Model Output Discussion - A cold start to Spring?

[BLAST FROM THE PAST]

On 04/03/2023 at 16:48, Tim Bland said:

Looking forward to seeing the charts to back this up? 

Patience Tim…FI charts aren’t worth me posting as they don’t back up anything as they are FI.  I believe they’ll be coming.  Mused this first thrust was too early? this is far from done deal….as we see the shift back towards the cold hanging on and re-surging.  Be very interesting to see what they show come Friday. In the meantime stacks going on in the models this week ahead.

BFTP

Edited March 6, 2023 by BLAST FROM THE PAST

[kold weather]

7 minutes ago, Man With Beard said:

Some of the modelled snow looks outrageously marginal. Take ARPEGE for Wednesday night in the south. Snow with 0C uppers!

Yeah, timing is going to be really important for this. If we can get it between 02-07z that should setup a hold enough base. If it comes outside that time i fear a struggle to get much settling.

It does also highlight one added benefit of March in these setups, a colder sea which tips the balance in these tight setups.

[weirpig]

Seeing as lately  there seems a Alaro love fest.  That models is showing (for the bits we can see) a 7 or 8 hour spell of snow for many eastern parts  on Tuesday    very similar to its 0z run . 

Edited March 6, 2023 by weirpig

[Blessed Weather]

Please stick to model output discussion in here. Posts about Met Office warnings should go in the Met Office/BBC Outlook thread and posts asking will it snow imby should be made in the appropriate Regional thread or Spring Chat thread.

I'm afraid further off-topic posts will likely be removed. Thank you.

[EML Network]

7 minutes ago, IDO said:

A good GFS in FI this run:

A couple of trigger lows dropping and pulling in cold air.

Building blocks for an Easterly setting up there too !

[Stuie]

Ah here is the 3am 0C Isotherm. Courtesy of NW.

 

EDIT: And here is real time data of where the LP to the East is positioned.

Edited March 6, 2023 by Stuie

[Anthony Burden]

Morning all,as I mentioned in my blog several days ago next week could deliver snow and cold after a short blip GFS shows this nicely,in the meantime cold with snow in many places with a short breakdown Friday then a rinse and repeat which incidentally the Canadian model showed some days ago but it’s operational was classed as an outlier due to ensembles.

[minus10]

Seems that gfs 6z is throwing stormier weather in the mix for later..

...that would be quite something in the north sea if it verified..unlikely of course but shows whats possible..anyway this week is enough to be getting on with i think...

[DAVE_ALLEN]

2 minutes ago, minus10 said:

Seems that gfs 6z is throwing stormier weather in the mix for later..

...that would be quite something in the north sea if it verified..unlikely of course but shows whats possible..anyway this week is enough to be getting on with i think...

The Azores low lends a hand to the Atlantic block development

[Mike Poole]

When there’s lots of uncertainty like this, I like some of the probabilistic output, here’s the % risk of snow throughout the week from the PEARP (ARPEGE ensemble):

Most of us in with a shout there at some point!

[Cambrian]

Two aspects of today’s output are striking. 

Firstly, the formation of that cut-off low across the UK and Ireland and its subsequent movement into the North Sea around day 4/5 puts a local cat amongst the global pigeons.

Here are the last four GFS operational runs (12z, 18z, 0z, 6z) for the early hours of Saturday. The low appeared with a bang in the 18z run, was less of a feature in the 0z, but is shown deeper again and closer to the east coast on the latest run. The westerly in the south / easterly in the north has been replaced by a northerly flow through all parts. 

   

Secondly, to the west, the edge of the lower heights running along the bottom of the Atlantic low to Ireland and the UK is just getting flatter and flatter for around day 5, the shallow undulations being stretched straight, reinforcing the idea of the models picking up on more scope for disruption of the advancing lows. The 12z yesterday had the ejection of a 990mb trough across Ireland and the UK. Today’s 6z keeps the 995mb isobar about 200 miles west of southwest Ireland. As well as its trough being held off further west, the Atlantic low itself is being edged south to the east of Newfoundland. 

To the south, the 584 gpm height contour over Iberia is slowly being adjusted south since its zenith on the 18z run, and to the north, the 512 gpm line from the PV has steadily been pushed further south too, now running through northeast Scotland, so the overall heights gradient is similar but the pattern is being shunted south. The core PV heights in the Norwegian Sea continue to lower, and moreover, the Norwegian Sea trough is well and truly holding its ground in the reliable. 

 

As a result, by day 8, early next week, we’re back to square one, returning into the Arctic air, 512 gpm low heights digging south into the middle of the North Sea, possibly even colder in the south of the UK than this week, and a channel runner thrown in for good measure. The Atlantic trough has by then given up the ghost. 

This all still has a great deal of firming up to do, and we still don’t know where the most intense battles will line up over the next few days, but we are beginning to get a much clearer idea of which side will ultimately win. 

Edited March 6, 2023 by Cambrian

[Snowy L]

Interesting that the Met say the highest risk of snow tonight is in the South of the warning area but the lowest wet bulb temperatures are clearly towards the NorthEast of the warning area. Definitely not bringing this up out of Imby desperation by the way

 

 

 

Edited March 6, 2023 by Snowy L

[dryfie]

Recent thicknesses (1000-500hpa & 1000-hpa) plus 850hpa temperatures

Thicknesses.xlsxThicknesses.xlsxThicknesses.xlsx

 

 

Edited March 6, 2023 by dryfie

[DAVE_ALLEN]

So the met office have called it. They appear to have gone against the latest fax charts for disruptive snow keeping it along southern counties and south of the M4.  
 

I expect the 12z ECM and this evenings fax charts to update on a par with this.  The current runs seem to slowly coming together albeit there is still diverse solutions even at this short range. 
 

this would suggest more of a channel low set up moving E and then ESE up the channel rather than a frontal system moving NE up the country 

Edited March 6, 2023 by DAVE_ALLEN

[Chertseystreamer79]

3 minutes ago, Snowy L said:

Interesting that the Met say the highest risk of snow tonight is in the South of the warning area but the lowest wet bulb temperatures are clearly towards the NorthEast of the warning area. Definitely not bringing this up out of Imby desperation by the way

 

 

 

Do they mean as it slips away south the back edge is more likely snow (ne region),  there for as that slips away more southen areas of the warning at more risk??

[tight isobar]

The points - predict- are now firming! Itsa London / Home Counties watch through  nxt 18/40 hrs!! The meteocial point de- ros/ and wet bulbs will be vital!!.. the prognosis of ebb. N flow/ via   Cutting lps and digging of polar air.     Will be SUBSTANTIALLY driven!!- I’ll put my punts out later

Edited March 6, 2023 by tight isobar

[alexisj9]

1 hour ago, Man With Beard said:

Some of the modelled snow looks outrageously marginal. Take ARPEGE for Wednesday night in the south. Snow with 0C uppers!

Won't argue that it isn't marginal, however here in Kent we get help from continental DPs in easterly winds. It should be fine unless uppers go positive.

[Downburst]

1 hour ago, snowking said:

Just to put this into context, this means that the entirety of the ECMWF Ens suite will be higher in horizontal resolution than any operational run from any other medium range suite. And we now get access to the lot. There's more to it than just horizontal resolution but in effect we'll have an additional 50 deterministic runs to mull over. Weather nerds assemble.

And daily 46 day output if I read this correctly. Added to all this is the ongoing improvement in satellite input like Meteosat-12 as example. Great news.

[tight isobar]

The DAM line will indulge much further south than stale data suggests!! Some news making snowfall- looks inevitable!!

[throwoff]

Anyone else just desperate for the 12z now..

[Ali1977]

Just now, MattStoke said:

Sucks to be in the Midlands this week.

Or one moves north and one moves south and they get double whammy!! I imagine the Thurs system will start as snow further south below the warning, but quickly turn to rain - looking at the charts anyway 

[Catacol]

I'm not going to be popular....but I think a lot of folk are going to see cold rain for the most part this week - and nothing close to approaching 2018. At elevation a different story but unfortunately for me the setup has gone awry. Blocking to our north is set to transition westwards very quickly and this will allow the atlantic to come in much flatter than we want. There is no block for these systems to bump and slide against, instead a cold trough pushing in from the NE but the cold trough itself isnt making sufficient inroads to get entrenched cold in place as we did at least manage to get in early December.

Why? The origins of a less wintry setup I think lie in the worry I had last week, namely that the remnants of the vortex setup too far east. This was a change to what was modelled initially and it has worked against getting artic air to flood far enough west. You can see it clearly here - setup last night shows the block in place and the deep trough over Scandy

and then wind forward 72h and the trough has essentially gone nowhere - stalled due to lack of momentum inspired from aloft because of the positioning of the SPV

Heights pulling very fast towards Canada, atlantic pushing in a merging with the Scandy trough - and for me this is classic nasty cold rain conditions for the vast majority away from Scotland.

To labour the point a bit - here is the vertical profile of the vortex right now

way - way out east whereas back in the days when the SSW was getting exciting this was where it was projected to be:

Location and angle have changed and absolutely not to our advantage.

Note also how the MJO has panned out: we hit phase 7 in good time.....and it died. It dropped into the COD taking away the signal for northern blocking when we wanted it and is now surging dramatically once again into the West Pacific - but much too late to give support to our current pattern this week.

This suggests a chance for renewed blocking in the second half of the month, but I think in truth by then it is too late for any deep, sustained cold. Spring will be on its way.

Not the right time for an end of season reflection yet - things can and do change and I hope this post is left looking daft in 3 days' time as people wade through the drifts...but for me another opportunity looks set to slip by. I have seen more frost this year than in many years but for swathes of the south I think this winter is going to go down as a "so near and yet so far" kind of season. 

[Purga]

1 hour ago, Man With Beard said:

Some of the modelled snow looks outrageously marginal. Take ARPEGE for Wednesday night in the south. Snow with 0C uppers!

Yes but the DP's are very low!

[Scott Ingham]

22 minutes ago, Snowy L said:

Interesting that the Met say the highest risk of snow tonight is in the South of the warning area but the lowest wet bulb temperatures are clearly towards the NorthEast of the warning area. Definitely not bringing this up out of Imby desperation by the way

 

 

 

This isnt the Met lmfao its met4cast who posts on our website hahaha

[minus10]

Interesting the different model interpretations of the low on Friday..

Ecm 0z

Ukmo 0z

gem 0z

gfs6z

icon 6z

mo fax

mo video

..cleary the mo making more of this low thus bringing in milder air further north..of course still 4 days away...a long time in meteorology currently..