Model discussion highlights

[nick sussex]

There’s a lot going on !

No major drama this morning for coldies . The UKMO improves and the ECM seems to be developing a new pattern in its later output .

The GEFS zonal wind forecast has changed once again with the increase in westerlies delayed . This is supported by the NASA strat forecasts which are also now showing an extension to the downwelling .

So are we seeing the effects of the second strat reversal coming quickly after the one last month .

It certainly looks like the strat and trop are working in tandem .

Looking through the layers and latitude of the NASA charts . We see a brief pick up in the zonal flow 8th into 9th towards the pole then another reversal .

Not sure how often if ever the models have dealt with this type of rollercoaster for that reason I’d still be wary of the later output although blocking looks to continue to influence our weather .

The all important detail looks difficult to pin down .

Certainly an interesting period of weather coming up . We should though be realistic about what to expect . This isn’t the BFTE aka 2018 in the ten day timeframe in terms of set up ,we don’t have the depth of cold on offer and will need some luck with timing re snow falling and laying .

Cloud cover will make a difference and any snowmen will need to be built in shaded areas ! 

The ECM day ten does add a bit more interest if that was to develop further , possibly something from the ne or east later . Perhaps we could aim for mini BFTE . 

Anyway that’s well into FI . Overall an encouraging start for coldies . Let’s hope for continued improvements.

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4814896

[Singularity]

Bit of a trend afoot to hold the main Atlantic low further west toward D10 which allows part of the major blocking high to drift back toward Iceland.

Perhaps via interplay between a new round of lagged MJO phase 7 forcing (encourages high pressure over N Europe) and downwelling anomalies from the stratosphere that keep the AO negative and allow high pressure to locate further northwest than would usually be the case.

Given I’ve long been expecting main SSW impacts by the start of 3rd week March, this is concerning for those who’d prefer springlike weather - there could be a very long spell of well below normal temps (overall day & night combined). A chance of light winds and sunshine providing respite on some afternoons, though.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4814923

[nick sussex]

The lowest  ever March temp in the UK is -22.8 recorded on the 14th March 1958 at Logie Coldstone in Aberdeenshire .

The pattern was similar to the current forecast set up with low heights and a slack flow .

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4814990

[johnholmes]

My view on the upcoming weather with the 500 mb NOAA anomaly charts and the ECMWF 10 day output, charts following.

On the 6-10 chart the contour close to the Scottish border is quite cold, 534 DM, just look where it originates, then curling around the centre of the main trough centre.

The 8-14 is showing the westerly flow with any ridging/+ve heights well west. However check its contour height, 540DM and its origin, mid way up the Aleution islands. So not deep cold by this chart but hardly mild by any standard.

I would suggest a 4-5 maybe 6 day deepish cold then a rather cold surface weather for the whole of the UK. Colder throughout the further north one lives.

Looking at the ECMWF run of charts from 8 March, the UK loses the closest 850 mb charts around the 8th but the

-5 C remains over much of the UK until the 10 th when the Atlantic low is shown influencing most of the UK.

This looks to be a slightly different view of the cold spell but not too different allowing confirmation in my view of the comment above.

Obviously detail on any snowfall will be for the synoptic models to gradually come to a consensus of when/where and how much for any particular area. Possibly minor troughs giving snowfall not picked up by the models even at T+24 or less. Good viewing for coldies but not for those wanting a warmer spring to get going.

ECMWF charts

NOAA

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815054

[Nick F]

06z GFS doesn't pump the Iberian heights like the 00z EC  / EPS, then again the 00z GEFS mean doesn't either.

The heights tendency over Iberia in the medium range looks crucial to the longevity of the cold spell, too strong and greater risk of milder air flooding at least the south, some uncertainty in this area IMO. 

But at least one thing I've noticed in favour of prolonging the cold is the tendency for the trop PV to stay close to northeastern Europe on 06z GFS and 00z EC rather than bouncing back to Greenland as GFS was keen on previously, which makes sense - given the MJO going into high amplitude 8-1 and the continually drip down of the strat reversal following the SSW.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815002

[seabreeze86]

For all this about it being to warm is March etc 

This rather bog standard chart led to this at sea level on April the 11th 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815021

[Eagle Eye]

Essentially my view is that it is looking cold enough for snow to fall. Obviously for it to lay well that relies on other components that quite frankly I can't be bothered with at this range, the nitty gritty detail of sun angles and latent heat release is very technical and not just reliant on "Its March" as March is a very transitionary month in the first place. Plus it relies on good forecasts of cloud cover and everything like that.

The trouble with forecasting of boundary layer physics is that

1 - There is no clear line.

2 - Viscous forces dominate inertia forces in boundary layer fluids.

3 - Tangential shear stresses are therefore a big factor of wind flow for heating at boundary layers compared to the middle tropospheric layers where the flow tends to follow a more stable flux vector direction.

4 - Given the Coriolis force from the rotating Earth at boundary layers, wind tends to follow left of above geostrophic flow given surface drag components and low-layer stress on fluids increases .

5- IE internal friction of the atmosphere at lower levels stresses more compared to free flowing laminar baroclinicity of Eddy driven Troposphere weather. Increasing the viscosity.

6 - Resistance to surface layer deformation (viscosity) is therefore a big part of the physical structure of close to surface layers.

7 - Also meaning that low-level laminar flow can be influenced quite a lot by sub-grid gravity waves.

8 - That means that surface conditions are more chaotic than above.

9 - To cut a long story short this has nothing really to do with right now really but it does highlight the issue on surface forecasting beyond when models are capable of moderate scale gravity wave forecasting.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815088

[Mucka]

I still think the models are likely overplaying the Atlantics hand in the attempted breakdown on the 11th but we will see if that is reflected in the output over the next 48 hours.

The best day for snow chances before any breakdown attempt that could bring frontal snow will be the 7th as the Arctic trough digs SW.

GFS has low pressure developing over S of country as the bitter cold air from the NE meets milder Atlantic air coming up from the SW on the 7th.

UKMO has low embedded within the trough develop just to our E.

GFS is the snowier option and could give widespread snow whereas UKMO would pep up snow showers from the NE and drive them inland, 

UKMO/GFS 120h

 

The coldest temperatures will likely be on the 8th and 9th for any chance of local date records across England on those dates. A national minimum isn't likely and my original post alluded to potential date records for some locations in England. There are a lot of factors at play other than just cold air aloft here and it will require snow cover, clear skies and a col all of which may be in the forecast so we will wait and see.

Whatever happens the majority of people are likely to see snow falling at some stage before we welcome Spring so plenty to be excited about if you like that sort of thing.

 

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815242

[damianslaw]

Strong echos of what happened in the models in the lead up to the December cold spell, it was only as we approached the nearer timeframe 72-96 hrs that they began to ditch the idea of a shortlived wonder, and instead prolong the cold, this only happened really when the cold arrived on the 8th Dec, we are not there with this projected cold spell, but interesting to note how the GFS and ECM are holding the atlantic at bay out to the 10th/11th at least and there is a signal for heights to stick close to the north of the UK - and not retreat rapidly away to the NW.. just as happened in the December spell, on that occasion they did then swiftly move away, but we are in a very different set up, seasonal wavelengths, effect of the SSW this time around suggest the altantic will not get its way, and I would not at all be surprised if we end up back to square one very quickly after any attempted atlantic breakthrough, i.e. heights to the NW again.. as being indicated by some of the longer range models. 

A very interesting period of model watching ahead.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815272

[topo]

I don't see why March 10 is a problem for the UK regarding the sun angle..

Sure the sun is at a greater altitude than in December or January but UK is still north enough for a March sustained snow cover.

Actually the maximum sun altitude on 10th of March at Birmingham is the same as in New York on 6th of February and the same as in Nagano, Japan on 20th of January...

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815025

[Snowman.]

6 minutes ago, RainAllNight said:

When they go up and then right back down again, does that suggest that a "battleground low" has come through and the cold air has won the battle?

Most likely. If you go up the country you’ll find the cold line in which you’ll probably find a lot of snow as well!

Its super far out to take as gospel as these tend to change consistently and even at 48hrs out can still vary as much as a 100 miles or so. 
 

But the trend is clear for some kind of slider/channel low and the further south it is the more the UK stays cold. Best outcome is through the channel as it gives those south a snow event and allows those north to get some beefy showers as the wind changes direction. March 2013 is a classic example of this. 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815085

[Cambrian]

Focusing on the more reliable and the northerly for now then….which we will hopefully all enjoy - 

No intention to criticise here (not in my nature in any case) and I think the Met Office do a very difficult public-facing job brilliantly. I think they’ve got it broadly right with the forthcoming northerly pattern and it’s longevity, and with their own model too. 

However, there is one aspect of their narrative in which they continually get the emphasis wrong and that is the impression that they give in the run-up to wintry northerly spells that the south and west are likely to stay largely dry, frequently understating the scope for significant snowfall as a result. It gives an incorrect impression. In straightforward showery setups, a wiser term might be ‘away from north facing coasts’ or ‘away from places exposed to the northerly wind’.

Having said that, we live well inland and with the mountains of North Wales to our north and northwest and invariably get appreciable snow off a northerly (even a true northerly, let alone a north-northwesterly) that has set in for a few days. It happens time and time again. Pembrokeshire has its famous dangler, the same line often bringing Cornwall in to the frame for showers, not necessarily wintry, but certainly not dry. Troughs often form in the Bristol Channel that affect Devon and Somerset.

More substantial snowfall can occur from frontal systems, and small lows developing in the flow that form their own circulation, both of which back the wind northwesterly or westerly before they land in any case, with a lot of precipitation driven in from that direction, only straightening to a northerly again at the back edge when clearing.

From the current models:

12z GFS day 4-6 (small low pressure system, widespread snow)

  

12z GEM day 4-5 (troughing to North Sea low, widespread snow)

  

12z UKMO total precipitation to day 6 (precipitation generally similar across most areas, away from northern Scotland, and parts of the south coasts of Ireland and England).

A northwesterly brings the Cheshire gap into play, and showers and outbreaks of snow heading down there can bring snow to a large swathe of England, down into the Home Counties. In March, there’s more over-land convection too, pepping all this up further. I’m not saying that places further north don’t get more precipitation and lying snow than further south, but there’s plenty of scope for many western and southern areas to see a good bit of snow off a northerly setup. 

A northeasterly is a very different matter. As is those situations with a big west-east pressure difference, with a ridge building in. 

But with overtly cyclonic-derived northerlies, we get plenty of precipitation in the west and southwest, and when cold enough, plenty of snow that can lie for several days anywhere inland or with half reasonable altitude. And often in March too. 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815419

[Man With Beard]

Important to remember there are two narratives here: 1. longevity of the cold, and 2. frontal snow.

1. Longevity of cold: it seems likely the mild Atlantic air will not make it to the SW until at least D7, and then the mild boundary 'may' move northwards through England/Wales between D7-D10 but that's too far off for specifics.

2. Frontal snow. This is actually a big possibility, and perhaps more than once. Looking through the ECM ensembles individually, there is quite a large range of potential battleground snow scenarios on various days and regions between D6 and D9.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815479

[Met4Cast]

In terms of Thursdays channel low, here's the EC plot with each dot representing the possible positioning of the low within the EPS suite. A fairly significant spread as you'd expect at this range. 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815589

[nick sussex]

I’ve snipped out the important bits from the NCEP discussion.

By midweek and beyond the overall pattern becomes much more uncertain as it depends on the evolution of western Canada upper low energy as well as the details of the upper ridging over and south of Alaska. The resulting differences in upper flow pattern unfortunately lead to a wide array of possibilities regarding the sensible weather over the U.S. by the latter half of next week.

...Guidance/Predictability Assessment... Early in the forecast period Monday-Tuesday, model guidance remains in fairly good agreement with the overall pattern. This includes a western U.S. trough, a shortwave crossing the Midwest/Great Lakes region into the Northeast, and the latter's associated surface low. Thus early in the period, a multi-model blend of the deterministic 18Z GFS and 12Z ECMWF/CMC/UKMET was able to be used. But models and ensembles quickly diverged as issues with the amplified pattern atop Alaska/western Canada wreak havoc on the pattern downstream. There have been considerable differences from model to model and run to run within the same model suite. The 12/18Z GFS and the 12Z UKMET pull energy off into a closed low just offshore British Columbia by day 5/Wednesday and then the GFS has it sit over the Pacific, unlike the CMC and ECMWF. The 12Z ECMWF seemed to be fast with its trek of troughing moving eastward across the central U.S. by Thursday, and the new 00Z ECMWF did slow down with this. Overall the newer 00Z guidance seems to be in better agreement in principle fortunately. But for the WPC forecast with only the 12/18Z cycle available, had quickly transition to a blend heavy on the ensemble means from the GEFS, ECMWF, and CMC to create the forecast. Even the means were not terribly agreeable though in terms of the trough positions. There is some general agreement for ridging to come into the West by day 7/next Friday. Overall, predictability becomes quite low for the latter part of the forecast period and there may be more significant changes than usual in future forecasts during this time frame.

 

 

In the second paragraph you’ll see them mention last nights ECM op. We don’t want an early movement east of the trough they mention .

We need the jet to remain flat and not amplify upstream at the crucial timeframe as this will try and push energy ne and not east .

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815681

[Weather-history]

Stating the bleeding obvious

The further north you are, the increase chance of a longer cold spell.

The further south you are, the increasing chance of a shorter colder spell.

The shorter the cold spell in the south, the increasing chance of a snow event further north 

The longer the cold spell in the south, the increasing chance of a snow event further south  

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815716

[Met4Cast]

Broad signal now for a waining of our block towards next weekend as the Greenland high weakens and begins to retreat westwards into Canada. This is well sign posted across all models;

Before we get to that point there's a lot of details to be resolved re: snow showers, potential features within a very unstable airflow and that's before we get to any potential snow events as low pressure systems move in and bump into colder air. Plenty of snow potential for everyone before we arrive at next weekend. 

In the longer term a milder spell, at least further south seems likely into the following week as blocking wains and we see the Atlantic gaining the upper hand across the UK. MJO transitioning into phase 8 suggests broader teleconnective forcing will begin to fade with a fall in +MT followed by falling GLAAM, i.e, reducing westerly momentum within the broader wind-flow budget and as a result a less amplified jet stream. 

This serves to retract the Pacific jet slowly back westwards taking our blocking with it, i.e any blocking becoming increasingly west based and less favourable for UK cold. However, we're talking into the 2nd half of March for this rather than next week. 

Tropical forcing in the form of the MJO transiting through phase 8 combined with I suspect further downwelling of -ve SSW anomalies into the troposphere suggests another round of blocking potential around mid month/2nd half of March, albeit likely to be weaker than the first round due to the falling GLAAM & less favourable sub-tropical forcing as a result. Where this next round of blocking develops is uncertain but may initially occur to the north of the UK before becoming increasingly mid-lat based.

UK detail this far out isn't possible to ascertain but the broader picture through March is that below average temperatures are favoured overall.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815837

[nick sussex]

A small improvement in the ECM 06 hrs run to T90hrs .

The upstream trough is held slightly further n west and the Azores high is more suppressed .

Given the importance of very small margins this could make a difference down the line .

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815921

[Cambrian]

The first weather regimes probabilities extended forecast of the spring emerged yesterday evening. It shows the wall-to-wall Atlantic ridge regime of the first few days waning, and an increasing NAO+ signal, all in keeping with the pressure anomaly charts for weeks 1 and 2.

It’s very easy to appear to be labouring the point about uncertainty in the models, but I just wanted to point out that the Atlantic low makes very little eastward headway between week 1 and 2, the heights to the northwest remain throughout, as does the lower pressure running southward from the Barents Sea through Scandinavia. It has protracted battleground written all over it. Not going to get too hung up on the Atlantic low until we more clearly see the southwestward extent of the cold air by early next week.

  

The NAO+ signal peaks around the 16th of March, and subsequently diminishes in favour of increased blocking, so if the Atlantic isn’t in by then, it will be unlikely that it will get in at all during March. By day 15 on the 0z ECM ensemble mean, the core PV remains on the Siberian side, with low heights still extending down into Northern Europe. Colder uppers are moving back south over the UK and Ireland.

  

A neutral pressure anomaly for Scandinavia heading into the following week suggesting more of a block to the north between Iceland and Greenland, with lower pressure than usual to our south and southwest as the Atlantic low stalls and slowly sinks southeast.

From the ECM extended forecasts then, it’s still looking very much like a cold March, with the notable weather, perhaps very wintry, coming first from the north, a brief chance for the Atlantic, before the cold returns, and a potentially lengthy stalemate ensues. 

The models over the next few days are going to make compelling viewing!

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815972

[snowking]

We have been here so many times before, and for such a tiny landmass it's amazing what a difference just 50 miles north or south can make to the mood in here (geography dependent)

At this range, still 5 or so days away, we should still be scouring the ensembles and taking a consensus from the widest possible range of data available to us (within reason...we shouldn't be desperate enough to resort to the NAVGEM ensembles yet). MOGREPS is worth following here for such a reason, but all mainstream ensemble sets should be consulted. If we take the example of MOGREPS here:

When we see a spread from the Scottish Borders down to the north of France, we know that we're still a little while away from a resolution. It's probably also worth dropping in that, in my recent memory at least, MOGREPS-G does tend to be a bit of a follower rather than a leader, so if you start to see some continuity in MOGREPS which is consistent with other suites, you know you're probably honing in on a finalised track - and we're not there yet.

Through the course the of the weekend, especially once we get to Sunday, we should start to switch our attention further from ensemble suites and more towards the higher resolution runs, which should in theory at least have a better handle on things by this stage - this includes set and control runs as well as higher resolution suites which start to come into focus such as the UKV, but until at least Sunday, such outputs should not be taken entirely at face value.

All of this said, we've already seen one of numerous examples from over the years in this very winter of how even at T+0 models can struggle to get a grip on likely placement of such features - back in December, snowfall ended up some 50 miles further north than originally forecast. Historically, certainly prior to the middle of the last decade, I would have said that on balance these systems do tend to end up further south than modelled. However, whether the cause is improved modelling physic, a continuing change in our climate, or a combination of the two, since this point I have seen probably as many of these episodes end up further north as have ended up further south.

We probably will not be much the wiser until Tuesday in all reality, and even then we could theorise that the time of year renders some potential for disappointing marginality in events.

Until then, try and keep sane.

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4816138

[Paul]

For those who may not have seen it, @Nick F has written a really detailed blog looking at next week, the possibilities around it and the links with the stratospheric warming.

 

Cold northerly winds next week, bringing a risk of snow and ice, but how long will it last?

WWW.NETWEATHER.TV

---

Turning much colder next week with a risk of snow and ice, as winds turn northerly bringing cold air direct from the arctic. How long will the cold and wintry weather last...

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4816391

[The Enforcer]

T+90/96 Comparison:

ARPEGE 18z

GFS 18z

 ICON 18z

JMA 18z

UKMO 12z

ECMWF 12z

GEM 12z

NAVGEM 12z

CFS 12z

NASA/GEOS5 12z

 

 

 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4816683

[Cambrian]

The Band :

In early March, 2023, soon after the emergence of the SSW scene in the previous month, MJO persuaded the relocated tPV to record some work under its Phase 8 label. 

The original day 3 line-up, playing under the name ‘Arctic Blast’ featured drummer Siberian Lobe, lead vocals Greenland High, lead guitarist Scandi Trough and bassist Denmark Low, who together,  at the 0z ECM operational studios, cut two early albums of note - the impressive call-to-arms, ‘Cold Uppers’, and the more spiritually reflective ‘Jesus, It’s Got Parky All of a Sudden’. 

 

(click on images to see full details of tracks)

By day 5, they were joined by female grunge vocalist duo, The Atlantic Lows, to form a six-member outfit called ‘Battleground Synoptics’. There were clearly creative tensions from the outset, particularly with Greenland High, but during this period the band produced some stand-out tracks including the grindingly disruptive ‘Jet Stream Trough Collision’ and the searingly obvious ‘ Now We’re In For It’.

 

(click on images to see full details of tracks)

There then followed the golden ‘snowy’ era featuring perhaps much of their most memorable work, in three rapid-fire albums over the following three days - the exquisitely marginal ‘Snow In The South’ (featuring the mischievously titled single track ‘Spot the M4’), ‘Snow In The Middle’ and the very highly acclaimed ‘Snow Virtually Bleedin’ Anywhere’. 

  

The band struggled for a while after Greenland High’s departure, reflected in their later work, such as in the less popular ‘Mild Blip’, but soon came back in to form with the rallying cry ‘Didn’t Stay Long Though Didya?’  and the anthemically restless ‘Why Always a Day 10 Tease?’

   

(click on images to see full details of tracks)

Bristlingly relevant, simultaneously answering and questioning - and importantly, still going strong, a must-see band at the 12z’s festival, 5 stars 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4816845

[Met4Cast]

35 minutes ago, minus10 said:

Very interesting however a bit confused when you state that MJO transitioning into phase 8 will result in a weakening of teleconnective forcing and a less amplified  jet stream...i was under the impression that phase 7/8/1 was good for blocking and more jetstream amplification...especially if combined with SSW downwelling ?. Still  getting to grips with this stuff so maybe my understanding is not clear cut...thanks...

Phase 8 transition tends to lead to negative frictional torque, reducing mountain torque & then consequently reducing overall AAM, that’s what I meant by reduced teleconnective forcing.

The second half of my post then goes onto say the phase 8 MJO + SSW impacts may provide enough force for another round of blocking but likely weaker as the tropics (MJO) and subtropics (GWO) wont be working in sync quite as they are currently. 

The MJO isn’t a standalone driver, it’s better when used in conjunction with the broader GSDM. 

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815872

[bluearmy]

20 minutes ago, Met4Cast said:

I've got a feeling they were just simplifying things vs discussing the double warming. Technically it's the same SSW as not enough time had passed before the second warming/reversal.

The first warming displaced the vortex but that didn't propagate down to impact the troposphere, the second warming/reversal is the one impacting the surface. The NAM chart shows this quite well;

There usually is multiple "drips" into the troposphere though so another round of blocking seems plausible in the second half of the month after this initial block wains but with changing in sub-tropical forcing to something less favourable for high-latitude blocking we'd be reliant on the MJO & another downwelling from the SSW, which doesn't fill me with confidence personally. Plus it'll be getting on into March by that point so would take something even more special to produce.

The first reversal mid feb did not propagate quickly down into the strat - however, it’s normal to see a wave headed down at two to three weeks post warming. (And more to follow).  The second reversal looks to imprint into the trop within a week ….. is that just excellent timing and riding the downwelling wave from the first reversal?  None of us have the data to answer this. 

Extended ens already to picking up on another amplification by day 13/14, though just where that verifies is still being worked on.  If we do have two downwelling wave drivers through this month then we really are going to see a topsy turvy period of model watching which could sell take us through much of April too

Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4816882