jet especially in Nino years may be overcome better than you would think though Nina years with less flux in eddies is fairly unlikely to be much chance of a SSW though the way that the atmosphere is acting is more important in short-term vortex flux than the oceanic variable unless they're linking up well in terms of convectively coupled kelvin waves (CCKW) and so there's less long-term wave variation.

"showed a strong relationship between the accuracy of stratospheric wind forecasts and the intensity of an anticyclone over the Urals (named the ‘Ural high’)"

Clearly the differences in the strength of the wavebreak pre-cursor structure and strength is a big effect on the Stratospheric predictability. The repeating Ural high this winter was bound to have the effect of fluctuating verification of Stratospheric forecasts as it is one the main roles along with the Alaskan high to eddy driving Trop up to Strat. I prefer the Ural high - Aleutian low setup as a good Wave-1 setup as the rotary wavebreaking where the vortex undercuts into the Europe-Russia area so the westerlies suppress northern advancement of the Euro high and support blocking to the west.

“They implicated tropospheric systems over the North Atlantic and subtropical wave breaking; forecasting experiments showed a realistic SSW only occurred when a North Atlantic weather system was correctly represented in the model.”

This is important to note as North Atlantic anticyclonic wavebreaking (AWB) occurred recently as shown below and also the minor role of rapid cyclogenesis off the eastern seaboard for upwards wave flux building with planetary wave vertical movement. Before wavebreaking over the next few days in the Strat which imparts the strong enough easterly force via the usage of potential vorticity lobes upon breaking and then the refraction of the wave towards the Greenland area as it anticyclonically breaks in the Stratosphere just like the Troposphere.

With the NAM in weak vortex events you can see the initial –VE NAM (it’s an odd colour scheme) linking up initially and eventually over time it downwells with a tripole of –VE NAM linking down to the surface initially over 7 days (likely due to the effects of any AWB before rather than the Strat reversal in and off itself) with the main effects being felt between 2-5 (ish) weeks later. I suspect given relatively weak upwards wave flux forecasted and the relative neutral NAM linking upwards we’ll see a relatively slow evolution though this may be sped up to just being in time for a short fetch to actually be able to deliver something. I wouldn’t call this a likely BFTE though but the timing between the SSW and the MJO Phase 6/7 may help bring the best chance since December.

In the S2S generalised model, the exchanges between the tropics to extractropics and AWB feedback recently it doss suggest the more blocked type of feedback loop. With the Scandi shifting pretty will linked with the further east US ridge and less amplification on both sides hence why we didn’t get a BFTE earlier this month.

Furthermore, a strong Scandi-Greenland dipole (we had Scandi-Ural for a time which is still good) is a very good sign and on average are followed by a weakened vortex. It highlights how relatively weak AWB pushing into some sort of high lat blocking (especially in the Greenland-Scandi area) even if its relatively weak will have larger responses as you go ahead in time and the further up you go. Making the Strat response to that Trop driver fairly significant. Sudden changes in the atmosphere via Trop wave breaking to high lat blocking helps cause sudden Strat changes which is important in not letting the Vortex recover quickly enough.

This makes Wave-breaking in the Trop a big driver for Strat variation as opposed to slower block evolution. Though of course that state of the Strat will change the response to the vertical Wave drive.

It is noted that:

"favourable stratospheric states can arise through ‘pre-
conditioning’ "

Suggesting that the warming and weakening that occurred earlier on in January has helped set up the Strat vortex accordingly. So two time transient Wave events are very good for setting up the Vortex for an AWB induced S-G dipole to vertically produce planetary Wavebreaking in the Strat especially at the all important 10hPa value.

This mechanism seems very good for driving Strat vortex sudden changes with the pre-conditioning via a Ural Block typically. The omega Ural block being a slower progessing event with weaker eddies it appears but still enough to displace the vortex which is good for another event coming along and keep helping make it barotropically unstable and closer towards baracolinicity with Ekman velocity away from vortex circulation. Essentially, we don't need as strong of a Wave-2 to cause a split and sometimes we won't even need a split for cold if the vortex displaced into the right place. 

Downwards coupling after this pattern;

The main response to a major SSW as has been said before is the negative NAM mode coupling downwards but there's a lot of regional variability based off different setups. With the Arctic high driving SSW and MJO Phase 6/7 movement you generally get the idea of a -VE NAO and that appears to be the most likely scenario under that criteria. So if we can get some downwards propagation of the SSW into the Trop then given the MJO movement I'm thinking that getting that Greenland high may be quite possible but in general any blocking to our north is quite possible and perhaps the setup we're about to go into is the best possible displacement setup for us.

A strikingly strong -VE NAM coupling downwards as long as upwards wave flux is good then I think an easterly in response is possible. Though I'm basing that off the MJO Phase 6-7 lag and SSW coupling downwards timing themselves well.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804432

[Cold Winter Night]

45 minutes ago, Mike Poole said:

One thing that is becoming increasingly clear about this event in the strat is its longevity, in terms of the reversal of winds.  GFS 12z shows this quite clearly:

The effects could therefore last quite a long time.  It will be a couple of weeks from the event before we see anything notable affecting our weather, but there are initial signals appearing on the models on the day 15 timescale now.

Those profiles show that the reversal is descending slowly, not making it anywhere near 500hPa yet.

Considering the lead time, that Euro and Atlantic High amplification that GFS, GEFS, and to a degree, EPS, are showing could IMO very well be more of a response to the phase 5 to 6 MJO progression.
With the MJO moving from 5 to 6 around February 12, and a 10 day delay, that would fit amplification starting around February 22/23.

Apart from a possible, but rare QTR, I think the first SSW effects may land at 500 hPa in the first week of March, some 15-20 days after the event.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804447

[nick sussex]

Just been looking at the February 2018 SSW date of reversal .

That occurred on the 12th so how well did the ECM do pre-reversal .

Heres the T192 hrs output on  the 11th 00hrs run.

Heres the T144 hrs output on the 13th 00hrs run post reversal .

Of course the other background signals might be different but it’s just an illustration that even though the reversal was imminent in the first chart how well did the op do as opposed to when the starting conditions include the reversal having taken place .

The post reversal days 7 to 10 were pretty accurate in getting the high and deep cold pool moving west .

So just something to bear in mind . We might not be expecting a QTR but with that caveat . Until the reversal actually happens we should treat the current outputs with some caution .

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804486

[Nick F]

Interesting chart posted on twitter this evening of composite height anomaly 0-30 days following SSW displacement events during La Nina since 1990.

Suggests N Atlantic and Greenland ridging and low heights over northern / northeastern Europe.

 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804500

[bluearmy]

7 minutes ago, Spah1 said:

Why are the ens run at a lower resolution?

Processing power 

but the new eps upgrade will take them to a pretty high resolution. We have discussed over the years if the ens should be run at a v high resolution. the ec op is noted as sometimes being too sensitive and a small change early on can create a feedback loop which generates way too progressive a pattern later on. If the eps go that way, they become less informative- this seems a counter intuitive view but plenty on here will know where I’m coming from. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804498

[Tamara]

51 minutes ago, Cymro said:

I must say the prospect of a severely cold March, as a vegetable grower, fills me with absolute dread! I'm hoping we see impacts from MJO potential reversals with SSW sooner rather than later so it can be done with before mid March! 

There remains all kinds of potential outcomes from the stratospheric diminution. This winter has seen a complex relationship between the troposphere and the stratosphere - I made some posts in late November foreseeing such complexities between the tropics and the pole. It has indeed panned out that way in respect of the differences between the earliest part of winter, and the countervailing forces which then flipped to a lot of equatorward fluxing of momentum. This has meant that active tropical forcing has manifested anomalous sub tropical anticyclones across the extra tropics rather than blocking at higher latitudes that *may* have continued to result from poleward fluxing of momentum transport.

This is a truncated background context, at least as I continue to see it, which frames the balance of events for the upcoming SSW period which is occurring as tropical convection propagates eastwards across the tropics.

Some comparisons have been made with February 2018. It is certainly true that the 2023 SSW is timed to occur close to when the 2018 event did - but the background relationships within the troposphere and the stratosphere are not the same as I see it. Winter 17/18, as a whole, saw an unstable wind-flow propagation coupled  relationship between the tropics & extra tropics. Equally, an equally unstable partitioning of zonal wind anomalies existed across the polar field which seemed primed to detonate as far back as mid January 2018.. In that sense the tropospheric synoptic patterns moved in symmetry with the machinations within the stratosphere. That is not the case this winter - there has been a stand-off between the two with the troposphere lead of early winter, overtaken by a more stable stratospheric lead.

Poleward momentum was very extreme ahead of the 2018 event with a massive surge of angular momentum tendency that led to a temporary reversal of the La Nina walker cell. Broadscale extra tropical mountain torque deflection of wind eddies from the troposphere c/o wholesale meltdown within the atmospheric circulation created the means for a quick tropospheric response from the SSW and -ve zonal winds at higher latitudes manifesting robust blocking structures.

The background this winter has differences - the Global Synoptic Dynamical modelling (GSDM) (which essentially is a diagnostic of the wind-flow budget through frictional & mountain torque mechanisms in the tropics & extra tropics) has been more stable than during the 17/18 winter. In simple terms, other than the very early part of winter, there has been equatorward rather than poleward fluxing of AAM anomalies - as outlined at the beginning of the post.  Whilst tropical forcing is active, the same as was the case in 17/18 - the different pattern of directional fluxing alongside a more stable stratospheric profile, overall, has dampened the amplification profile within the extra tropics. Hence limited poleward amplification of anticyclones that have been produced by the wave-breaking transferring from tropics > extra tropics.

These differences make predicting the outcomes this year ever more complex and uncertain. Much more so in my opinion that in February 2018 when probabilistic outcomes were more clear cut and loaded emphatically towards a QTR and anomalous polar blocking.  Following the huge +ve AAM rally of early February 2018, momentum collapsed in tandem with the timing of the SSW and this actually helped to augment the tropospheric reaction as attempts to switch jet stream inertia into the polar stream were utterly nullified by the wall of -ve zonal winds at the tropospheric boundary and this road blocking enhanced the cross polar ridging response and cold air advection processes.

This year, as stated, the lack of relative strength of momentum transport (more stable GSDM within the troposphere) means that there is less latent inertia to enhance/superimpose on any downwell of zonal winds into the troposphere that may occur. Indeed it is conceivable that equatorward flux could hinder processes and lead to either a supressed response, or a diffused response. 

Such a diffused response (if it was to occur) could also on the other hand be an extended one if seasonal wavelength changes into Spring re-configure synoptic responses with the troposphere (wavelengths evolve to enhance cold air advection processes more easily than during winter). A 'warm' polar stratosphere and 'cold' tropical stratosphere suggests enhanced Brewer Dobson circulation of ozone & continued promotion of active tropical convection - and this could play its part in how amplification processes within the extra tropics behave. Quite possibly, very differently to winter wavelengths based on evolvement finally to a coupled unstable tropospheric> stratospheric state. The difference being this occurs after the SSW rather than priming the atmosphere before it as occurred in 2018.

In summary, a lot of complexities & uncertainties and an open mind is required in the days (and weeks) ahead.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804685

[nick sussex]

I’ve found some further strat research with interesting conclusions .

Splits tend to have a more immediate trop response .

Displacements can take 1 to 2 weeks to show up in the trop .

There is less difference between the two types 3 to 4 weeks after the SSW .

Displacements tend to show greater temperature strat anomalies but both those and splits tend to show similar overall trop responses .

They also suggested that the MJO could effect the downward response to the trop .

The full research paper is called .

The Impact Of Split And Displacement Sudden Stratospheric Warmings On The Troposphere .

It was published in 2021 so quite a new piece of research.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804705

[phil nw.]

Good luck to you and yours Matt always enjoy your posts.I hope you can come back on here in time if you can.

Meanwhile looking at day 7 higher up at 10hPa in the stratosphere we can see 06z gfs and the last ecm chart from Berlin University pretty much agreeing on the current warming being across the pole by day 5 and the displacement of the spv.

 

We can see the reversal(easterly winds)across the pole as the core of the spv is pushed south.Now it's a case of waiting and watching to see if this reversal filters down and how it may affect the 500 pattern,which is the great unknown.

Only limited data available from Berlin but as Mike shows above signs that downwelling of the negative zonal winds are showing towards month end from the GFS suite.These from stratobserve.

These are forecasts at 100hPa the lowest Strat.level at day 10 and day 15

Indications of the pv heading towards Siberia and Atlantic ridging.It would be naughty of me to speculate that we could see an early March northerly.... 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804718

[Mike Poole]

A hint of the downwelling affecting the trop at the end of the GFS 6z this morning:

By the way, I don’t think we’re expecting the blue colours on the left chart (i.e. net easterly flow) to get down as far as 500 hPa, that would mean the weather in the troposphere as a whole flowing from east to west all the way round the globe on average, which I’m not sure is realistic.  (Does anyone have similar chart for 2018 once the downwelling had happened, because my recollection is that there was a flip to easterlies over thousands of miles, would be interesting to see how close it got to a net easterly at 500 hPa?)  We do need to get rid of the yellow colours though, and this run does that.

Meanwhile, it is worth keeping an eye on the MJO, the models may be underplaying the amplitude of this, as the two charts below show ECM take yesterday (left) and today (right):

You can see the data point for 10 Feb verified with more amplification than the model predicted, and therefore the greater amplitude in the further forecast from today’s plot.  Looks to me like we might see some benefit from both the MJO and SSW downwelling at about the same time, just before the turn of the month.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804714

[Nick F]

20 minutes ago, Mike Poole said:

I think if it was MJO it wouldn’t appear out of nowhere like that.  SSW effect, well we’re 4 days away from it now, we might expect the models to start to get to grips with all that the SSW entails, and make abrupt changes.  So my money’s on the SSW, vertical section of zonal winds plot later might give a clue?

Yeah maybe, we await the 12z GFS cross section on weatheriscool.com - but previous runs the downwelling of the reversal didn't appear to reach anywhere near the trop towards then.

The late Feb 2018 change in the trop that brought the BFTE not too dissimilar in area that +ve heights appeared over NE Atlantic up to Svalbard:

24th Feb 2018                                           12z GFS for Sun 26th

This was the 15th Feb 2018, note the strong TPV to the NW of UK like we're worried about in next few weeks:

Of course, we are dealing with a displacement this time, not a split like 2018, so I would expect it may take longer for a trop response to the sustained reversal way up and perhaps not as similar as 2018 response either, that's if high latitude blocking is the response!

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804817

[Eagle Eye]

@MATT TATTOO Wish you all the best and hope to see you here soon.

It's clear we're entering the SSW period now with the zonal winds already pushing down, now is the waiting game as we see what happens between the Strat and the Trop.

"The SPV is currently weaker than ERA5 average 
and is forecasted to remain weaker than average (according to GEFS-mean)
0 of 31 members have stronger vortex than average at the last forecast step (2023-02-26 06:00:00)

The SSW probability in GEFS is: 100%

The zonal mean zonal wind at 10 hPa 60N is today (GFS analysis): 13.2 m/s"

The setup for 10hPa appears to be better than 2019 though worse than 2018, it's sort of in the middle between the two making it almost a nail biting game to see if it can downwell properly.

I mean even 250 hPa whilst not reversing slowly loses the zonal wind speed strength though the Trop is of course handled worse than the Strat.

Oh and if anyone's interested, there's a Wave-2 event looking likely around the 25th which may or may not help with downwelling I'm not exactly sure.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804834

[Cambrian]

It’s clearly going to need a lot of southward-driven energy from the Arctic to shift the heights that look likely to give us a quiet, potentially pleasant spell (particularly further south) heading into next weekend, but the last couple of GFS operational runs have given it a good effort. 

As shown here on the 6z, it hinges on a low donated to Svalbard by the Canada / Greenland PV lobe at day 5,

 

the beginnings of a wider package of assistance that involves lower heights as well by day 8.

 

This sets up a trough pointed south down the Norwegian Sea towards us, that begins to punch a hole in the Euro-Atlantic heights.

This extension of lower heights eastward through Svalbard to Scandinavia is picked up in the ensemble means too, day 5 / day 8 here. 

 

By day 11, this develops into a splitting away of a chunk of PV to the Norwegian Sea / Scandinavia, opening the Arctic gate. Look at that energy running along the isobar track from eastern Siberia, all the way to the UK and Ireland, as that earlier extension of lower heights to Scandinavia hooks us in with it. The gap can be seen in the anomaly chart too, running from the Kara Sea through Svalbard to Iceland. Op, op anomaly, mean.

  

The orientation is different at this stage but there is good support from the day 11 mean for the lowering of heights and establishment of the Norwegian Sea / Scandinavia trough, so maybe just a hint that we could squeeze a few days of a colder flow from the north, before we perhaps get to something like this much more direct approach from the Canadian PV at the end of the run!

 

Good old GFS.

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804717

[Blessed Weather]

The GFS 10hPa temperature charts provide a visually stark illustration of what's happening to the sPV following the SSW. The first chart from early January showing a strong, well organised sPV, compared with the second chart for T384 28th Feb. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4804980

[Mike Poole]

ECM clusters starting to show more of a range of options in the extended period - this is also probably a good thing.  T264+:

Cluster 5 is what we should aspire to with a -NAO and Griceland high and easterly (day 13)!  Clusters 4 and 3 a good atlantic ridge, and cluster 1 headed that way too.  

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4805306

[Cambrian]

Today’s 0z ECM operational run at day 9 is showing more of the kind of northerly evolution for that period just going into the last week of the month that has appeared and disappeared across the models in recent days. 

First, here’s yesterday’s 0z run @240h

  

And today’s 0z @216h

  

The heights over the mid-Atlantic are completely transformed, from flat to strong amplification all the way up to southern Greenland. The surface high is a long way further north and west. 

As a result, by day 10 on today’s 0z op, we are in a properly cold air mass, heights pushing up towards Iceland. That little low to the west of Portugal is beginning to link up with the polar Scandinavian trough and the European heights are getting pushed southeast. 

  

That could easily develop from there into a cold northeasterly for the UK and Ireland, down the western flank of the long wave trough running down from Scandinavia to Iberia. With heights getting pushed up between Greenland and Iceland, and falling away in Europe, it’s potentially one heck of a setup as we await developments towards the end of the month. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4805391

[Cambrian]

12z GEM operational run through to day 10, in keeping with the strong Canadian PV lobe, yes. But another operational model to start playing with an uptick in the Siberian lobe from around day 3 or 4, and stronger Atlantic ridging from around day 7 resulting in the dropping of a trough down into Europe, the upper trough extending southwest to south of Iberia.

  

This trough is a bit further west than on the 0z ECM op, brings us into a northerly flow by day 9 with some cold uppers. PV still relatively strong at the end, but because of the stretching and formation of the two lobes, it doesn’t seem to preclude sufficient scope for amplification in the North Atlantic for a cold polar maritime / Arctic maritime influence from evolving in the models for next week. 

The cold air for us is clearly not happening on every model (GFS op?) and certainly not on every run of those where it has cropped up (12z ECM op?) but it’s definitely a theme and could well be worth keeping an eye on. 

More to the point, the recovery of the Siberian lobe and the appearance of the Scandinavian trough is commonplace across the output. 

12z GFS ensemble mean, day 7 vs. day 10….

 

And the T850s day 7 vs. day 10….

 

Just hints, I know, but plenty of them. 

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4805491

[Mike Poole]

ECM clusters showing more of an indication of a blocking signal this evening.  T192-T240:

Cluster 1, with 3 close behind, pushing up an atlantic ridge.

T264+:

Evolution towards northern blocking heading towards scandi now on the first 3, with the mobile cluster 4 having just 8 members.  

Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4805492