Convective/Storm Discussion

[Coast]

It's going to be an interesting one to watch, but I won't be throwing toys out if it dosen't materialise as hoped for.

GFS shows it could happen any time in the next two days in the SE:

Some of the numbers seem encouraging

Sounding forecasts not quite getting into the sweet spot just yet:

Plymouth

London

Tuesday has it more widespread according to the MetO:

If it does happen Wednesday, it could be confined to a very small strip of the coast:

It will be interesting to see what Nick or Brick have to say tomorrow and the usual dedicated storm sites later tonight. BBC's Carol Kirkwood had a possibility of thunderstorms tomorrow.

If nothing else, there will be a messy lot of rain!

[dogs32]

Just had some info that the Midlands and Glos are or could be in the firing line..

will be keeping my eye on thing's

[Harry]

Just had some info that the Midlands and Glos are or could be in the firing line..

will be keeping my eye on thing's

Sod thunderstorms lol - have you seen what has fired up in the Bay of Biscay - draw attention to NL's new thread on intense surface low - I myself have never seen something so pronounced and defined so close to our shores!

[johnholmes]

I suggest people read the thread all about the tropical storm-plenty of input from various people on there

Edited October 5, 2009 by johnholmes

[Coast]

Grace is starting to make her presence felt:

But is she having a little paddy or a full blown hissy-fit?

[Coast]

At this stage and with possible effects from Grace, I guess the NW storm risk is as good as we can guess/expect:

[Jane Louise]

I'm looking forward to this :

This Evening and Tonight:

This evening and tonight will be cloudy with occasional outbreaks of rain, which could become heavy and thundery at times. It will also become misty with fog over the Moors and some southern coasts. Minimum temperature 13 °C.

http://www.metoffice.gov.uk/weather/uk/sw/sw_forecast_weather.html

[Nick F]

Some thunderstorms ahead in the Tm airmass advecting NE towards UK as it destabilises along frontal boundary across Bay of Biscay:

http://meteocentre.c...en&map=EuropeNW

http://www.euclid.org/realtime.html

Wouldn't be suprised to see some sferics across SW England later tonight and later across Sern Ireland and SW Wales in the morning as shortwave pushes NE.

[dogs32]

looks very heavy down South North Biscay..

Jane might get some lightning after all

[Jane Louise]

looks very heavy down South North Biscay..

Jane might get some lightning after all

I bet I'll be asleep though!! Lol (it'll be sods law that I miss it)

Any idea what time I would see something dogs?(if it actually happens lol)

[dogs32]

I bet I'll be asleep though!! Lol (it'll be sods law that I miss it)

Any idea what time I would see something dogs?(if it actually happens lol)

I dont know Jane....early hrs I reckon towards dawn..just a guess....

Looks like there might be a potentail there anyway....going to charge battery up just in case in video camera...just in case

I wonder if it will be like Plainview :lol:

i couldnt resist....naughty doggy

going back to watch my horror film The Twin Sister's of Texas

Edited October 5, 2009 by dogs32

[azores92]

I bet I'll be asleep though!! Lol (it'll be sods law that I miss it)

Any idea what time I would see something dogs?(if it actually happens lol)

looks like gfs is shying away from the heaviest of the rain being over the midlands and wales, and brings it much further south, across dorset/hampshire way where significant totals are being shown. infact, wednesday nights event is being shown as completely dry across the midlands and wales.

[Jane Louise]

Fingers crossed lol

Regions Affected

Wales, Midlands, East Anglia, Southern England, southern portions of Northern England ( Northern Ireland, southern Scotland and remaining Northern England included in the WATCH )

Synopsis

A complex area of LOW pressure, included ex-Tropical Storm Grace, to the west of the United Kingdom will determine the weather on Tuesday. Due to the extra-tropical characteristics of Grace and it's follower LOW, a very warm and moist airmass is advected across England and Wales during the morning hours. There exists potential for embedded thunderstorms along many different weather fronts across England and Wales. However, the setup is incredibly messy, and a lack of instability may inhibit thunderstorm development. Current thinking is that any thunderstorms that do develop are likely to be fairly isolated, but may pose a threat of a tornado. Any existing thunderstorms present during the afternoon are expected to decrease/decay rapidly during the evening hours. Due to the nature of this setup, convective rainfall appears to be the main severe threat, with local torrential downpours persisting for some time in places, which may lead to local flooding. As the forecast for Tuesday is constantly changing, we will monitor the developments and may issue an update if necessary.

http://ukasf.co.uk/module-Storm/mode-forecast/id-264/

[Rob]

some interesting development ahead with Grace :lol:

[Jane Louise]

I too hope Nick and Brick do a forecast on this one!!

I am now awaiting a forecast from ESTOFEX...please hurry up ESTOFEX !! Lol

[richep]

some heavy showers moving up over devon and cornwall now

[cj114]

Very interesting that this Tropical storm is so close to us. Remembering '87 which was an "old" Hurricaine which hit our shores in the south with no warnings. Well not the met office anyway.

However, it does look like just heavy rain for us with this "storm" thankfully, I would never want to go through THAT again.

The rain is very welcome here in the south, even todays rain has perked up the trees and plants.

I did enjoy the pics of the "eye" earlier, but glad it is being enveloped with another system.

And so to bed, odd that the met have not even mentioned "Gwen" in their forecasts. Or maybe not!

[CardiffStorm]

Estofex have issued a level 1 for us.

Storm Forecast

Valid: Tue 06 Oct 2009 06:00 to Wed 07 Oct 2009 06:00 UTC

Issued: Tue 06 Oct 2009 05:26

Forecaster: VAN DER VELDE

A level 1 was issued for England and NW France mainly for the chance of an isolated tornado.

A level 1 was issued for W Iberian Peninsula for chances of wind gusts, large hail, excessive precipitation and tornado.

SYNOPSIS

A low pressue area near the Faroe Islands moves eastward. The increasing thermal gradient due to colliding warm subtropical airmass advected by a steady SWly flow and a polar maritime airmass should inforce the cold front over Ireland and central UK during the period. The occluded front will drag over western Norway causing intense precipitation. Slight instability will be present over England and NW France, and marginal signals track downstream over the southern North Sea, Benelux, N Germany and Denmark, perhaps partially elevated in nature.

Another low pressure system arrives from the Azores to Portugal later during the period and is filled with an unstable airmass.

DISCUSSION

...S Ireland, England and NW France...

GFS predicted widespread convective precipitation over the eastern Atlantic for yesterday, however almost nothing occurred in reality. Lack of significant quasi-geostrophic forcing or even subsidence may have prevented this, and predicted LFC-LCL differences, which were quite substantial, could have played a role as well. With this in mind, a look at GFS reveals some CAPE over the southern half of the UK and NW France predicted mostly for 9Z-15Z, and now LFC-LCL height difference should be small and initialization easier, while QG forcing is better. Other models also predict a band of rain passing during this period. The cold front may provide additional forcing over Northern England, at the margin of CAPE.

Since CAPE and dynamics seem quite marginal (not very baroclinic situation and absence of the jet), it looks like a low end situation, however there is 15 m/s DLS, 150 m²/s² SREH and >12 m/s LLS predicted, with low LCLs, which in principle could yield cells with rotating characteristics and possibly an isolated tornado. Strong but probably not severe gusts are possible.

If convection is able to develop at the front, it could train parallel to it and augment precipitation sums locally.

[Nick F]

Think the Estofex forecast is a little too optimistic wrt slight risk of severe weather ... expect some isolated sferics along cold front across Ireland and Wales IMO during the day, but profiles look pretty warm and saturated most of the way up in the Tm airmass south of cold front which will limit thunderstorm development away from cold front where there maybe sufficient forced ascent to overcome this.

[Coast]

Estofex have issued a level 1 for us.

Nice if it comes off!!!

UKASF also have the area covered:

Storm Forecast Issued: 2009-10-05 23:07:00

Valid: 2009-10-06 00:00:00 - 2009-10-06 23:59:00

Regions Affected

Wales, Midlands, East Anglia, Southern England, southern portions of Northern England ( Northern Ireland, southern Scotland and remaining Northern England included in the WATCH )

Synopsis

A complex area of LOW pressure, including ex-Tropical Storm Grace, to the west of the United Kingdom will determine the weather on Tuesday. Due to the extra-tropical characteristics of Grace and it's follower LOW, a very warm and moist airmass is advected across England and Wales during the morning hours. There exists potential for embedded thunderstorms along many different weather fronts across England and Wales. However, the setup is incredibly messy, and a lack of instability may inhibit thunderstorm development. Current thinking is that any thunderstorms that do develop are likely to be fairly isolated, but may pose a threat of a tornado. Any existing thunderstorms present during the afternoon are expected to decrease/decay rapidly during the evening hours. Due to the nature of this setup, convective rainfall appears to be the main severe threat, with local torrential downpours persisting for some time in places, which may lead to local flooding. As the forecast for Tuesday is constantly changing, we will monitor the developments and may issue an update if necessary.

TORRO are having a lie-in, but expect something from them mid-morning. Here's the best from the rest:

Bet you wish you were in Spain today eh? :winky:

Expect lots of rain, hope for thunder and the very, very remote chance of a tornado I reckon.

Outbreaks of heavy rain are expected to give 15 mm in 3 hour periods during today. The rain will ease from the north during this evening.

www.meteoalarm.eu - North East, North West, Wales, the Humber and Yorkshire.

[Harry]

The radar is a mess lol - very difficult to pick anywhere out under the masses of rainfall...

Have noticed that rain has been intensifying/merging across southern/south western counties in the last hour - could be particularly wet for the Midlands/parts of EA in the coming hours, depending on of course how heavy the rainfall gets.

[dogs32]

nice torrentail downpour here...no thunder heard

[Coast]

A line of Sferics developed off the coast at Brest in the last 20 minutes

[BrickFielder]

It certainly looks messy today with plenty of cloud cover presently. Whether the meeting of warm subtropic air and polar maritime air at the cold front will intensify the front is questionable since the jet stream is north of the front. Instability also looks rather weak and I always view GFS dewpoints with a little suspicion.

Thetae chart showing the meeting of warm and cold air.

There is a marked convergence zone at the surface at the front which I think will enhance lifting even though this is not really showing up on vertical velocity charts. It should be noted that all instability is just marginally south of that convergence line though.

During the afternoon there is some suggestion of some drier air coming in at mid levels which may act to enhance convection.

The environment does look marginally supportive of tornado development, but low instability puts limits on that potential.

At this point things look rather marginal and we need more information before we can realistically make a call. An embedded severe thunderstorm cannot be ruled out at this point, but looks unlikely to me.

[Coast]

Well one of the many required components, the dewpoint, is looking a little more favourable in Eastbourne, currently at 13.8 DgC and the 008hrs chart shows this more widely:

0830 satellite shows Cb's down to the west and the front coming in with some potential anticyclonic vorticity and/or shear vorticity.

The 012hrs Herstmonceux sounding is as important as ever to get a better feel on today's messy outlook.