South West/Central Southern England Regional Discussion 15/01/13 12z---->

[DavidLace]

Plymouth better not deploy its heat seeking snow destroying weapons.

[Sainsbo]

Ok. So when do I call off my weekend trip to London?! Meant to be driving up on Friday afternoon. Seriously! I don't know what to do! I'm meeting family for the first time.... Help!

I would atleast wait a little while. Things could dpossibly change between now and Friday (:

[AWD]

Found this on Ian's twitter feed;

@MattHugo new UKMO guidance agrees with you Matt, with change to rain in SW through Fri

Distinct possibility now.

Latest FAX also showing this, with the South West losing the continental feed on Friday as winds vear more southerly;

Edited January 15, 2013 by AWD

[jessandjon]

Plymouth better not deploy its heat seeking snow destroying weapons.

Pmsl!!! :-)

[Stoxs]

I would atleast wait a little while. Things could dpossibly change between now and Friday (:

yea it could Snow thursday as well!!!!

ramp ended

[cloudbase]

I'm hoping Friday's event pans out like the one I remember in the early 80's

I was in the car with my dad going to visit my Aunt and uncle in Weston (we were living in Worle) On the way in it started to sleet, we thought nothing of it and carried on. When we got there it was still sleeting, it was only about 30mins later that my mum phoned and suggested we should come home because it was snowing heavily.

Woke up the following morning to around 30cm's of snow.

There must have been a mild element to the weather at the time for it to start of sleeting, maybe it was a slider low like the one forecasted for Friday.

I bet the charts looked dicey if we were able to look at them back then like we do now.

Could this have been the winter of 1981, i remember moving from up north to Stogursey,Somerset in October and in early December the village was cut off for about a week.

[Jason74]

Interesting post from SK on the MOD thread:

For anyone still doubting snowfall potential from tonights ECMWF 12z, ive got access to the full suite

Dew points - sub 30F (damn americans, bear in mind 32F is 0c) for the whole run, bar some VERY limited periods of ~35F for the very far southern coastline, and some far south-western counties.

SK

EDIT - also add 850's to that. Sub 0c all the way through!

[Beast of Plympton]

Devon 1891

Devon 1963

Devon 1978

? ?

(please insert here)

Devon 2013

Those pictures are on Dartmoor I believe! I will insert the last one at the weekend... Hopefully its good!

[karlos1983]

As things stand, getting out of Wiltshire will be the tricky part. Get out of there and you should be fine as the snow shouldn't have reached further east at that stage.

However, a lot can still change in 72 hours so don't make any rash decisions at this early stage.

The only thing that screams is one maoooosive heating bill. I'd be bankrupt!

I'll pay it if it is snow cover

(Disclaimer, this is not a legally binding contract)

[BARRY]

It will be a miracle if it snows it only ever rains but if that wind stays SE well maybe Just maybe.

[chris55]

Just a quick post on all the parameters needed for snow fall.

The two main things we look for in these situations is the -5 line at 850hpa and the 528 line for thickness's, these are kind of bench mark values and in a very simple sense if these are favourable (below each of the stated figures) then snow will fall,

However!!!!

It's not as simple as that!!!

As Iceberg pointed out the 528 line is not as important with this set up. If you go back to post 252 there is a quick explanation.

Now onto the -5 850s isotherm. It is not always the case we need uppers to be this cold for snow to fall, with Fridays/Saturdays potential as long as we keep the 0C line south of us then snow could well fall anywhere within the colder layer (0c and below)

Take a look at this archive chart from 2009, this produce a lot of snow for the Westcountry,

-5 line well to the north of our region

From the Guardian;

"Further problems were expected for public transport, schools and businesses with severe weather warnings in place in south Wales, north Devon, Gloucestershire and Wiltshire today as snow continued to fall.

Forecasters said the worst of the weather was likely to be in the Midlands with as much as 10cm (4in) of snow, however the south and west of England and Wales ground to a halt today after waking up to their heaviest falls of snow this week.

The M4, particularly around Bristol and Swindon, the M5 and the M1 in the south Midlands were badly affected. Runways at Luton and East Midlands airports were closed, there were bus and train cancellations in Bristol and drivers were stranded in snow in the Cotswolds."

This just highlights that with a slight continental influence our usual -5 and 528 rules are less important.

Following from this if we look at the positioning of the 0c Isotherm on the GFS, ECM and UKMO we see it stays to the south,

So although the 528 line and 850s may look unfavourable, in these type of set ups snow can fall in air that may not at first glance seem to support it.

[Nights King]

Found this on Ian's twitter feed;

@MattHugo new UKMO guidance agrees with you Matt, with change to rain in SW through Fri

Distinct possibility now.

Latest FAX also showing this, with the South West losing the continental feed on Friday as winds vear more southerly;

it begins...

[Davey80]

Does anyone know how north Hampshire is placed with regards to snow. Basingstoke and Alton area? I'm confused.

[A.J]

it begins...

behave!

[Blizzardof82]

Just a quick post on all the parameters needed for snow fall.

The two main things we look for in these situations is the -5 line at 850hpa and the 528 line for thickness's, these are kind of bench mark values and in a very simple sense if these are favourable (below each of the stated figures) then snow will fall,

However!!!!

It's not as simple as that!!!

As Iceberg pointed out the 528 line is not as important with this set up. If you go back to post 252 there is a quick explanation.

Now onto the -5 850s isotherm. It is not always the case we need uppers to be this cold for snow to fall, with Fridays/Saturdays potential as long as we keep the 0C line south of us then snow could well fall anywhere within the colder layer (0c and below)

Take a look at this archive chart from 2009, this produce a lot of snow for the Westcountry,

-5 line well to the north of our region

From the Guardian;

"Further problems were expected for public transport, schools and businesses with severe weather warnings in place in south Wales, north Devon, Gloucestershire and Wiltshire today as snow continued to fall.

Forecasters said the worst of the weather was likely to be in the Midlands with as much as 10cm (4in) of snow, however the south and west of England and Wales ground to a halt today after waking up to their heaviest falls of snow this week.

The M4, particularly around Bristol and Swindon, the M5 and the M1 in the south Midlands were badly affected. Runways at Luton and East Midlands airports were closed, there were bus and train cancellations in Bristol and drivers were stranded in snow in the Cotswolds."

This just highlights that with a slight continental influence our usual -5 and 528 rules are less important.

Following from this if we look at the positioning of the 0c Isotherm on the GFS, ECM and UKMO we see it stays to the south,

So although the 528 line and 850s may look unfavourable, in these type of set ups snow can fall in air that may not at first glance seem to support it.

I remember that day well as the 6th of Feb 2009 was my wedding day

[liam300]

Does anyone know how north Hampshire is placed with regards to snow. Basingstoke and Alton area? I'm confused.

Read previous messages

[lynnsim]

Does anyone know how north Hampshire is placed with regards to snow. Basingstoke and Alton area? I'm confused.

I can't give you an expert's point of view (as I am not one!), but my met office phone app is showing light snow from friday afternoon through to saturday evening. So could be interesting in our part of the region too!!

[Iceberg]

Just to back that up Chris, gfs wet bulbs and 850 from midday Friday.

If we take a wet bulb of 200m which would give snow for those with a bit of elevation and sleet for anybody away from the coast we get the 200m line going along the Devon border along with -3 850s.

With this is mind -3 seems to be the zone of marginality with -4 or -5 prett much guaranteeing snow.

Of course heavier precip could easily drag the wetbulb down 50-100m.

I saw ian tweet but it goes against nearly all of the output I can find including metos own forecast. Unless he's really talking about turning to rain for Devon, coastal areas and maybe west Somerset.

I certainly can't see it turning to rain for glos wilts etc.

[Lynxus]

Four!!!

[Beast of Plympton]

For those in the far southwest who need a bit of a pick up, just looked at my local forecast on Met Office and the BBC for Friday and Saturday. It was issued at 7pm.

It is showing snow from 6 am friday morning until 9am saturday morning, then more saturday night.

However when I read the thread here it says devon and cornwall have been downgraded.

Can someone help me?? Bit confused!!

[gottolovethisweather]

Further to AWDs excellent analysis above, I'll also add mine.

Iceberg picked up on the Jetstream orientation and its implications. Have a look at the following to show why the GFS 12z was such a corker!

As before, I urge folks to view things from a global perspective, rather than worrying about surface features which haven't yet developed. This will only lead to confusion and subsequent overanalysis.

Some Five days ago, here was where the NH Jetstream was projected to be by Wednesday 16th January, 12pm

After this afternoon's run, here is the forecasted position for the day after, Thursday 17th January, 12pm

Totally different, chalk and cheese in fact look at where the NH Jetstream is. Several hundred miles WEST of the UK.

Then we go into the exciting and agonising period of t+96, Saturday 19th January, 12pm

I can only tell it how it is, but that shows a fantastic image of the NH Jetstream and as a piece in the puzzle of a perfect BATTLEGROUND scenario, just look at its positioning, bring it three days forward and its GAME ON.

Looking even further ahead is fairly pointless to be fair, but I will tease you with the NH Jetstream profile on Monday 21st January, 12pm (my birthday)

The NH Jetstream continues on its vacation southwards towards Africa.

Now let us look at the associated T850s from Thursday 17th January, 12pm, Saturday 19th January, 12pm and Monday 21st January, 12pm respectively.

Now onto finite details such SLP & Dewpoints which are very much subject to change as such a timescale. However, without the DP part of the puzzle, the rest of the jigsaw is not really worth analysing when it comes to SNOW.

Firstly remember the "HAVE SOME OF THAT" post from the other day showing the following.

What do you think the corresponding chart shows now at t+39.

I would say it is pretty difficult, not to say that that is an upgrade.

I will also attach the restricted to netweather Full Subscription members charts showing SLP & Dewpoints for the following timeframes. Wednesday 16th January, 12am, Thursday 17th January, 12pm, Saturday 19th January, 12pm and Monday 21st January, 12pm respectively.

All of the above charts cannot be taken literally as once SNOW is on the ground, should it in fact arrive and lay, the ground will cool rapidly and as a consequence modify the air above. Incidentally, all the charts away from the far Southwest suggest 12pm dewpoints very much condusive for snowfall.

As per the other day, I feel the deeper trend has to favour the atlantic bursting down the door but who knows when this will be. For now I suggest FANTASTY ISLAND lies between t+72 and t+96 at the latest.

Three tips I suggest when the BATTLEGROUND is in sight are to look for posts containing NAE output, NMM output and/or MetO Fax chart updates as before.

Edited January 15, 2013 by gottolovethisweather

[dec10snow]

Just to back that up Chris, gfs wet bulbs and 850 from midday Friday.

If we take a wet bulb of 200m which would give snow for those with a bit of elevation and sleet for anybody away from the coast we get the 200m line going along the Devon border along with -3 850s.

With this is mind -3 seems to be the zone of marginality with -4 or -5 prett much guaranteeing snow.

Of course heavier precip could easily drag the wetbulb down 50-100m.

I saw ian tweet but it goes against nearly all of the output I can find including metos own forecast. Unless he's really talking about turning to rain for Devon, coastal areas and maybe west Somerset.

I certainly can't see it turning to rain for glos wilts etc.

Yeah, thanks for the post, and you Chris so at the moment would you say I'm on the boundary?

[A.J]

Nice post Tony, with lovely use of coloured text...lol

Edited January 15, 2013 by ajpoolshark

[khodds]

Thanks everyone for your replies. Just emailed my sister.', to give her the heads up, if it all goes wrong now,it's my fault! Lol 😆

[AWD]

Just to back that up Chris, gfs wet bulbs and 850 from midday Friday.

If we take a wet bulb of 200m which would give snow for those with a bit of elevation and sleet for anybody away from the coast we get the 200m line going along the Devon border along with -3 850s.

With this is mind -3 seems to be the zone of marginality with -4 or -5 prett much guaranteeing snow.

Of course heavier precip could easily drag the wetbulb down 50-100m.

I saw ian tweet but it goes against nearly all of the output I can find including metos own forecast. Unless he's really talking about turning to rain for Devon, coastal areas and maybe west Somerset.

I certainly can't see it turning to rain for glos wilts etc.

Run the WBFL charts onto the next couple of frames and it edges that bit further north east.

So I agree that it Gloucs. & Wiltshire are still in a good position based solely on the GFS, but in can also see support regarding Ian's tweet with PPN turning to rain from the South West as far up as the M4 Corridor at least.

Detail like this will no doubt change over the next 72 hours anyway.