Uk Convective General Discussion & Forecasts - May 2012 Part 3

[Jane Louise]

A new thread for today onwards!

UKASF

Areas Affected:

SLGT: C + CS Scotland, Pennines, W + S Midlands, Cumbria

Synopsis:

Strong capping beneath upper ridge will inhibit deep convection, but isolated convection may occur in response to daytime heating and orographic forcing.

Discussion:

As LSTs rise sharply, >1400J/kg CAPE is likely to build up. However, with a distinct lack of forcing and strong capping at 950mb due to a warm nose, primary focus then turns to either convergence from seabreezes, or orographic forcing, or ideally a combination of both. This seems most prevalent around the Solway Firth (Dumfries & Galloway and/or Cumbria), and over the Pennines where seabreezes and topography will play a key part in providing forced ascent and the potential for a few isolated showers/thunderstorms to form, but this risk is considered quite low (10-20%). Initiation time is likely to be quite late in the day once again.

Forecast soundings indicate a qute dry profile, so it is questionable as to how much precipitation such showers could produce. Nevertheless, PWAT >30mm locally combined with very light steering winds means locally a quasi-stationary cell could produce a significant amount of rain over a relatively small area - one to watch, perhaps.

Very week shear not only limits severe potential, but also suggests such showers (or storms) will become poorly organised, but given dry air aloft there could be some hail if any stronger cores can develop.

Several models also indicate high ground W + N of London (Chilterns primarily, and perhaps the Cotswolds) may also have the potential for an isolated sharp shower, but given lack of significant topographic forcing and/or convergence, for now we ignore this idea.

http://ukasf.co.uk/storm-forecasts/172

The Netweather stormrisk:

http://cdn.nwstatic.co.uk/gfsimages/gfs.20120524/00/18/ukstormrisk.png

then there's this:

.

http://131.54.120.150/index.cfm?section=dspViewer&strProductType=Hazards&strProduct=THUNDERSTORM-STANDARD#

maybe a forecast to come from Nick F and Brickfielder later!

Good luck everyone!

[lorenzo]

Missed the fun yesterday evening so hopeful of some similar events today...

Come on pennines do the business !

[Robbie Garrett]

Cold front pushing in from east, should start things off.....from the trough and UK south(cold front) from 14Z, ISOL 3000M +SHRA/+TSRA ISOL CB040-060...

Nothing in the TAFs, but that doesn't stop the odd event... if the cold front can keep going. Sun is burning the mist out here down south, so hopefully something through as a result of diurnal.

Lots of CAPE and -LI

London and other places showing a blob on the high res model.

Edited May 24, 2012 by Robbie Garrett

[Robbie Garrett]

Updated chart...

[Darren Bown]

Just after reading Estofex, has the UK ever been in a category 2 or 3?

After a cloudy (and humid) night, the clouds have cleared to clear blue skies, will be keeping my eyes open today, I have the Pennines around 15 miles to my east.

[Harry]

Just after reading Estofex, has the UK ever been in a category 2 or 3?

After a cloudy (and humid) night, the clouds have cleared to clear blue skies, will be keeping my eyes open today, I have the Pennines around 15 miles to my east.

Not in my experience, certainly not for thundery weather. We might have had the odd 2 for violent depressions but that's about it.

Way back in the mid noughties, Estofex used a different categorisation system of "Thunderstorms", "Slight", "Moderate" and "High" (if I remember correctly). Back on that system we had a few moderates and even the odd High Risk but I'm pretty sure we've not had 2's and 3's since the new system took effect.

.

[VillagePlank]

[London/SE]

I think that all that CAPE is going to go to waste, unfortunately. Surface heating almost certainly will be enough to kick stuff of, but I doubt it will vigorous enough (KI) to produce storms. Even if storms do occur they are likely to be bog-standard stuff (TT)

However, watch out for continental imports post 18z; that is where the severe weather interest is, in my view.

Edited May 24, 2012 by Boar Wrinklestorm

[Lynxus]

Just after reading Estofex, has the UK ever been in a category 2 or 3?

After a cloudy (and humid) night, the clouds have cleared to clear blue skies, will be keeping my eyes open today, I have the Pennines around 15 miles to my east.

Yeah ,

I can remember seeing some reds and purples before. But NOTHING ever came from them if i remember correctly.

We certainly havent have any level3's for a while as far as i know.

[StormChaseUK]

Just after reading Estofex, has the UK ever been in a category 2 or 3?

After a cloudy (and humid) night, the clouds have cleared to clear blue skies, will be keeping my eyes open today, I have the Pennines around 15 miles to my east.

Yes level 2 was over Kent 2005/2006 if I remember roughly, and violent storms did occur.

[A.J]

the 06z GFS & Hi-res NMM models are progging some insane CAPE & Lift values for the midlands today...2000j/kg & -5C lift for my location....A crying shame there's very little in the way of a trigger factor...a strong cap is in place but for parts of the West Midlands the hi-res output is showing some decent surface wind convergence, so just a sniff of something going bang later on in my vicinity

[weatherobsuk]

Foggy as anything here this morning showing that moisture is definitely around but transitioning that to useful CAPE is what's needed now. Being under 2400kj of CAPE last year in Cambs and yet nothing happened as like yesterday goes to show how important the 'trigger' factor is when encouraging TCu/CB activity. Lets hope this persistant cap breaks today.

[VillagePlank]

Triggers will be CZs, sea-breezes, and orographic lift, today. Crucially timing is required for such triggers to coincide with max insolation mid afternoon. As far as I can tell there is no CIN (the cap) today?

Edited May 24, 2012 by Boar Wrinklestorm

[staplehurst]

Just after reading Estofex, has the UK ever been in a category 2 or 3?

After a cloudy (and humid) night, the clouds have cleared to clear blue skies, will be keeping my eyes open today, I have the Pennines around 15 miles to my east.

We had a level 2 for southern UK for a proper thundery breakdown on a cold front jobby on Tue 19th June 2007

http://www.estofex.org/cgi-bin/polygon/showforecast.cgi?text=yes&fcstfile=2007062006_200706190408_2_stormforecast.xml

[Mapantz]

Yet again today, showers/t-storms will be extremely localised. Although the chance is slightly greater than that of the past few days. My attention turns to the south west on Sunday possibly. Showers and maybe some t-storms breaking out there.

[A.J]

Triggers will be CZs, sea-breezes, and orographic lift, today. Crucially timing is required for such triggers to coincide with max insolation mid afternoon. As far as I can tell there is no CIN (the cap) today?

On the NW extra storm forecast there is a cap showing for my neck of the woods, 49j/kg, which does erode as the afternoon wears into the evening before re-establishing during the late evening and overnight period

[Methuselah]

Triggers will be CZs, sea-breezes, and orographic lift, today. Crucially timing is required for such triggers to coincide with max insolation mid afternoon. As far as I can tell there is no CIN (the cap) today?

I think you're right there, mate. As hot and clammy as it is, the overlying air is still, generally speaking, in descending mode...that could all change early next week, however?

[Stuart]

Looking at net weather Rader seem to be a few shap showers in the Highlands

[VillagePlank]

On the NW extra storm forecast there is a cap showing for my neck of the woods, 49j/kg, which does erode as the afternoon wears into the evening before re-establishing during the late evening and overnight period

That might actually be a good thing - CIN that small might be overcome if surface heating is sufficient. In that case you might have a pressure cooker scenario which could, in the event, be vigorous enough for storms for form

[NW Leeds Russ]

Looking at net weather Rader seem to be a few shap showers in the Highlands

Yeh looking at the Ptarmign Cam on Cairngorm clouds are building and I think the skiers better watch their poles don't turn in to lightning conductors..!

www.winterhighland.info/cams/cairngorm-mountain/

[A.J]

That might actually be a good thing - CIN that small might be overcome if surface heating is sufficient. In that case you might have a pressure cooker scenario which could, in the event, be vigorous enough for storms for form

my thoughts exactly...fingers crossed!

[Mapantz]

Crazy 18.8°C dewpoint here, all that potential going to waste lol

[Darren Bown]

So difficult to see but I can see cumulus clouds bubbling up above the haze to my NE.

[VillagePlank]

Almost certainly the Pennines orography.

[DubWeatherAddict]

Looks like things are about to go pop over there looking at sat 24!

[NUT]

Bit worried the fact that there does seem to be less cloud around than yesterday at this time but I know if it going to go it could happen anytime................