Model discussion highlights

[Paul]

Welcome to the Ronseal of model discussion threads - it's just model discussion, no frills, no snow watch and definitely no temper tantrums. 

If you want to talk about all the models in relation to all things snow during the coming days, the Snow Watch model thread is the place to go:

This thread is also acting as the model highlights thread, so when posts are marked as insightful by enough people in the snow watch thread, they'll be copied in here to, hopefully, add to the discussion. 

As ever, please keep it friendly and please keep it strictly on-topic.

[Cambrian]

Huge fun and games to come with the models through to Sunday with the battleground set up as it is. Snow-rain-snow events a distinct possibility for southern parts of the UK and Ireland and some parts no doubt seeing snow on snow. 

0z ECM ensemble mean for day 3 shows the cold holding on in the gap between systems through to the weekend,

  

before turning milder for all by next Monday, day 5, as the Atlantic low holds sway. 

  

Colder air returns by the following weekend, day 10, a chilly unsettled theme. 

  

The PV remains on the Siberian side of the Arctic, any brief signal for it to move over to the Canadian side being dropped yet again. With a cross-polar northerly flow arriving to us as a northwesterly, colder spells remain a good possibility well into the second half of March. 

Edited March 8, 2023 by Cambrian

[Eagle Eye]

I'm not a short-term forecaster so here's my long-term look as to the general direction of everything and the 00Z as an example.

A typical NPJ setup given an equatorward shift of the jet is for a retrogressing Alaksa-Kamchatka block and some sort of +VE heights into the W US. That drops the cold into the E US. Right now it appears that setup is likely in some form. That changes the pattern of the jet by slightly firing up the jet just off the eastern seaboard and the RWT is weakened and lands more towards the mid-Atlantic. This is a setup similar to the PM air around mid-Jan for the UK with the SE US ridge and mid-Atlantic ridge. That helps with the trend towards a PM airflow for the next effects of the RWT. Initially, the pull is just from the WNW and that really struggles to pull in cold but as the high moves further North it pulls it more from the NNW and so mid March may bring in chilly air again. Its likely going to be a difficult start to Spring given the fairly strong MJO response to the SSW and the +VE AAM coupling together. So with 1 or 2 RWT's and Iberian based European heights may struggle to fully build in until the E US pattern flattens out and fires up the jet.

Composite

Realtime and forecast as the NPJ trends equatorward as it retracts slightly.

Given this occurs from a +VE NPO state what affects may that have elsewhere? It may help with rising out of La Nina slowly but surely with a w'ly wind burst in the ENSO-calculation area. Recent examples of the +VE EP/NPO helping with transition to El Nino in Winter would be 2014-15 change, 2018-19 change and 2001-02 change. There was a failed one 2002-03 however that occurred from an El Nino state in the first place. 1992-93 was a failed attempt from a neutral state as well. Mostly, the examples of a La Nina and +VE EP/NPO pattern did support this idea and we're seeing that in the forecasts. We could climb out of La Nina into neutral-El Nino territory.

 

[Blessed Weather]

Looking at a couple of key indicators going forward it seems likely that the next couple of weeks or so will provide the last opportunities of 'proper' winter type weather for this season.

The sPV looking to gradually recover from the SSW to near seasonal normal by month's end:

Zonal winds

Temp Anomalies

Sources:
https://www.stratobserve.com/anom_ts_diags
http://www.weatheriscool.com/prod/interactiveTserie.html

And the MJO moving through Phase 8/1 will likely continue to play a role in attempts to establish some high latitude blocking for a couple more weeks before disappearing into the COD zone of no influence by month's end:

GEFS extended:  ECM extended:

Source: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

[Cambrian]

Heehee  ….hectic, there must be something really good on TV. 

The 6z GFS operational run for day 8 shows the Atlantic trying to make inroads into cold air in place over the UK and Ireland. Ring any bells?! Though more from the west on this occasion than the southwest to be fair.

  

Reasonable support from the ensemble mean too. Another low about to merge at the base of the Siberian - Scandinavian trough, being pointed southeast as it does so and looking keen for disruption, with impressively cold mean uppers lying in wait. 

  

Brings us back to the frequent discussion of many months of how slow-moving the hemispheric patterns have been, and how broad longwave patterns that affect weather in specific parts of continents (in this case, the influence of the Siberian-Scandinavia trough on Northern Europe), can last for several weeks once they get established. 

This episode, around the middle of the month, could be an interesting few days, before the flow turns more westerly from around day 12 and Azores heights begin to nose up towards the UK and Ireland, while the PV overall is beginning to show signs of its seasonal contraction, the colder uppers slowly withdrawing northward. 

  

By then, the equinox, many might be more ready for something more resembling spring, but whether such an easily reinforced cold pattern gets turned around that quickly might be another thing. 

[Rain All Night]

The ensemble means aren't showing any signs of anything interesting or pleasant coming up...

The only bit of interest I can find is a small EPS cluster in days 11-15 that shows a bit of high pressure to our north, but not enough to do anything interesting...

I can see why this thread isn't getting as many posts as the other one!!

Edited March 8, 2023 by RainAllNight

[mountain shadow]

ICON cold all the way out to next Thursday with the Atlantic never really making it in and the jet well to the South..Spring on hold

[seabreeze86]

GEM really keeps us in a cold pattern with another northerly and heights rising to the north west 

[Eagle Eye]

6 hours ago, Eagle Eye said:

  

 

 

Ignore this, this appears to be an old chart of something because it starts the forecast in 2022 yet was issued February 2023 though I might just be reading it wrong. Anyway, we are moving towards Neutral-El Nino territory with the cold pool anomalies filtering out already.

 

[Allseasons-Si]

Where is the GEM control going

[Cold Winter Night]

Usually everyone looks at the big hemisperic picture at long lead times and zooms in to regional charts at short lead times for events like we’re in right now, but for your personal experience and insight it’s good to take a mental note of today’s weather for your location (snow/rain/dry) with this synoptic setup at T+0h for the Northern Hemisphere:

Might come in handy to draw from that when, say, two winters from now something similar to these synoptics pops up in some GFS run at 384h.

Which takes me to verification. When today was still Day 10, EC did a very fine job at 240h amid all the post-SSW chaos:

GFS and GEM were both far off:

Edited March 8, 2023 by Cold Winter Night
Missing word

[Rain All Night]

No UKMO 12z +168h/HD maps yet... was hoping it might show something to liven up this thread...

The GFS and GEM ensembles are both showing hints of raised heights to the north after the TPV has moved away towards the far east.

[Bricriu]

2 hours ago, Cold Winter Night said:

Usually everyone looks at the big hemisperic picture at long lead times and zooms in to regional charts at short lead times for events like we’re in right now, but for your personal experience and insight it’s good to take a mental note of today’s weather for your location (snow/rain/dry) with this synoptic setup at T+0h for the Northern Hemisphere:

Might come in handy to draw from that when, say, two winters from now something similar to these synoptics pops up in some GFS run at 384h.

Which takes me to verification. When today was still Day 10, EC did a very fine job at 240h amid all the post-SSW chaos:

GFS and GEM were both far off:

Well, that's maybe bad news for next week then. I was hoping the GEM solution would be correct. 

[Rain All Night]

22 minutes ago, Bricriu said:

Well, that's maybe bad news for next week then. I was hoping the GEM solution would be correct. 

The 850hPa temp ensembles for Reading are all showing a mobile pattern with an 'amplitude' of something like 10°C or more in terms of upper temps for the next week or so, which I think is something we've not seen for quite some time as it's generally been continuously mild during all the wet spells I can remember for at least the last 10 months down here!

At least this will be something different for anyone who was bored by February. I wasn't... can I have my mid-latitude high back please..?!

Edited March 8, 2023 by RainAllNight

[damianslaw]

One aspect of the models compared to recent weeks - knocking on 2 months now, is a much wetter spell of weather kicking in. Where were these conditions in second half of Jan and February... we are having a major switcharound moment courtesy of the effects of the SSW.. I'm always nervous when dry benign weather goes on for weeks - wait for that switch to turn on and the heavens open! All suggestive atmosphere is an abnormal slow moving state, with patterns entrenched for long periods dry or wet..

[Eagle Eye]

MJO forcing signal from Phase 7/8 has worked out quite well as a general forecasting tool given the strong reaction of the MJO to the SSW. We have to take into account the initial setup which was favourable for driving of N Atlantic AWB and the Greenland-Scandi dipole. Then we are seeing the retrogression of the RWT energy scattering signal driving the Alaska-Kamchatka dipole and the N Pac signal keeps strongly +VE and that forces the w'ly wind burst into the Nino area and La Nina is being pushed up towards neutral territory.

Phase 8

Forecasting beyond now as we move towards MJO Phase 1 reaction time. That looks to be quite strong so composites may be a fair way to look at this considering the initial state which is likely to be a retrogressing Alaska-Kamchatka high with weak +VE heights Canada-Greenland. Combine that with the exiting E US low and initially returning SE US ridge of sorts that may tamper with the downstream reaction. Without the Alaska high and it being retreating signal and the N Canada blocking is likely to retreat as well; this appears to be linked with C US - E US LP system. Dwindling mid-Atlantic-Greenland +VE heights and the return of the NE Canada LP system is likely to fire up the jet as we go into early Spring but after an initial PM-esque airflow. The jet is likely to extend in the Atlantic with the E seaboard -VE heights exiting and that helps with MJO Phase 1-2 typical reaction but eventually as we go into the April part of Spring we are likely to see the return of the SE US ridge with C US trough's. Though it is likely to help with the low pressure system belt in the Atlantic making it likely that Spring starts with finding it fairly difficult to be warm. 

Phase 1 mid- March

Phase 2 early April

Ignore spelling mistakes or anything like that, I wrote this late at night.

 

[Blessed Weather]

A look at the NOAA/CPC 8-14 Day 500mb outlook and the GFS Jet Stream forecast shows a mobile westerly pattern with frequent low pressure systems moving in from the Atlantic to bring wet and windy weather to the UK. GFS suggesting 6 systems over the next 2 weeks. The UK looks to stay either in the direct path of the Jet or just to the north of it, so cool to cold temperatures - particularly on the back edge of systems as they move through and pull in colder air - with further snow at times for Northern England and Scotland but rain/sleet for the south. Deep cold never too far away to the north, but atm insufficient amplification in the pattern to pull this south.

NOAA 500mb outlook 16th-22nd March:

Jet Stream snapshots 14th Mar  21st Mar

Next Mon/Tue 13/14th standing out as a spell of very windy weather as a vigorous low pressure system crosses Scotland. So even after the current cold, snowy spell, still lots of interesting weather showing in the models.

GFS  ICON 

ECM

[johnholmes]

For net wx 0900 Thur 9 th March 2023

Looking at the 3 charts I have on my daily check on the NOAA output, there has been a slow increase in the contour heights from north to south. The latest shows the 540DM line just about on the Scottish border.(see below). The air with that still originates from fairly high latitudes over the Pacific and ne Russia so not especially mild. A 546DM contour is shown over southern England.

 

With these charts being very consistent in their evolution I am pretty confident they will be shown to be about ‘right’ 6 days from now. So the deep cold has certainly been moved well north with even much of Scotland in the slightly less cold air. Turning to the 8-14, covering the period 16-22 March and the pattern remains much as the 6-10, the 540 DM is now over northern Scotland with the 546DM still over southern England.

This all suggests that snow is going to become confined to the highest hills of northern England with only the far north of Scotland likely to be seeing any snow falling below about 5-800 ft. That is when there is any ppn! Turning to the ECMWF 10 day charts by the 13th onwards and the 850 MB charts show the -5 C line moving to the north of Scotland before returning to the south of Scotland by the 19th. As is often the case EC and NOAA are not on the same page so to speak but not on different chapters. Overall, along with the synoptic outputs from the 3 main models I would suggest that PM air with surface flow from a westerly point is the weather pattern 6-14 days from today. Neither very mild nor very cold weather patterns are likely for any period.

Of course I may be talking nonsense but then weather forecasters can only do their best with outputs at their disposal; egg on face is a professional hazard so bear with UK Met as they grapple with the next 72-96 hours let alone beyond.

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Original post: https://community.netweather.tv/topic/98485-model-output-discussion-snow-watch-limited-edition/?do=findComment&comment=4825594

[IDO]

Looking at the next ten days, there is no sign of northern blocking returning, more a westerly flush and classic cold zonal with the north invariably getting colder than the south. Wedges are sent north but are fluid, so there is no sustained block, like the GFS showed on previous runs (GFS moved towards ECM on 0z). The ECM:

After D10 on the GFS, we get a cool, wet trough over the UK for 5+ days, but that looks like an outlier versus the ensembles, which continue with a more zonal flow:

     

^ Pressure charts showing op with little support for UK trough.

Original post: https://community.netweather.tv/topic/98485-model-output-discussion-snow-watch-limited-edition/?do=findComment&comment=4825319

[Rain All Night]

Have been trying to get the "heights build to the north as the TPV moves away further into Siberia" idea to stick to the 5-day averaged ensemble means. Have kinda sorta got it on 2 out of 3 of them this morning:

Though it doesn't show on the ECM mean, you can nonetheless see it in the clusters:

It looks like the flow would be tilted with lows heading southeast into Europe in this scenario, around the equinox.

Edited March 9, 2023 by RainAllNight

[Cambrian]

Extremely interesting 24 hours coming up for many as the system pivots in the early hours bringing the band of snow back southeast, as shown here on the 6z GFS and 9z ICON-EU. North Wales and the North Midlands are the northern extent of the milder air for a few hours only, the rain-snow boundary quickly back down to sea level and during the night time hours too. 

  

Don’t be surprised if the cold air undercuts earlier in the night than this on the western flank and that there could be more precipitation than currently shown with it pepping up as it is over Northern Ireland this afternoon.  

There could be quite a sting in the tail of this one. 

Original post: https://community.netweather.tv/topic/98485-model-output-discussion-snow-watch-limited-edition/?do=findComment&comment=4826170

[Eagle Eye]

La Nina has now ended so we can't blame our future weather on it as we go into neutral. Don't really have much more to add. Should start climbing over the next few weeks potentially towards El Nino.

Edited March 9, 2023 by Eagle Eye

[Rain All Night]

Has the TPV started shrinking for the Spring now? Or am I imagining it?

[Skullzrulerz]

1 hour ago, Eagle Eye said:

La Nina has now ended so we can't blame our future weather on it as we go into neutral. Don't really have much more to add. Should start climbing over the next few weeks potentially towards El Nino.

What would a EI Nino mean for our weather and what would it reflect on the models?

[Eagle Eye]

8 minutes ago, Skullzrulerz said:

What would a EI Nino mean for our weather and what would it reflect on the models?

I'm not sure about Summer as the ENSO reactions are less amplified in Summer but it's generally better for Winter cold because El Nino Winters tend to be less zonal than La Nina Winters. Too late this Winter with just neutral but generally next Winter might have slightly better cold chances than this one when thinking about the whole season.

Edited March 9, 2023 by Eagle Eye