22nd into 23rd Aug 2011 - Storm/convective Forecast Discussion And Reports

[Coast]

Please discuss the prospects for, and any actual convective activity for the period through to tomorrow, in here

[essex coast matt]

Storms in north west france at mo, look like they going to miss the SE, with the main band of rain behind it

[Coast]

OK, looking specifically for today right up until midnight, I'll open a thread later this morning for the 23rd August i.e. from midnight onwards to deal with the threats for the early hours and tomorrow.

Here's the info from the usual suspects:

ESTOFEX have no forecast for today (as of yet) neither do SkyWarn or TORRO. So out of the bigger, dedicated sites it's down to UKASF to explain their thoughts for today -

Forecaster: Dan

Last Updated: 23:12 Sunday, 21st August 2011

Valid: 00:00 Monday, 22nd August 2011 - 23:59 Monday, 22nd August 2011

Areas Affected: SLGT: S Coast, SE + CS England

Synopsis:Intensifying upper trough slowly spreads northeastwards across western France and the Bay of Biscay during Monday. Forced ascent of a very warm and humid airmass will therefore provide the main focus for convective activity.

Discussion:

Little activity to talk about until ~18z. For most of the day, a negatively-tilted upper ridge will provide relatively fine and dry conditions across most of the country, and consequently will surpress convection.

Over France, diurnal heating and widespread northward moisture advection will result in >2000 J/kg MLCAPE and the formation of a surface low. Behind the warm front, significant convection is expected, with numerous thunderstorms likely, capable of producing large hail.

The warm front in question crosses the English Channel during the late afternoon and evening hours, with outbreaks of rain arriving along the south coast 17/18z onwards. Whilst embedded convection is not entirely unlikely due to the nature of the setup, the primary focus for any noteworthy convection, and thus thunderstorms, remains behind the warm front within the warm sector.

Current thinking is thunderstorms ongoing over northern France will begin to cross the English Channel around 22z/23z moving slowly NEwards, primarily from Channel Islands-Portland Bill eastwards. However, they are not expected to make landfall until much later in the night, particularly focussed over SE England.

Since this goes beyond this forecast period, an update will be issued on Monday evening. For now, we go with a SLGT level for isolated lightning possible from embedded convection along the warm front.

I'm going along with this, especially the bold section, today up until midnight looks fairly benign.

21st OWS have the feature starting at the end of this forecast period, which ties in with the above

The Met O interpretation says it stays offshore in this period, but later on this slides up the Channel a little more to the North:

Here it is again, at the Western end of the Channel waiting to slide East:

KO index is good and improves towards the end of the period:

See the CAPE gradually creeping North and remember, this is in the 'dark' hours:

So for today, up until midnight I don't currently see any action of note, but midnight onwards for me is where it gets a little more interesting and I'll look at that in the other thread shortly.

[Coast]

Opening this second thread for the convective threats, (forecasts, reports and discussion) for Tuesday 23rd August starting at midnight through to 23.59 tomorrow.

[Coast]

The period of maximum CAPE and LI for the SE corner is quite small and only in the early hours its seems:

By the middle of tomorrow morning its all gone East:

KO index is not that high for the early hours:

Maybe too far South?

Forecast Skew-T for first tomorrow morning is not encouraging:

The time slot for anything to happen looks to be fairly small, somewhere between midnight and 0400 hrs

But it looks like it will really chuck it down!

Lapse rates are up:

Shear just tickles the coast facing France:

On first viewing, this seems a lot more touch and go then I first thought. BBC South East today did cover it in their breakfast weather report today and said up to 40mm of rain could fall and some of it will be thundery - fingers crossed!

[Coast]

Please note that for midnight onwards through tomorrow, there is a second thread here:

http://forum.netweather.tv/topic/70774-23rd-aug-2011-stormconvective-forecast-discussion-and-reports/

[Coast]

Netweather's own NMM charts show the mid-level CAPE and LI bang over my house in the early hours!

Extended Skew T shows some encouraging figures for the period under review:

Dew-points are up through the night, LI is reasonable but the CAPE is quite low. Surface based readings are nothing special at all.

[Harry]

These setups, especially night time, are generally all about the MLCAPE and less about SBCAPE....

I still don't know what to make of it....the most poignant and disturbing chart, as ever, is the "right mover" chart which is at its peak along, yes you guessed it, N France!! But the most encouraging chart IMO is the MCS propagation chart which is slap bang across the SE quadrant.......

Going to be an exciting and intriguing day, but with disappointment being a distinct possibility

[Stuart]

Last Updated: 23:12 Sunday, 21st August 2011

Valid: 00:00 Monday, 22nd August 2011 - 23:59 Monday, 22nd August 2011

Areas Affected:SLGT: S Coast, SE + CS England

Synopsis:Intensifying upper trough slowly spreads northeastwards across western France and the Bay of Biscay during Monday. Forced ascent of a very warm and humid airmass will therefore provide the main focus for convective activity.

Discussion:Little activity to talk about until ~18z. For most of the day, a negatively-tilted upper ridge will provide relatively fine and dry conditions across most of the country, and consequently will surpress convection.

Over France, diurnal heating and widespread northward moisture advection will result in >2000 J/kg MLCAPE and the formation of a surface low. Behind the warm front, significant convection is expected, with numerous thunderstorms likely, capable of producing large hail.

The warm front in question crosses the English Channel during the late afternoon and evening hours, with outbreaks of rain arriving along the south coast 17/18z onwards. Whilst embedded convection is not entirely unlikely due to the nature of the setup, the primary focus for any noteworthy convection, and thus thunderstorms, remains behind the warm front within the warm sector.

Current thinking is thunderstorms ongoing over northern France will begin to cross the English Channel around 22z/23z moving slowly NEwards, primarily from Channel Islands-Portland Bill eastwards. However, they are not expected to make landfall until much later in the night, particularly focussed over SE England. Since this goes beyond this forecast period, an update will be issued on Monday evening. For now, we go with a SLGT level for isolated lightning possible from embedded convection along the warm front.

http://www.ukasf.co.uk/storm-forecasts/79

[Nick F]

Thundery rain seems more advanced in its northerly extent over France this morning, now spilling over the Channel, so could see some thundery showers arrive across southern counties as early as this afternoon, though the main bulk of heavy thundery rain looks like moving in from the SW around midnight onwards.

Meteociel (the french weather site) mentions the storms across NW France this morning, here's a rough translation of what they say:

Situation at 08:30: sometimes violent storms are already on the front west. They are found in the Maine et Loire and the Sarthe. They are accompanied by strong wind gusts (> 60km / h), hail (diameter unknown) and heavy rainfall (which can sometimes exceed 300 mm / h). Another area of ​​thunderstorms on the Vendée and Loire-Atlantique. They are there, producing a sustained electrical activity, locally hail, strong wind gusts and large rainfall intensities (> 250mm / h locally). These storms back east Breton and Normandy

I suspect these will track NE and stay over France, probably waning during the morning, as storm activity tends to during the middle part of the morning. Main action for us is currently over northern Spain.

.

[MP-R]

Not holding out much hope for anything today or tomorrow - just the wrong type of set up!

All eyes on Wednesday onwards as that trough moves in from the Atlantic with a slight southerly draw around its eastern edge. Some potentially slow-moving thundery downpours/thunderstorms a la 7th August then.

[EML Network]

Looking forward to the prospect of a good storm, we got clobbered at the end of June here in Shoreham By Sea, however, I was at work some 10 miles away when it hit, and missed out.

So I Make Out a 25% chance of seeing a good storm from midnight onwards , through until 4-5am , and a 75% chance of seeing some pretty heavy rain Tuesday morning 6am-10am.

Finally something to look forward to after what has been a mediocre summer at best, May, June, July, and much of August has been quite bland, here's hoping we see a stormy autumn

[chionomaniac]

Thundery rain seems more advanced in its northerly extent over France this morning, now spilling over the Channel, so could see some thundery showers arrive across southern counties as early as this afternoon, though the main bulk of heavy thundery rain looks like moving in from the SW around midnight onwards.

.

The radar is certainly showing two distinct bodies of precipitation now.

The first looks like a warm front and arcs from the south of Kent to the Brest Peninsular - unlikely to see thundery activity here but it is already close to sourthern counties.

The second is the area of interest which looks thundery. This is in the Le Mans region. I will be watching for further storms setting of further north of this behind the warm front and checking the direction of travel - Let's hope that any right turn is delayed!

Are Estofex forecasters on holiday? I know that some days that they don't issue forecasts.

[P-M]

I am LOVING the write up from the MetO for the East of England tonight wish I was there:

Tonight:

Becoming increasingly cloudy with rain moving north, becoming heavy at times with an increasing risk of intense thunderstorms and local downpours, especially in the south. Minimum temperature 14 °C.

[MR CB]

The Channel here looks threatening already - a big CB rolling in with mammatus. Heavy downpour imminent I think...looks good and earlier than forecast looking forward to later this evening.

[Norfolk Sheep]

I am LOVING the write up from the MetO for the East of England tonight wish I was there:

Tonight:

Becoming increasingly cloudy with rain moving north, becoming heavy at times with an increasing risk of intense thunderstorms and local downpours, especially in the south. Minimum temperature 14 °C.

Ooh, what a lovely idea Unfortunately I'm in the north of the region but I would doubt if that actually came off, MetO are notoriously bad at forecasting for the East of England!

[chionomaniac]

Just checked the sky to my south - black clouds rolling in with mid level altocumulus castellanus attached - more promising than I originally thought!

[A.J]

Well, up here in the west midlands, it looks like a few hours of moderate rain and then a day of drizzle is on the cards for the overnight period into tomorrow...I fear the only electrical activity I will see tonight/tomorrow will be when I put the kettle on for a morning cuppa!

[Nick F]

The radar is certainly showing two distinct bodies of precipitation now.

The first looks like a warm front and arcs from the south of Kent to the Brest Peninsular - unlikely to see thundery activity here but it is already close to sourthern counties.

The second is the area of interest which looks thundery. This is in the Le Mans region. I will be watching for further storms setting of further north of this behind the warm front and checking the direction of travel - Let's hope that any right turn is delayed!

I think the current storms over NW France will track NE and stay over France, probably waning over the next few hours - with new storms developing with the the heat of the day this afternoon deeper across France.

Models show the bulk of heavy thundery rain for us will arrive later this evening and overnight from the SW in conjunction with an upper low/trough currently over NW Spain then moving NE towards us, which is bringing storms to northern Spain atm.

[Harry]

I am LOVING the write up from the MetO for the East of England tonight wish I was there:

Tonight:

Becoming increasingly cloudy with rain moving north, becoming heavy at times with an increasing risk of intense thunderstorms and local downpours, especially in the south. Minimum temperature 14 °C.

Hmm...unlike the South East corner where the forecast is for intense downpours and thunderstorms....I prefer the wording for East Anglia albeit the differences are slight

[P-M]

Ooh, what a lovely idea Unfortunately I'm in the north of the region but I would doubt if that actually came off, MetO are notoriously bad at forecasting for the East of England!

Just to be anywhere in the risk zone would suit me lol We have had a load of storms this year but don't think I would ever get sick of them even if I had one every day of the year lol To be honest there's not a massive distance between the north and south of the region (in terms of miles) is there? So, I would be surprised if there were intense storms in the south of the region, if they didn't make their way north to you! lol

[AWD]

My local forecaster isn't expecting nothing thundery in my region!

However it could be interesting for London/SE!!!

Here's his latest tweets from Ian Fergusson

W Country & SW less likely to see t-storm issues tonight, but still lots of uncertainty on rain totals here. UKMO UK4 model still says v wet

It could be a very lively night across SE & London into early hours Tues AM; potential for disruptive rain & lots of lightning there....

[P-M]

Hmm...unlike the South East corner where the forecast is for intense downpours and thunderstorms....I prefer the wording for East Anglia albeit the differences are slight

lol yes that's why I picked that one, but to be honest anywhere in the risk zone would suit me!

[Coast]

It could be a very lively night across SE & London into early hours Tues AM; potential for disruptive rain & lots of lightning there....

Yep, I will probably end up merging today's and tomorrows thread into one later if it is as quiet this side of Midnight as expected. From around 3am onwards should be very interesting!!! (if I can stay awake)

[Harry]

Satellite imagery at the moment is encouraging....lots of clear, drier slots developing around the Low which has helped the current cells to erupt very early on! If these clearer slots remaining throughout the day could make for some, given the very high amounts of juice over France, very explosive thunderstorm development! Let's keep our fingers crossed that it both kicks off big styley and the low is not inclined to swing further East!!!

After the past few days of all out pessimism, the excitement is ramping big style!

PS - I will save Coast the job!