Model output discussion - here comes the beast!

[tight isobar]

17 minutes ago, Man With Beard said:

One of the peculiarities of the models coming up may be snow where you don't normally expect it. Southern extremities such as IOW, S Devon and the tips of S Cornwall could see major disruptive snowfalls if the winds go direct E or ESE for a prolonged period, as a "channel streamer" may set up as shown in the fax charts. This is a big, big possibility. 

Yeah-id buy that devon-cornwall dorset-running along to coastal counties...and IOW..

may see best deposits in a very long period!!!

That not taking away preety much anywhere else running through nxt week!!

4

Edit; but highlighting marginality-as non problematic....

Situ given.

Edited February 23, 2018 by tight isobar

[ItIsGee]

4 minutes ago, MR EXTREMES said:

I want it further south to keep cold holding on.

2009/2010 was classic for channel runners but the convection from the northeasterly was amazing.

Just a cm or 2 would make me smile.

i suppost in the long run yeah keep the cold at bay but id like to see 2 or 3 FEET!!!!

[John Cox]

The Irish Met service (Met.ie) has put out its 1st snow/ice warning:

National Weather Warnings

 

STATUS YELLOW

Weather Advisory for Ireland

Exceptionally cold weather is forecast for next week with significant wind chill and severe frosts. Disruptive snow showers are expected from Tuesday onwards, particularly in the east and southeast.

Issued:

Friday 23 February 2018 12:00

Valid:

Friday 23 February 2018 12:07 to Friday 02 March 2018 12:00

Edited February 23, 2018 by John Cox

[Tog]

21 minutes ago, swebby said:

Only just glanced at the fax charts, not sure i've ever seen one with a convergence line set up over the channel, pembrokshire dangler yes but over the channel, no.  Would make for some interesting weather in the channel isles....

We always have ‘interesting’  weather, gales and fog.  Though rarely snow, 2013 was mega though,  got skis out for that occasion! 

[Summer Sun]

High res NMM showing the cold air (850's) spreading west across Europe looking like the -14s will be hanging around for a wee while

[KTtom]

10 minutes ago, MR EXTREMES said:

I want it further south to keep cold holding on.

2009/2010 was classic for channel runners but the convection from the northeasterly was amazing.

Just a cm or 2 would make me smile.

There are a lot of people in the west and wales who want it a good deal further north as the 00z gfs....only chance of snow in these parts  even if there is a thaw following.

[Dean E]

9 minutes ago, swebby said:

Quick Q - This is the result of generalised upper wind flows so may have a tendency to move in location? I.e it's not a fixed topographical feature as we see with the Pembrokeshire dangler that results from the Irish and Welsh mountains/hills during a northerly?

MWB - yes i was thinking IOW could well see some significant falls from the current set up but the channel isles is a surprise. Scilly Isles might also find this problematic, especially as they'd be well into the flower producing season which i believe is a large part of the economy.

I recall the Channel Islands doing very well from a similar setup in March 2013, where a low moved up from France, producing 50cm+ over the islands. The front never made it to the South Coast, but we did get some convective showers instead.

I still can't believe we are seeing such good outputs this close to the time frame, really is a 2010 and 2013 in the making this setup. Models have done a good job at this SSW induced cold spell thus far.

[Paul]

4 hours ago, Paul said:

Here's what the (9km) Netwx-Mr model is thinking in terms of snow cover at the end of the week.

Usual caveats - it's one run blah blah, so subject to significant change. Plus specifically, we know that this version of the model is still not high enough resolution to pick up all the convective stuff, or resolve snow amounts with as much accuracy as the 3km version of the model, but that only goes to 2 days, so we'll have to wait and see what that starts to show!

 

Just wanted to follow up, as the 6z run is much snowier!

Still the same caveats though....

[Man With Beard]

16 minutes ago, swebby said:

Quick Q - This is the result of generalised upper wind flows so may have a tendency to move in location? I.e it's not a fixed topographical feature as we see with the Pembrokeshire dangler that results from the Irish and Welsh mountains/hills during a northerly?

MWB - yes i was thinking IOW could well see some significant falls from the current set up but the channel isles is a surprise. Scilly Isles might also find this problematic, especially as they'd be well into the flower producing season which i believe is a large part of the economy.

I think this GFS chart gives a nice example of where we might get to even without frontal activity (aside a band through N England/Ireland)

Those southern extremities shown up, and just a small change in windflow could elevate these figures massively - Channel Islands doing very well, and Isles of Scilly likely to go white. Bristol Channel streamer likely to affect N Devon (Cardiff seems a bit ambitious?). N coast of Wales also gets a good snowfall. Any any east coasts, and up to 100 miles inland would see moderate amounts I expect.

I'm actually quite comfortable calling this as far ahead as D6 because there isn't a great pattern change on the horizon between D3 and D6, and that's when higher uncertainty would kick in. Not this time though - the block looks quite well set for a few days. For me, Thursday or Friday are the days where something different might materialise, but once the cold is in there's only one way to get it out and that will involve snow. I think!!

(EDIT: I think Nick F's post above demonstrates this well - I'm guessing the huge difference in snowfall occurs on Thursday/Friday next week?)

 

Edited February 23, 2018 by Man With Beard

[Luke Best]

2 hours ago, Interitus said:

This article from the Meteorological Society Weather journal is worth reading at this point - An historical and climatological note on snowfalls associated with cold pools in southern Britain - http://onlinelibrary.wiley.com/doi/10.1002/wea.666/pdf

Jan 1987 rates as the record deep cold pool at around 495/496 dam 1000-500mb thickness.

The authors say -

In fact that whole edition of the journal from Jan 2011 is freely available and is a special issue focused on severe winter weather and worth a look for those inclined -

http://onlinelibrary.wiley.com/doi/10.1002/wea.v66.1/issuetoc

Here's an interesting excerpt:

"We have not seen such an absence of deep cold pool events since the 1970s, and therefore, in spite of global warming, who is to say that, following 1956 and 1987, the next extremely deep cold pool event will not visit us in January or February 2018?"

Considering that was written in Jan 2011, that's not a bad call!

[Duane S.]

Let's get this into perspective...

I've doctored the 06z ens below, which is for my tropical area of the UK.

Looks very decent still doesn't it!? And then... then you realise how bonkers the original, un modified, chart actually is.

 

[KTtom]

2 minutes ago, Paul said:

Just wanted to follow up, as the 6z run is much snowier!

Still the same caveats though....

....and the same gaps over western parts Can someone find a model with no gaps please! 

[swebby]

3 minutes ago, Luke Best said:

Here's an interesting excerpt:

"We have not seen such an absence of deep cold pool events since the 1970s, and therefore, in spite of global warming, who is to say that, following 1956 and 1987, the next extremely deep cold pool event will not visit us in January or February 2018?"

Considering that was written in Jan 2011, that's not a bad call!

Excellent, so a thirty one year repeating pattern.  So for the next one that'd make me - hmmm best not to think about that......

Edited February 23, 2018 by swebby

[JeffC]

1 minute ago, KTtom said:

....and the same gaps over western parts Can someone find a model with no gaps please! 

Yeah, odd one that as 2010/11 easterly we got plenty of snow...but then again these are modelled, they aren't hindcasting so guess patience is a virtue...

[Yarmy]

2 minutes ago, KTtom said:

....and the same gaps over western parts Can someone find a model with no gaps please! 

You want a NOGAPS weather model?

 

https://en.wikipedia.org/wiki/Navy_Operational_Global_Atmospheric_Prediction_System

[tight isobar]

3 minutes ago, Man With Beard said:

I think this GFS chart gives a nice example of where we might get to even without frontal activity (aside a band through N England/Ireland)

Those southern extremities shown up, and just a small change in windflow could elevate these figures massively - Channel Islands doing very well, and Isles of Scilly likely to go white. Bristol Channel streamer likely to affect N Devon (Cardiff seems a bit ambitious?). N coast of Wales also gets a good snowfall. Any any east coasts, and up to 100 miles inland would see moderate amounts I expect.

I'm actually quite comfortable calling this as far ahead as D6 because there isn't a great pattern change on the horizon between D3 and D6, and that's when higher uncertainty would kick in. Not this time though - the block looks quite well set for a few days. For me, Thursday or Friday are the days where something different might materialise, but once the cold is in there's only one way to get it out and that will involve snow. I think!!

 

All good via your interp's...

Although north-sea convection and wider-spread inland shower activity...still being very much underplayed here.

As have backing of possible deeper feature influence @continent.

Some eye bulging (potential) via possible accumulates from above mentioned mon- weds....

Then after perhaps a more organised event.....OR THREE!!!

[JeffC]

2 minutes ago, Yarmy said:

You want a NOGAPS weather model?

 

https://en.wikipedia.org/wiki/Navy_Operational_Global_Atmospheric_Prediction_System

might as well use my model  - NOHOPES!

[Rayth]

11 minutes ago, Paul said:

Just wanted to follow up, as the 6z run is much snowier!

Must admit I’m slightly concerned given I’m in the red zone ( Newcastle upon Tyne ) yikes 

[tight isobar]

1 minute ago, Raythan said:

Must admit I’m slightly concerned given I’m in the red zone ( Newcastle upon Tyne ) yikes 

'Again'..

All very speculative atm..

But firmly expect-quite notable upgrades via ppn charts by sunday.

And certainly more extensive!!!

Prime conditions @convective influence.

[Robbie Garrett]

1 hour ago, karlos1983 said:

ECM ens still corkers!!!! All the way out!

we’ve hit the jackpot guys n gals! Be sure to enjoy it!!! Especially you lucky bunch down the eastern side of the UK! I don’t envy you, I’m happy for you! Going to be memorable for many!

 

 

Look at some of those runs, -15*C in London almost on one in FI. :O

[swebby]

22 minutes ago, s4lancia said:

Let's get this into perspective...

I've doctored the 06z ens below, which is for my tropical area of the UK.

Looks very decent still doesn't it!? And then... then you realise how bonkers the original, un modified, chart actually is.

 

Yep, ensembles tend to be the first thing i check.  Glanced at the 850's/ppt 0z's for devon (although not much different from most of southern/central England) and thought the control would deliver snow, with the Op a milder/marginal solution for the 2nd/3rd of March. The 6z has dropped the Op now to where the control was on the 0z in terms of 850 temps but has again kept the control lower than the op.  Is this indicative of a trend or just an shows that the track of the low south of the uk is still guesswork. I'd say the latter.

Edited February 23, 2018 by swebby

[Frosty.]

As a coldie..this all feels like a wonderful dream that you never want to end!!

The Ecm 00z ensemble mean is a dream run with persistent very cold conditions and snow!❄❄❄❄❄❄❄❄❄❄

[East_England_Stormchaser91]

I still cannot believe what I'm seeing for now just a few days out. No doubt about it, this is going to have many people gobsmacked, especially those who pay no attention to forecasts etc. A lot of the new younger generation are going to find out what a proper dumping of snow looks like that's for sure. 

[BleakMidwinter]

14 hours ago, CameronWS said:

Would that head north into Scotland?

Cameron, you should go and look in the Scotland regional thread - I started in there when I lived up in Scotland and imo the Kilted Thread has the most accurate regional people going.

You'll get a really good answer in there, specific for your region of Scotland too. 

Tell 'em I sent you and they might even buy you a pint
 

 

[Snowy Hibbo]

 

A quick update on the torques situation. MT is deeply negative, pushed by a low EAMT, creating the Pacific jet retraction that we are currently in. FT is steadily rising, generated from a WWB in the Pacific and a Kelvin wave in the IO, however it is still in the negatives. I did a whole tweet thread on that, if you are interested.

The current GWO situation brings the AAM near to zero, showing the transition from the +AAM orbit, that helped bring about the SSW, to the -AAM orbit that brings about the Pacific jet retraction. Shows how involved the AAM is.... 

 

GEFS currently shows MJO going into the COD on the 1st March in Phase 2.

This would help bring about a more +FT outlook, with the MJO signal weakening in the IO. This moves to +MT, etc....

The Pacific jet retraction isn't normally very helpful for the UK snow-wise. It normally forms with the -AAM state, to create a +NAO/ zonal setup. But in this case, the NAO is going to be deeply negative, thanks to the SSW. So the Pacific jet retraction is just a consequence of the drop in the AAM. As known, the GWO's orbit into the positive AAM stages help create the SSW, as part of the dual entity that the MJO and GWO are, but with their own individual identities.

Anyway my other opinion would be on my tweet thread up above. I am wishing you all bucketloads of snowfall and very cold temperatures across the UK (unless you don't like snowfall, then I guess stay next to the fireplace?)