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

[OldMetMan]

Is this on the METO website mate or was it created by yourself? Cheers.

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.

As I mentioned earlier, there is the added risk of freezing rain if we get a shallow, slightly warmer feed off the Channel along the coast. I hope I'm wrong!

Edited January 20, 2013 by OldMetMan

[Wilxy]

Sorry to cause confusion, this is from myself. It's likely the MO will be issuing a yellow warning initially with an amber once clarity sets in. The amber some-where along the lines of the 60% or perhaps 40% most likely.

Would just like to say i really like your forecasts and to be fair you have been quite good at getting things right i remember a few years back with thunderstorms that it looked unlikely then you turned up issued a forecast and bingo it happened, although this could still change but hopefully not as it would be amazing to see more snow on top of whats still on the ground.

[Thermohaline Conveyor]

My analysis techniques are rather similar to those of the MO, use a lot of experience and a blend of the different models adopting super ensembles where possible. Confidence is growing on this coming event, it'll be interesting what Ian Fergusson's latest thoughts on this are. Could be quite a bit of disruption. UKMO, ECM, GFS, BOM and NAE all on board in terms of the low progression and to a certain extent the alignment of the -4/-5oC T850 frontal boundary. Could get very interesting!

Edited January 20, 2013 by Thermohaline Conveyor

[chris55]

And he has an uncanny knack of being right!

Yes I do remember TC doing very well over on TWO a few years ago.

It was the big snow event with the red warnings, Jan 2010. The flow looked like a dry northerly, Met didn't warn of anything, but TC and Gavin P both highlighted the risk of a Low spinning up in the flow, and that happened with lots of snow for some in the south.

It went from cold dry unassuming northerly,

To Snowmageddon, in 48 hours!

[Thermohaline Conveyor]

where did you get that from mate or did you just made it up urself lol ???

All mine. I have been forecasting and analysing the weather for many a year.

[AWD]

The latest UKMO run shows the area of PPN growing in size between 42 and 60 hours. Some heavy rates of PPN to for some.

Upper air temps remain cold throughout, as do surface temps away from the far SW, with winds turning increasingly easterly.

Good UKMO output for our region,

[Thermohaline Conveyor]

Yes I do remember TC doing very well over on TWO a few years ago.

It was the big snow event with the red warnings, Jan 2010. The flow looked like a dry northerly, Met didn't warn of anything, but TC and Gavin P both highlighted the risk of a Low spinning up in the flow, and that happened with lots of snow for some in the south.

It went from cold dry unassuming northerly,

To Snowmageddon, in 48 hours!

Hi Chris,

I remember that! Fascinating looking back on past snow events. I'm not too far away from you now, I'm based in Tibberton North Gloucestershire.

[latitude]

My analysis techniques are rather similar to those of the MO, use a lot of experience and a blend of the different models adopting super ensembles where possible. Confidence is growing on this coming event, it'll be interesting what Ian Fergusson's latest thoughts on this are. Could be quite a bit of disruption. UKMO, ECM, GFS, BOM and NAE all on board in terms of the low progression and to a certain extent the alignment of the -4/-5oC T850 frontal boundary. Could get very interesting!

GFS shows the -5 850 leave the SW Monday night.

[WhiteFox]

Snowing all day in Maidenhead. But if anything it has thawed more than its settled!

Same here in Reading. Rather odd to have light to occasionally moderate snow for much of the day yet finish with less than you started!

I can only assume that the surface temp was above freezing for most of the period.

[Iceberg]

The latest UKMO run shows the area of PPN growing in size between 42 and 60 hours. Some heavy rates of PPN to for some.

Upper air temps remain cold throughout, as do surface temps away from the far SW, with winds turning increasingly easterly.

Good UKMO output for our region,

Hit the nail on the head there awd, the track of the low will determine how far north the precip gets and how much of the milder weather (dps upto 2 or 3 with wet bulb at 600 m for some are possible as a worst case scenario.

Gfs less keen on instability in the wrap around, but its likely to be a resolution issue.

[festivalking]

Phew! The hills are alive with snow, sledges and irresponsible drivers. Incredible people decide to park anywhere causing the most horrendous queues. Not sure how these people get licences, it was embarrassing to watch.

Back to the weather looking like cold rain for devon and cornwall according to latest bbc weather for monday and tuesday.

[chris55]

As AWD said,

UKMO ppn, decent

850s -5 for most,

Hi Chris,

I remember that! Fascinating looking back on past snow events. I'm not too far away from you now, I'm based in Tibberton North Gloucestershire.

Hey TC Westcountry rules! lol.

[fergieweather]

My analysis techniques are rather similar to those of the MO, use a lot of experience and a blend of the different models adopting super ensembles where possible. Confidence is growing on this coming event, it'll be interesting what Ian Fergusson's latest thoughts on this are. Could be quite a bit of disruption. UKMO, ECM, GFS, BOM and NAE all on board in terms of the low progression and to a certain extent the alignment of the -4/-5oC T850 frontal boundary. Could get very interesting!

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.

[Iceberg]

Meto really hits the nail on the head. Hopefully country file weather focast will incorporate this set of models and we can see what the meto are thinking for Tuesday.

[Wilxy]

fingers crossed that theres no change in 24 hours.

[stuboy]

Thats exactly what happend in most parts on the SW on Friday.

It just hasent been cold enough at 2m.

Same here in Reading. Rather odd to have light to occasionally moderate snow for much of the day yet finish with less than you started!

I can only assume that the surface temp was above freezing for most of the period.

Still have a bit to come according to the radar (we're right on the edge here!), and the temp on my flat balcony is now below 1 degree for the first time today and falling. It does seem to be settling a bit more as we head towards the evening and colder conditions.

[Frosty_wsm]

Thats exactly what happend in most parts on the SW on Friday.

It just hasent been cold enough at 2m.

Luckily that wasn't a problem here on Friday, still got plenty of snow on the ground now, even went for a drive though town and the sea front earlier and plenty of snow there still too, hopefully it can see a top up sometime this week before the possible milder weather comes in next weekend.

Edited January 20, 2013 by Smartie

[dec10snow]

Same here in Reading. Rather odd to have light to occasionally moderate snow for much of the day yet finish with less than you started!

I can only assume that the surface temp was above freezing for most of the period.

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

[dec10snow]

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 don't want to miss the main part of it again!

[latitude]

Luckily that wasn't a problem here on Friday, still got plenty of snow on the ground now, even went for a drive though town and the sea front earlier and plenty of snow there still too, hopefully it can see a top up sometime this week before the possible milder weather comes in next weekend.

Strange that, seeing Weston is on the coast? Suppose you havent seen a thaw yet?

[fergieweather]

Meto really hits the nail on the head. Hopefully country file weather focast will incorporate this set of models and we can see what the meto are thinking for Tuesday.

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.

[dec10snow]

Some pretty heavy PPN now pushing in to the south east coast!

[Wilxy]

Temp -0.6c now and dew p -2 and temp slowly falling again now so any thaw should now stop or slow down.

[chris55]

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.

Yes I have noticed NAE chopping and changing with each run, not surprising, given the set up. Interesting to hear ECM was bringing in snow tomorrow. Who knows what will happen.

Edited January 20, 2013 by chris55

[fergieweather]

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...!!