Convective Outlook

[Coast]

Please discuss up and coming convective possibilities in this thread. Other storm threads may be running where it is appropriate to discuss general high winds, excessive rain / flooding or Atlantic lows. We also have a dedicated report section where you can post your storm reports.

[Coast]

Convective forecast out from Netweather: forum.netweather.tv

Last nights late ESTOFEX forecast still in effect:

Storm Forecast

Valid: Wed 25 Nov 2009 06:00 to Thu 26 Nov 2009 06:00 UTC

Issued: Tue 24 Nov 2009 23:00

Forecaster: PUCIK

A level 1 was issued for England, Northwestern France, BENELUX, N Germany, Denmark, SW Sweden mainly for tornadoes and severe wind gusts.

A level 1 was issued for Ireland mainly for tornadoes and to the lesser extent, marginally severe wind gusts.

SYNOPSIS

The major feature on the weather maps is a large cyclone over the Eastern Atlantic, which is expected to reside over the area also during Wednesday. On the forward flank of the cyclone, a southerly strong mid and upper level jet is observed with windspeeds over 50 m/s from 500 to 300 hPa layers. Jet will gradually weaken during the day as the cyclone slowly spreads eastwards. Ahead of the cyclone, a ridge will retreat to the east with its axis stretching from the Mediterranean to Central Europe and Scandinavia around 12 UTC. At the surface, center of the cyclone will cross Northern Scotland with pressure under 960 hPa and then turn northeastwards. At 06 UTC, surface cold front will be passing the British Isles and during the day we expect that it will have passed BENELUX and much of France and Germany.

DISCUSSION

...England, Northwestern France, BENELUX, N Germany, Denmark, SW Sweden...

Strong cold front will make its way across the region. Ahead of the front, very strong flow will be present, veering from southerly to south-southwesterly direction with height. At 925 hPa windspeeds above 20 m/s are anticipated and at 500 hPa, values will vary between 40-50 m/s. Models are predicting a belt of enhanced SREH values both in 0-1 and 0-3 km layer. Due to the above mentioned facts, favorable kinematic setup is in store with wind shear values above 40 m/s in 0-6 km layer and from 10-15 m/s in 0-1 km layer.

Strong mesoscale ascent is anticipated in the frontal region and high PV values are advected at upper levels behind the front. One of the detrimental factors to the situation will be a lack of well-developed latent instability. Both GFS and ECMWF predict very marginal values of CAPE, around 200 J/kg in the vicinity of the front. But frontal ascent can at least a bit compensate for the instability. There is a slight chance that with strongly forced convection, meso or misocyclonic circulations manage to develop with attendant threats of severe wind gusts and tornadoes. Due to these threats, Level 1 is issued.

... Ireland, Northern Ireland, Wales, Western England...

In the post-frontal environment, cold mid-levels combined with relatively warm SSTs lead to the marginal destabilisation of the maritime polar airmass. CAPE values around 500 J/kg are expected, mostly over the sea, but models simulate certain values of CAPE also inland. Due to the strong flow at lower levels of troposphere, strong windshear at 0-1 km is forecast, with values up to 15 m/s. Enhanced SREH is also simulated, due to the ageostrophic flow component due to the friction. Slight chance of tornadoes will exist as well as marginally severe wind gusts with stronger convection

As is TORRO's:

TORRO TORNADO WATCH 2009/013

A TORNADO WATCH has been issued at 17:15GMT on Tuesday 24th November 2009

Valid from/until: 18:00 - 12:00GMT on Tuesday 24th/Wednesday 25th November 2009, for the following regions of the United Kingdom & Eire:

Parts of (see map)

All of England and Wales Channel Islands

THREATS

Tornadoes; wind gusts to 70mph; hail to 15mm diameter; CG lightning (hail/lightning post-cold front)

SYNOPSIS

Strong cold front will move east/south-east across the area tonight. Whilst deep convection is not expected along the front, strongly-forced shallow convection is simulated, with a good chance of LEWP/bowing segments, and misocyclone development. Such development brings the risk of wind gusts of 60-70mph, and short-lived tornadoes. There is a chance of a number of tornadoes overnight.

Tomorrow morning, one or more post-frontal short-wave troughs is expected to race eastwards, especially (but not exclusively) across southern parts. If convection fires on these, hail/thunder/strong winds and (perhaps) tornadoes will be possible - indeed, a stronger tornado (T4) is possible should this convection develop.

The major driving trough is expected to move across late morning into the afternoon. The watch may need to be extended/re-issued at 1200GMT tomorrow.

and the charts show:

Another morning to keep you on your toes!

[maidstone weather]

much of the UK at risk apart from eastern counties of England perhaps?

Storm Forecast Issued: 2009-11-24 19:47:00

Valid: 2009-11-24 23:00:00 - 2009-11-25 22:59:00

Regions Affected

All of the United Kingdom (excluding eastern England, which is included in the WATCH)

Synopsis

A very deep area of LOW pressure located to the north of Scotland will dominate the weather on Wednesday. A cold front will clear eastwards across England from the very start of this forecast period until 07z. Strong squally winds are expected to accompany the cold front, however limited cloud heights is likely to limit the amount, if any, of electrical activity. Conditions appear very favourable for a moderate or strong tornado to develop along the cold front, which may cause significant damage.

Behind the cold front, frequent showers and thunderstorms, with hail at times, will plague southern and western coasts, moving quite far inland at times due to the strong and gusty winds. The showers are likely to align themselves into distinct bands/troughs in places, particularly along southern counties of England. Conditions will remain favourable for the development of a funnel or tornado, locally moderate-to-strong in intensity, should any intense cells develop.

Showers will continue to plague southern and western coasts of the UK through the evening and overnight.

http://ukasf.co.uk/module-Storm/mode-forecast/id-273/

[BrickFielder]

Nice trough crossing the UK which is clearly shown on KNMI's Satellite report.

Much higher cloud tops forecast today.

SBCape forecasts show how instability is limited mostly to costal areas, with cumbria again in the firing line.

The area mostly likely to see storms I think is the south coast and the channel as that trough sweeps through.

[Coast]

The area mostly likely to see storms I think is the south coast and the channel as that trough sweeps through.

I'll have some of that! Cheers Brick

[MAF]

latest from Met Office

Thursday 26th Heavy Rain

There is a moderate risk of severe weather affecting the far southeast of England. Heavy showers, accompanied at times by hail, thunder and blustery winds, are expected to be frequent on Thursday, especially near to the south coast. Rainfall accumulations of 30-50 mm can be expected locally by the end of the day.

Issued at: 1030 Wed 25 Nov

[Guest North Sea Snow Convection]

latest from Met Office

Totally fed up with this!

I hope it all s1ds off into the channel

When is this weather going to give us a break!

[Tom Montalbano]

Hi Coast,

Its looking likely Sussex and Kent will be experiencing some heavy rainfall come Thursday and right over the week-end too.

Initially from troughs enhancing shower activity running in from the Channel, I should imagine SSTs are anomalously high at the moment in the Channel, this will surely aid any convection. We know from past experience that in these sort of set-ups, Sussex and Kent, especially coastal regions, are prone to heavy downpours with thunder likely. I see MAF has just posted an advanced warning from the Met Office for that very scenario.

http://charts.netweather.tv/gfsimages/gfs.20091125/06/33/ukprec.png

http://charts.netweather.tv/gfsimages/gfs.20091125/06/45/ukprec.png

Then into the week-end areas of low pressure are forecast to bring more prolonged rainfall to the area.

http://cirrus.netweather.tv/fax/PPVM89.png

http://charts.netweather.tv/gfsimages/gfs.20091125/06/75/ukprec.png

Certainly something to keep an eye on as river levels must be running pretty high at the moment, I should imagine.

Regards,

Tom.

[MAF]

Hi Coast,

Its looking likely Sussex and Kent will be experiencing some heavy rainfall come Thursday and right over the week-end too.

Initially from troughs enhancing shower activity running in from the Channel, I should imagine SSTs are anomalously high at the moment in the Channel, this will surely aid any convection. We know from past experience that in these sort of set-ups, Sussex and Kent, especially coastal regions, are prone to heavy downpours with thunder likely. I see MAF has just posted an advanced warning from the Met Office for that very scenario.

.....................

Certainly something to keep an eye on as river levels must be running pretty high at the moment, I should imagine.

Regards,

Tom.

yes Tom, and here is Saturdays outlook from Met O

There is a moderate risk of severe weather affecting southern England. A period of heavy rain on Saturday is expected to give locally 25-30 mm. This falling on already saturated ground.

Issued at: 1042 Wed 25 Nov

[Tom Montalbano]

Hi Mick,

Yes, I've seen that too. Certainly a concern for the extreme south-east of the country, if those forecasts are accurate.

Regards,

Tom.

[MAF]

Hi Mick,

Yes, I've seen that too. Certainly a concern for the extreme south-east of the country, if those forecasts are accurate.

Regards,

Tom.

yes mate. but i fear us here in SE20 and SE18 may be too far north to be affected as they will be down along the coastal areas. we shall see :unsure:

[Coast]

Hi Coast,

Its looking likely Sussex and Kent will be experiencing some heavy rainfall come Thursday and right over the week-end too.

Initially from troughs enhancing shower activity running in from the Channel, I should imagine SSTs are anomalously high at the moment in the Channel

Certainly something to keep an eye on as river levels must be running pretty high at the moment, I should imagine.

Hi Tom,

Current SST's for the Channel area are buried in each stations data on this interactive map: www.channelcoast.org and seem to be around 12 to 13 DgC this morning on average. I've not seen the river levels on my way into work at the moment as it's too dark but I might stop off tonight to have a look at the Cuckmere as an example.

It's probably a bit early to start looking at Saturdays charts, but an indication of convective rainfall is starting to emerge for the SE coast:

[Tom Montalbano]

Hi Coast,

I have a vague memory of an event a few years back, possibly around this time of the year. A trough became stationary over the Sussex, Kent area for a couple of days and there were some torrential downpours with thunder, especially toward the coast and if my memory serves me correctly, a report of a tornado along the Sussex coast somewhere.

Do you remember this event?

Regards,

Tom.

[Coast]

I have a vague memory of an event a few years back, possibly around this time of the year. A trough became stationary over the Sussex, Kent area for a couple of days and there were some torrential downpours with thunder, especially toward the coast and if my memory serves me correctly, a report of a tornado along the Sussex coast somewhere.

Do you remember this event?

I do remember seeing a funnel out at sea, disappearing behind the neighbours house but couldn't see the end of it so wasn't sure if it was a true spout (although it was reported as such later. I can't recall exactly when, as I have a terrible memory for dates, but I reckon it was about 5 or 6 years ago.

I have to say, this November is turning into a great storm season. I just hope there's no further loss to life or property.

[Neilsouth]

Small thunderstorm passed to my south! :unsure:

[maidstone weather]

typical! yet another storm passes over Maidstone and Norfolk has nowt.

[Neilsouth]

typical! yet another storm passes over Maidstone and Norfolk has nowt.

I don't live anywhere near maidstone , if you're not talking to me ignore this post!

[maidstone weather]

I don't live anywhere near maidstone , if you're not talking to me ignore this post!

I looked at the sferic plots and radar, the storm clearly went over my house

that's the 5th storm to do so since I moved up here - has Norfolk seen a deficit because I'm pretty sure I carry my own storm shield?

[Coast]

Wow! Lovely intense squally storm - went from bright to very dark over 30 seconds and a very heavy shower followed by pea sized soft hail and strong gusts has finally stripped the last of the leaves from the trees. All over and done with in 2 minutes but the roads on our industrial estate are flooded as the drains struggle to cope.

[maidstone weather]

I think come next Spring/Summer, you'll be in a good location for thunderstorms - generally EA and the SE have the higher frequency of storms annually.

May I ask, which sferic detector are you using?

MetO ATD

I see the trough has fired up some sferics now too, so it could well be storm number 6 for my old location shortly since I move up here.

[Neilsouth]

Huge anvil to my west! , ahh

[Neilsouth]

Lightning!! , to my south west.. The anvil size is incredible for this time of year , i can see another one growing far off to the south probably towards the coast

[Jane Louise]

I looked at the sferic plots and radar, the storm clearly went over my house

that's the 5th storm to do so since I moved up here - has Norfolk seen a deficit because I'm pretty sure I carry my own storm shield?

Awww, maidstone weather, Typical!!I really feel for you and I know how you feel.My storm shield also holds strong no matter where I go .

[MR CB]

Just had a nice proper thundery shower here in Eastbourne - got the shopping home in time! Although its night I got the sense something was coming...couple of lightning strikes...embedded hail...heavy rain and strong gusts under the shower. A taste of tomorrow?

[dave48]

Some embedded Cb's by the look of the radar echoes on this trough moving into the SW, looks to arrive on the west coast of Cornwall some time around 8.