Severe Weather - Monday 17th Oct

[Nick F]

Convective / Storm forecast - Issued 17/10/2011 06:00

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Valid: 17/10/2011 06:00 - 18/10/2011 06:00

Headline: ... THERE IS A SLIGHT RISK OF SEVERE WEATHER FORECAST...

Synopsis

Strong upper trough to the NW extending down from the arctic crosses northern Britain today, at lower levels - a deep low exists just SE of Iceland at 06z with a sharp baroclinic zone lying from the mid-N Atlantic east across N Ireland/S Scotland ... by 12z frontal boundary is expected to lie from Galway (Ireland) - Dundee with a frontal wave along it across Nern Eire ... by 18z frontal wave expected near NE Scotland while cold front surges SE across Wales and N/central England.

... S SCOTLAND, IRELAND/N IRELAND, N ENGLAND, WALES, MIDLANDS ...

An active cold front developing along a strengthening baroclinic zone across Ireland/N Ireland and S Scotland this morning is expected to surge SE across England and Wales this afternoon and evening - with heavy rainfall associated with its passage. A narrow tongue of tropical maritime air advecting NE ahead of the front will likely be subject to forced ascent along frontal zone as colder air undercuts behind. Line convection could develop as a result of this forcing, given strong upward motion indicated by GFS vertical motion charts. Given rather strong tropospheric winds under jet stream and marked veering of surface winds indicated near/along this front, strong low-level shear will exist which will support potential for severe weather if sufficient instability can evolve. Should shallow line convection develop - dry mid-troposheric air; low LCLs and strong speed and directional shear will support potential for damaging convective wind gusts (60-70mph) along with one or two isolated tornadoes. So have given a SLIGHT risk for these areas - mainly for this afternoon. Lightning maybe isolated or absent with this line convection

... MON NIGHT - N and W SCOTLAND, N IRELAND, NW ENGLAND and N WALES ...

Cold Pm airmass following cold front, with 500mb temps around -30C spreading south, will be characterised rather steep lapse rated across Nern Britain tonight and over the next few days. As a result, vigorous convection is likely towards northern and western coasts of the above areas as the cold air crosses the warmer SSTs, with hail and thunder likely in cells that move ashore on the nortwesterly flow.

Issued by: Nick F - Forecaster for Netweather

[Coast]

Just checked the rain and this looks significant for a while across a Northern band of the country:

[Liam J]

Wind is increasing all the time here with a few showers passing by, expecting the main action from about 3pm until around 5pm during the passage of the cold front with the strongest winds just ahead of the front and as it passes the wind will shear quite markedly and change direction from S-SW to NW so I expect very lively gusts in the process.

[kold weather]

Models seem rather keen on developing a squall line, so today should be very interesting to watch...

Also if the intensity is right then high ground over Scotland and N.England will have a shot at sleet/snow, esp in the heaviest of stuff. I have to admit when i saw the ECM run a few days showing snowfall over a large area of high ground in Scotland i was fairly spectical, but it does look like the evap cooling effect maybe enough for high ground to get something.

Going to be interesting day, had this been in Jan I think things might have been ever more interesting!

[Cheshire Freeze]

Could be quite a vicious one this; also I would say that all of the models tend to underestimate scenarios such as these in terms of the convective element. I've seen pokey little squall lines sweep southwards in the past which have shown up as little more than light rain on precipitation forecasts.

[Coast]

Snowfall for 12 hrs ending Mon 17 Oct at 12am GMT

http://www.snow-fore...atic/uk/24/snow

[Liam J]

NAE 6z has a very tight pressure gradient over NW England this afternoon, wind really ramping up here now.

the NAE model has shown this feature very intense and maintained over the last few runs.

Edited October 17, 2011 by Liam J

[kold weather]

Yeah the NAE has been quite keen on really tightening up the pressure gradient in the NW, much more then most of the other models from the looks of things.

As for snow, as has been said, high ground over Scotland and IMO possibly over the higher ground of the Lake District will have a fair shot at snow before the day is done.

Just watching the radar waiting to see when the line pluses back up again...

[SP1986]

Not much wind here yet, we may not get the wind here until the squall arrives. It should be just a little breezy here, until evening.

[Liam J]

Irish meto pressure chart also has the pressure lower than the GFS, this fits more inline with the NAE, nasty little feature taking shape quite rapidly.

Also of note it will continue very windy through Tuesday, with gales affecting many Northern and western areas gusting over 60mph in places.

Edited October 17, 2011 by Liam J

[Liam J]

Having a look at the weather obvs, Finner in NW Ireland is reporting light rain snow on the 11am report.

Very windy over SW Ireland signs of the Low coming ever closer.

Edited October 17, 2011 by Liam J

[The PIT]

All quiet hear but if you look on XCweather you can see that it's livening up over SW Ireland. Earlier signs of a squall line have now disappeared in the last few hours I presume this will form after the low tracks across. Met Office have update the warning for heavy rain and now say becoming very windy rather than windy. I guess they're not sure about the possible gust size yet.

[I Cumbria Marra I]

Wouldnt be surprised if its already reached 55mph

[Richie V]

Wind really increasing here now. Still only gusting 26Mph but thats a big increase from 4Mph half an hour ago.

[Liam J]

Very windy here with some strong gusts coming through now.

[SP1986]

Still no wind here really, we did get a rain shower go through before it did bring with it a gust, but winds really no stronger the 9mph. This is because Wales is protecting us from the SWlys though, I'll have to check out the updated Met-office.

[Aaron]

Quite windy here too, gusting to 37 mph

Pressure is also falling rapidly

Edited October 17, 2011 by Aaron

[Snowynorth]

I think the squall will increase in severity as it crosses the irish sea with the cold air behind mixing with the warmer sea water. Thats when the fireworks will start i think !!!!

[SP1986]

I've just seen the updated METO warning, it has now increased to include coastal areas of NW England and North Wales now. That said I don't think there will be any reason to warrant changing the 'be aware' to 'be prepared/take action', as I think the METO have pretty much covered it all without the need for superceding warnings.

[Richie V]

I've just seen the updated METO warning, it has now increased to include coastal areas of NW England and North Wales now. That said I don't think there will be any reason to warrant changing the 'be aware' to 'be prepared/take action', as I think the METO have pretty much covered it all without the need for superceding warnings.

Something tells me they should mabe issue a severe gale warning for all of northern England.

[SP1986]

To be fair, I don't think at the current time this is affecting all of Northern England. It will probably take a few hours and some meticulous tracking, to ascertain the damage that the squall line could do, it could be problematic, but for now, wind is generally only affecting coasts, hills and exposed parts (including downwind of the Pennines) in true Northern England (which is pretty typical of such a setup)

[Liam J]

Severe gales over western Ireland, a circulation can be picked up over Ireland with cyclonic winds circling round the depression centre.

[The watcher]

The rainfall here has been going for an hour or so, but nothing heavy as of yet, we seem to be tantalisingly close to the edge of the intense rainfall. Winds so far are pretty much non-existant. The band seems to be VERY slow on this end.

[Lancashire Lass]

Pressure falling quickly at -1.3hpa/hr

Winds have increased ever so slightly but nothing dramatic as of yet.

Edited October 17, 2011 by Lancashire Lass

[P-M]

Winds are increasing now some nice gusts coming through although nothing serious, just noticably windier!