South West/Central Southern England Regional Discussion 20/01/13 10z------------->

[Blizzardof82]

Well we haven't altered tune set by the GM over last 2 days of enhanced snow threat for parts of W Country (mostly to north and M4 corridor) growing overnight Mon into Tues but given differing handling & genesis of smaller scale low centres in GM, NAE & EC through Monday into Tues we'll not go heavy on possibility as yet. Continuity is v v poor on ppn issues. E.g. EC generates 2-4+ cm snow Bristol etc 12-18z tomorrow. NAE didn't but just about to see chief's new views from 12z.

Thanks Ian for your continued input on this forum it really is excellent to have your valued point of view on current situation.

[BARRY]

Well it has not got above freezing here all day so i'am going to put this down as one of our rare ice days

[Jayfromcardiff]

So, chief goes for rain into Cornwall tonight. Tomorrow maybe 1-3cm snow in some southern areas during day. Perhaps Somerset southward etc. Tues occlusion will see a yellow warning issued. Much uncertainty & v marginal on snow issues from approx Bristol S'ward with 400m WBFL effectively Bristol down into Somerset. Snow signal from Bristol northwards. No detail trustworthy or worth over-analysis at this juncture. Certainly nothing akin to Friday's story last week in terms of confidence levels...!!

Hi Ian, would SE Wales be included in the yellow warning as the NAE has indicated the potential of heavy snow? Cheers.

[Iceberg]

Cheers for that Ian I use to have a link to a web page where you put in the taf and got the chief forecasters summary for that area maybe 5-10 years ago now shame we don't have those back door entries any more but good your on here to give it to us

[Nights King]

So, chief goes for rain into Cornwall tonight. Tomorrow maybe 1-3cm snow in some southern areas during day. Perhaps Somerset southward etc. Tues occlusion will see a yellow warning issued. Much uncertainty & v marginal on snow issues from approx Bristol S'ward with 400m WBFL effectively Bristol down into Somerset. Snow signal from Bristol northwards. No detail trustworthy or worth over-analysis at this juncture. Certainly nothing akin to Friday's story last week in terms of confidence levels...!!

So are we talking snow to high ground somerset only?

[Costa Del Fal]

So, chief goes for rain into Cornwall tonight. Tomorrow maybe 1-3cm snow in some southern areas during day. Perhaps Somerset southward etc. Tues occlusion will see a yellow warning issued. Much uncertainty & v marginal on snow issues from approx Bristol S'ward with 400m WBFL effectively Bristol down into Somerset. Snow signal from Bristol northwards. No detail trustworthy or worth over-analysis at this juncture. Certainly nothing akin to Friday's story last week in terms of confidence levels...!!

Ahh, thats a shame to hear for us Cornwall lot tonight. Perhaps not completely out of the question for any wintriness down here but Meto symbols all day have trended more and more to rain tonight.

[SnowChance24]

Hi Ian, would SE Wales be included in the yellow warning as the NAE has indicated the potential of heavy snow? Cheers.

It will be interesting to see where the yellow warning covers. I was within the 'Amber' area for Friday and no snow settled and had mostly freezing cold rain all day! It must be a nightmare to forecast due to the localised nature of settling snow in some areas.

[Fred Sykes]

Fergie give us some snow, fergie fergie give us some snow. Fergie give us some snow, fergie fergie give us some snow!! One things for sure Ian, this cold spell is certainly going into Fergie time if it continues up until next week end!

[WhiteFox]

I had that for Friday's event during the day!

I think a few things helped here on Friday:

1. The lighter snow started early in the day so temperature didn't have time to rise

2. Cloud was thicker so no warming from sun

3. 850s marginally lower

4. Intensity of ppn meant more settling.

All factors that were not in our favour today!

[Thermohaline Conveyor]

So, chief goes for rain into Cornwall tonight. Tomorrow maybe 1-3cm snow in some southern areas during day. Perhaps Somerset southward etc. Tues occlusion will see a yellow warning issued. Much uncertainty & v marginal on snow issues from approx Bristol S'ward with 400m WBFL effectively Bristol down into Somerset. Snow signal from Bristol northwards. No detail trustworthy or worth over-analysis at this juncture. Certainly nothing akin to Friday's story last week in terms of confidence levels...!!

Thank you for this Ian, close to my thoughts. It is all very diffuse, and models are chopping and changing rather erratically. Do you have access to ECM PPN models? It's quite limited on the ECM front, online. I usually try to calculate the absolute vorticity by positioning of a low pressure system and the ECM ENS Mean projected positioning of the -4oC frontal boundary, attempting to calculate PPN intensity is rather more challenging using this methodology.

[Dampdorset82]

There is increasing confidence that an area of low pressure will bring its attendant weather fronts in across the South West during the course of Tuesday bringing another period of potentially significant snowfall to parts of South West and Southern England.

We have issued a % probability of disruption due to snowfall on Tuesday with the most emphasis placed on areas immediately around and South of the M4 corridor with some areas to the North of the M4 also included. Main counties of concern for the risk of 5-10cm or perhaps more are currently North Somerset, North Dorset, Bristol, Gloucestershire, Wilts and Hampshire.

There remains some uncertainty on snow totals and the extent of the snowfall to the South and close to coastal areas, it's likely that precipitation will fall as rain and sleet initially across Devon, South Somerset, South Dorset and Coastal Hampshire, but as the cold air undercuts later it's likely to turn increasingly to snow - giving accumulations.

The main snow line is generally in line with the M4 corridor with strongest and most persistent signals for severe disruption around the Forest of Dean, Bristol, Bath and Central/Southern Wilts into North Somerset and North Dorset.

The Northern extent of the band could also be extended and progression East across the South Coast to affect West and East Sussex also remains a possibility.

We'll have further updates through the course of today and tomorrow.

I think its important to remember that Fridays Snow wasnt forecast to fall as snow on the south coast untill pretty close to the event........I for one will not be looking at that type of information with too many inconsistancies between models and positionings of LPs and PPn.

Just to show this, the attached picture shows Christchurch (mudeford) beach

Edited January 20, 2013 by Dampdorset82

[Nights King]

Well another ice day today with temperature maxing out at -1c and now down to -2.1c so if it clears tonight it could drop very low indeed.

Going to be alot of radar watching next 2 days and nowcasting as this forecast for next few days changes each run

[Costa Del Fal]

Actually looks like tonights precipitation for Cornwall will now not make it much past Truro-Bodmin-Newquay areas so may be too light for any wintriness im afraid. Still, as Ian et al. are suggesting, lots of uncertainty this week with a variety of different fronts and features on the go which may cause surprises here and there!

[latitude]

Looking for a decent low temp tonight. Hopefully -0.9 will be beaten!

Not that cold since our cold spell started 8 days ago.

Temperatures IMBY have been 1 to 2 degrees warmer than all BBC forecasts. Anyone else had that?

[Uncle Gargy]

The sky looks full of it already. Been getting snow pellets most of the day.

[latitude]

Actually looks like tonights precipitation for Cornwall will now not make it much past Truro-Bodmin-Newquay areas so may be too light for any wintriness im afraid. Still, as Ian et al. are suggesting, lots of uncertainty this week with a variety of different fronts and features on the go which may cause surprises here and there!

Cold rain it seems falling on cold surfaces so ice could be the only problem.

[chris55]

Thank you for this Ian, close to my thoughts. It is all very diffuse, and models are chopping and changing rather erratically. Do you have access to ECM PPN models? It's quite limited on the ECM front, online. I usually try to calculate the absolute vorticity by positioning of a low pressure system and the ECM ENS Mean projected positioning of the -4oC frontal boundary, attempting to calculate PPN intensity is rather more challenging using this methodology.

He is the Local forecaster on the telly! But you knew that.

I'd think Ian has access to every model ever made lol.

[124alex]

So next weekend, is going to be milder without any snow?

[Argyle1980]

I still have a good feeling about it snowing tonight in Truro :-)

[theprophecyman]

So next weekend, is going to be milder without any snow?

Think that's "possible" view from reading one of Ian's earlier posts..... (below)

It's a highly diffuse forecast re any semblance of local let alone regional detail through next 48-72hrs. Our broad note of caution is that given such low static stability, anything could happen, frankly. Our only area of high confidence is for a breakdown next weekend but clearly any detail on this isn't worth paper written on at current juncture.

Edited January 20, 2013 by theprophecyman

[Blizzardof82]

So next weekend, is going to be milder without any snow?

Too far out, who knows we may get another undercut and strengthing of our block. I always look at these situations through rose tinted spectacles and dont really have a clue but nothing wrong with hopecasting

[Nights King]

Think that's "possible" view from reading one of Ian's earlier posts..... (below)

It's a highly diffuse forecast re any semblance of local let alone regional detail through next 48-72hrs. Our broad note of caution is that given such low static stability, anything could happen, frankly. Our only area of high confidence is for a breakdown next weekend but clearly any detail on this isn't worth paper written on at current juncture.

Yes I wouldnt worry about this just yet as last friday/saturday was also forecast to be a breakdown and we all know what happened.... Still out in FI so probably but not certain.

Maybe our SSW will put breaks on mild?

[divadee]

So far we have had an ice day. Highest temp so far has been -0.4c

[fergieweather]

Thank you for this Ian, close to my thoughts. It is all very diffuse, and models are chopping and changing rather erratically. Do you have access to ECM PPN models? It's quite limited on the ECM front, online. I usually try to calculate the absolute vorticity by positioning of a low pressure system and the ECM ENS Mean projected positioning of the -4oC frontal boundary, attempting to calculate PPN intensity is rather more challenging using this methodology.

Sadly the contractual restrictions on ECMWF means I'm not allowed to post their ppn or snow probability output whilst it remains part of current forecast.... sorry, not my decision!

[fUnKy]

-0.1 now in plymouth... First ever negative reading.

maybe no snow but that's cheered me up.