Uk General Convective Discussion & Forecasts, 24th August '12>

[Stuart]

Synopsis:

Upper trough to the west of Ireland, with a few shortwaves running northeastwards across Ireland/western Britain on the eastern flank of trough. Some weak convection expected here.

Discussion:

The occasional sferic is possible through the early hours of the morning along Irish Sea coasts, but due to the sparse nature and short time window, we have omitted the SLGT area here.

Else, main focus is over Ireland, Northern Ireland, SW/W Scotland and the IoM where there may be potential for some convective activity. A few hundred J/kg CAPE will allow showers and a few thunderstorms to form in an environment with 30-40kts DLS, of which the majority is in the lowest km.

As a result, a weak tornado cannot be ruled out, and with dry mid-levels, there may be some hail in any stronger cells, potentially up to 2.0cm in diameter. Main concern is fairly saturated upper layers indicated in forecasting soundings, which may lead to excessive high cloud, and limiting surface-based convection depth somewhat. ELTs down to -25C might just be capable of some sporadic, well-scattered sferic activity, but this isn't expected to be widespread.

Showers are also possible over SW Eng during the afternoon, drifting northeastwards into the Midlands. Again, relatively shallow convection will limit sferic activity significantly, and the risk here is considered too low for a SLGT area.

http://www.ukasf.co.uk/storm-forecasts/217

[IanR]

we are usually too far west here in many thundery setups , but in these situations too far east, this really is no mans land for thundery activity,

Edited August 27, 2012 by Rybris Ponce

[IanR]

that should read many thundery setups, editor not working for me

[Chris W]

Nothing tonight but little was expected. I just thought I would share a video I just watched of a phenomenal night time storm over Florida, viewed from a plane - I have seen many videos of lightning, but nothing like this:

[Coast]

ESTOFEX level 1 again today:

Storm Forecast

Valid: Tue 28 Aug 2012 06:00 to Wed 29 Aug 2012 06:00 UTC

Issued: Mon 27 Aug 2012 21:58

Forecaster: KOROSEC

A level 1 was issued for western UK mainly for strong to severe wind gusts.

SYNOPSIS

Ridge builds up from Mediterranean towards central Europe while a trough over western Europe affects parts of SW Europe and UK. A baroclinic zone stretches from central Iberia NE-wards into France. Another trough over eastern Europe gradualy weakening while moving east into western Russia.

DISCUSSION

... western UK ...

Beneath the western European trough, a rather deep surface low slowly moves towards western UK with a frontal system. At least marginal instability will be in place once the quite cold mid levels overspread the region. Some storms might form and enhance threat for some strong winds across Ireland given the quite strong wind field around the cyclone. A marginal level 1 has been issued to cover this potential threat

UKASF also have:

Synopsis:

Upper trough to the west of Ireland, with a few shortwaves running northeastwards across Ireland/western Britain on the eastern flank of trough. Some weak convection expected here.

Discussion:

The occasional sferic is possible through the early hours of the morning along Irish Sea coasts, but due to the sparse nature and short time window, we have omitted the SLGT area here. Else, main focus is over Ireland, Northern Ireland, SW/W Scotland and the IoM where there may be potential for some convective activity. A few hundred J/kg CAPE will allow showers and a few thunderstorms to form in an environment with 30-40kts DLS, of which the majority is in the lowest km.

As a result, a weak tornado cannot be ruled out, and with dry mid-levels, there may be some hail in any stronger cells, potentially up to 2.0cm in diameter. Main concern is fairly saturated upper layers indicated in forecasting soundings, which may lead to excessive high cloud, and limiting surface-based convection depth somewhat. ELTs down to -25C might just be capable of some sporadic, well-scattered sferic activity, but this isn't expected to be widespread.

Showers are also possible over SW Eng during the afternoon, drifting northeastwards into the Midlands. Again, relatively shallow convection will limit sferic activity significantly, and the risk here is considered too low for a SLGT area.

Looks like it could be later int he day if anything happens:

Over Western Ireland mainly?

[Coast]

Looking like Ireland will start to see that action tomorrow before a quiet spell:

Spreading into all of Western UK:

Big blue lined area of tornado chances:

Looks like a good day for potential storms through out Western areas:

Then spreading East:

[Stuart]

Thanks Coast I keep my eyes on them

[Convective]

Hey everyone, hope you had a nice bank holiday. Just wanted to ask a question to an expert or someone that's a bit more clued up than me.. basically, when storms leave the coast of eastern Ireland and head towards us over here on the Isle of Man, they die off when they get about 20 miles off. I am pretty sure this is due to the low sea temperature but if the CAPE and LI is great enough, could a storm sustain over here or will they still die off? Just looking at tomorrow here and look at the CAPE and LI at 4pm!!

[The watcher]

Really fancy my chances tommorow for first overhead storm. Nice little convergence line over my area between 3-6pm running NE into Western Scotland.

[Andy Bown]

Quite surprised at the lack of posts regarding tomorrow.

In fact it could become a very busy day although not so widespread as Saturday.

The BBC Points West forecaster Ian Fergusson showed embedded thunderyness within the main band of rain tomorrow morning, with no

one area favoured - rather a risk just about anywhere in the West Country. I'd suggest this risk could increase further as the front moves

Eastwards into areas that would have had a bright/warm start to the day.

Following the main front there look set to be scattered thundery showers which could be pretty potent where they do occur given the

likelihood of good sunshine late morning/early afternoon to give warm temperatures.

[Chris W]

I checked the Met Office earlier and their map for NW England/West Midlands/NE Wales area was showing thunder symbols widely for tomorrow, added to their yellow warning and tasty looking precipitation map. August usually delivers something if any month will, so let's have it!

On another note (a repost from the NSC) does anyone remember August 2005 storm-wise? I was in Sunderland at my parents' shop then and saw the most ferocious UK storm I have ever seen. I looked outside at some time after 5pm and was astonished to see a pitch black sky with the street lights on - then from the first flash there were strikes every 1-2 seconds for something between half an hour and an hour with torrential rain seriously flooding the adjacent roundabout (and nearly the shop). The sky was being continuously lit up. The next morning we discovered that 100,000 homes in the area (possibly a broader one than just Sunderland) had been without power and there were fires, which was no surprise as strikes were regularly hitting buildings.

I posted the latter as if anyone does recall the event I'd love to know its nature and what caused it. To save cluttering up this thread feel free to message me if you wish to. Having searched around a little I found the following link describing a "supercell" on 31st August 2005 - though I'm not entirely sure which date my storm was on this could very potentially have been it (I do remember hearing of the Metro line being struck):

http://www.neforum2....d762b2f9-2.html

Edited August 28, 2012 by Chris W

[Stuart]

Synopsis:

A mature surface low migrates eastwards under an upper trough, becoming elongated and multi-centred. Widespread showers and thunderstorms are forecast to develop beneath the upper trough, behind an eastward-moving occlusion.

Discussion:An occlusion will move eastwards (and northwards) across much of Britain during the day, becoming rather fragmented across England. Here, with jet aloft creating 60kts DLS, some line convection/convective elements are possible. Dry air intrusion in the mid-levels, combined with backed surface winds and up to 30kts LLS could lead to bowing segments capable of producing a tornado and/or strong wind gusts. With such saturated profiles, lightning activity, if any, is more likely on the back edge where the dry air intrusion is most pronounced.

In the wake of the front, cold mid-levels (-21 to -23C at 500mb) will overspread much of the British Isles and Ireland, steepening lapse rates substantially. As such, diurnal heating will allow 600-1000J/kg CAPE to be available, with widespread showers and thunderstorms expected to develop.

A few shortwaves will move anticlockwise around the low's periphery, providing an increased focus for shower/storm initiation (primarily NW Eng and W Ireland) with the general steering winds allowing such showers/storms to migrate to the east. Low-level convergence across Scotland and Ireland will also help shower/storm development and organisation, primarily due to proximity to the low's centre, and/or convergence on the trough axis.

Cold and dry air aloft, combined with local strong updrafts, could produce some moderately-sized hail in any stronger cells, potentially up to 3.0cm in diameter. Slow storm motion over Scotland and northern portions of Ireland/Northern Ireland, combined with backbuilding, significantly increases the threat of local flash flooding. Given this criteria, this is borderline SVR in terms of it's impact, but such an event is likely to be quite localised. Currently we are unable to pinpoint any region most at risk (out of Scotland and Ireland/Northern Ireland) but an upgrade to SVR may be necessary on Wednesday to accomodate this risk.

Perhaps attention should also be given to southern Ireland (Munster in particular) during the late afternoon/evening hours where an increase in LLS may allow any showers/storms there to become better organised and may perhaps exhibit supercellular-characteristics, capable of producing a tornado.

http://www.ukasf.co.uk/storm-forecasts/218

[Cloud 10]

Already a few strikes from the rainband and showers over in SW Ireland.

Yet another "interesting"convective day coming up tomorrow.

[Chris W]

My workplace is in the moderate zone and my home not too far from it, excellent .

[Jane Louise]

New thread here folks.

http://forum.netweather.tv/topic/74278-uk-general-convective-discussion-forecasts-28th-august-12/#entry2359334