South West England Cold Spell Discussion

[Wilxy]

What is going to happen crutial now 3.1°c and not budging oh dear game over here unless it can fall rapidly during the front's presence.

[aspire27]

Beautiful day here - leaden skies, raw wind and light drizzle and 2.5C.

Sleet now mate.

[MP-R]

Sleet now mate.

Yep, nice one! Just looked out the window and definitely sleeting at this end too.

[BristolBlizzard]

Yep, nice one! Just looked out the window and definitely sleeting at this end too.

Good signs, although its not sleeting here yet

[Ian Fergusson]

A little note to stress that the snow risk for upland Glos (especially) is reflected by the UKMO FLASH warning (valid to 1800hrs) for good reason. The transient snowfall reliably reported thus far to the BBC from various people in the Forest of Dean, some parts of Cotswolds and indeed further afield (e.g., near Radstock, B&NES) is a precursor to this second frontal zone / PPN swathe now moving northwards.

This 2nd one (well modelled late yesterday by the NAE) will prove somewhat more vigorous, with marked vorticity advection up aloft, imbedded instability and advancing against (and over) the increasing easterly undercut.

It's in recognition of this feature and its potential that the FLASH remains active for Glos. Notably, the NAE and high-res models remain keen - even after the earlier more widespread rain - to call for around 10-15cm snow potential in lowland Wales, West Midlands, Forest of Dean, Cotswolds and some other areas north of the M4.

Given the already knife-edge scenario for PPN discrimination effectively Bristol northwards (e.g., sleet / soft hail reported fairly recently in some S. Glos districts), it would not take much in terms of heavier PPN to drop the WBFL suffiently to introduce snow at lower levels.

HOWEVER, as repeatedly expressed yesterday, for many (most) this will continue as a rain event.

Attached the latest NAE output for the WBFL progression this afternoon and idea of wintry/rain PPN discrimination - note how this becomes more widespread into the afternoon, for reasons mentioned above.

It's about as good as we can offer short of nowcasting and our Chief Forecaster (and fab scientist) presently at UKMO Ops Centre - Bob Wilderspin - really does know his stuff when it comes to modelling / forecasting snowfall... indeed his (co-authored) methodology is now widely used there to modify raw PPN signal in NAE output. So let's see how things develop.... it's a fascinating set-up.

[MP-R]

Good signs, although its not sleeting here yet

Only in heavier bursts though as we know, alternating between moderate sleet and drizzle. More than I expected though lol, temperature around 2.4C.

[musician]

Completely off topic and as a Mod, I should know better but, I've got to ask - Musician, did you go to Chippy school?

Hi! Yes! I certainly did! Mum still lives there. I wonder how you made the connection?

Better add a weather item for the moderator - temperature has risen to 2.8 and we have drizzle.

[SilverWolf]

Thanks Ian, really appreciate the professional input. Feeling like interesting times here in Stroud! It can snow at the top of town and not the bottom here, unfortunately i'm at the bottom!

[aspire27]

more and more sleet now.

[ronant]

A little note to stress that the snow risk for upland Glos (especially) is reflected by the UKMO FLASH warning (valid to 1800hrs) for good reason. The transient snowfall reliably reported thus far to the BBC from various people in the Forest of Dean, some parts of Cotswolds and indeed further afield (e.g., near Radstock, B&NES) is a precursor to this second frontal zone / PPN swathe now moving northwards.

Interesting stuff Ian - thankyou. Living in North East Wiltshire we saw a little sleet 10 mins ago as the precipitation got heavier but now its back to slightly lighter rain.

Could i ask the situation for Thursday? Your post yesterday did say there was the chance of some very heavy snowfalls, but ive seen no mention of that anywhere since. What's the latest?

[Jonesywilliteversnow]

temps begining to drop here now at 3.1 from 3.3 30 mins ago! its light drizzle here atm

[Wilxy]

No sleet here either just light rain seems slightly milder here then than in yatton.

[MP-R]

No sleet here either just light rain seems slightly milder here then than in yatton.

Bristol does tend to be a tad milder than North Somerset and that could make all the difference in these sort of situations. The rain has to get a bit heavier though for the sleet to be a feature.

[BristolBlizzard]

thanks ian .

[dogs32]

Excellent post Ian thx for your thought's,

well not sure if I should go up the hill or not.

If I leave it to late I wont be able to get some good pic's.

Then again snow look's good at night.

Current drizzle here with temp at 3.3

Edited December 29, 2009 by dogs32

[Dartmoor_Matt]

Ian, thank you as ever.

Any chance though we could get some imput to the weather in the extreme SW or are we consigned to the mild wet weather therefore get no mention?

Beginning to wonder if the weather is so different in one part of the SW to the other than perhaps we need more definition in the threads.

[BristolBlizzard]

sleet in south britol now .

[musician]

A little note to stress that the snow risk for upland Glos (especially) is reflected by the UKMO FLASH warning (valid to 1800hrs) for good reason. The transient snowfall reliably reported thus far to the BBC from various people in the Forest of Dean, some parts of Cotswolds and indeed further afield (e.g., near Radstock, B&NES) is a precursor to this second frontal zone / PPN swathe now moving northwards.

This 2nd one (well modelled late yesterday by the NAE) will prove somewhat more vigorous, with marked vorticity advection up aloft, imbedded instability and advancing against (and over) the increasing easterly undercut.

It's in recognition of this feature and its potential that the FLASH remains active for Glos. Notably, the NAE and high-res models remain keen - even after the earlier more widespread rain - to call for around 10-15cm snow potential in lowland Wales, West Midlands, Forest of Dean, Cotswolds and some other areas north of the M4.

Given the already knife-edge scenario for PPN discrimination effectively Bristol northwards (e.g., sleet / soft hail reported fairly recently in some S. Glos districts), it would not take much in terms of heavier PPN to drop the WBFL suffiently to introduce snow at lower levels.

HOWEVER, as repeatedly expressed yesterday, for many (most) this will continue as a rain event.

Attached the latest NAE output for the WBFL progression this afternoon and idea of wintry/rain PPN discrimination - note how this becomes more widespread into the afternoon, for reasons mentioned above.

It's about as good as we can offer short of nowcasting and our Chief Forecaster (and fab scientist) presently at UKMO Ops Centre - Bob Wilderspin - really does know his stuff when it comes to modelling / forecasting snowfall... indeed his (co-authored) methodology is now widely used there to modify raw PPN signal in NAE output. So let's see how things develop.... it's a fascinating set-up.

Ian, we really are so lucky to have your imput on this forum! Many thanks for such an articulate, measured and informative account!

[Bristawl Si]

Just thought i'd 'pop in' during my lunch break at work. Rain and cold here in Nth BTL. Interesting post from Ian. Not much change from yday really.

Looks like we'll miss out here. What is it about that bl##dy M4? was it built all those years ago to screw our chances of snow?

And how is the new years eve/day event looking? From what i've read on the model discussion thread seems to be a downgrade from what was being said a couple of days ago. Then it seemed we were heading for a monster cold spell with snow. Now....not a lot from what i can make out!

[Ian Fergusson]

Interesting stuff Ian - thankyou. Living in North East Wiltshire we saw a little sleet 10 mins ago as the precipitation got heavier but now its back to slightly lighter rain.

Could i ask the situation for Thursday? Your post yesterday did say there was the chance of some very heavy snowfalls, but ive seen no mention of that anywhere since. What's the latest?

Thursday remains subject to considerable uncertainty - primarily, how quickly the frontal zone decays as it sinks southwards, having (we expect) lost the principal upper forcing off westwards. The likely result - on present balance - is a spell of fairly widespread but generally light and increasingly fragmented snowfall into southern-central England, with the focus ever towards the SE, but crucially some EPS members (a not insignificant minority) want to spin things up somewhat down in the SE and increase the heavy snow risk. But present consensus is for ligher snow, a very cold evening (New Year's Eve) and widespread ice risk.

Edited December 29, 2009 by Ian Fergusson

[TimMB]

Sleet here in Clevedon

[Defector]

Thank you Ian, appreciate you taking the time to write on the forum.

All the best,

Phil.

[Ian Fergusson]

Just thought i'd 'pop in' during my lunch break at work. Rain and cold here in Nth BTL.

Sleet in Bradley Stoke 10 mins ago - quite prolonged bout of it - so assume same up the road in Stoke Gifford! Heavier PPN now less than 10NM to the SSW heading north.

[Nights King]

Still have rain/sleet/rain/sleet here on mendips. It just doesnt look like the heavier ppn will reach my neck of the woods so snow probably less likely. temperature is 2.9c

had wet snow first thing which got washed away fast though.

Edited December 29, 2009 by mullender83

[Ian Fergusson]

Ian, thank you as ever.

Any chance though we could get some imput to the weather in the extreme SW or are we consigned to the mild wet weather therefore get no mention?

Beginning to wonder if the weather is so different in one part of the SW to the other than perhaps we need more definition in the threads.

Hiya - yes, sadly (assuming you like snow) it's a wholly wet, windy and grim affair anywhere essentially from Exmoor / Mendips southwards today and doubtless tomorrow too. You'll not from the frames I just posted off the NAE how virtually all of the SW region -as defined by the UKMO - sits beneath the milder regime but as stressed yesterday, don't dismiss the the rainfall totals or possibly localised flooding impacts, either!