16th Aug 2011 - Storm/convective Forecast Discussion And Reports

[Coast]

Please post in here with your convective discussion for 16th August.

Netweather forecast out:

Click for full size

Valid: 16/08/2011 00:00 - 17/08/2011 00:00

Headline: ...THERE IS A RISK OF THUNDERSTORMS FORECAST...

Synopsis

Large cyclonic flow around upper low centred over Iceland dominates NW Europe during Tuesday with a shotwave trough moving ENE across Nern Britain during the day ... at the surface - low expected over W Ireland at 00z Tues will move ENE to be centred over Sern Scotland at 12z Tuesday, with a wrap around occlusion and cold front trailing S to Sern England.

... EIRE, SERN SCOTLAND and N ENGLAND ...

Upper short-wave trough currently west of Ireland, with associated surface low on its forward side, will move ENE across N Ireland early Tues and later across Scotland and N England. Large scale ascent of warm moist Tm air wrapping up into low circulation will result in elevated convection initially across Eire and later Scotland during Tues morning - convection maybe deep enough to support isolated lightning. Into the afternoon, if cloud breaks occur, insolation may lead to scattered more surface-based t-storms developing across Sern Scotland and N England. With up to 30-40 knts of deep layer shear available, storms may organise with a risk of strong wind gusts, hail and torrential downpours with a risk of localised flooding. Some low-level shear is also indicated, as the low moves through S Scotland, so an isolated tornado can't be ruled out - especially over NE England - though overall risk of severe weather seems too low to warrant a slight risk for now.

Issued by: Nick F - Forecaster for Netweather

[Coast]

Storm Forecast

Valid: Tue 16 Aug 2011 06:00 to Wed 17 Aug 2011 06:00 UTC

Issued: Mon 15 Aug 2011 23:00

Forecaster: KOROSEC

A level 1 was issued for central Sweden mainly for strong wind gusts, brief funnel/tornado and locally excessive convective rainfall.

A level 1 was issued for the Baltics, extreme NNE Ukraine, E Belarus into W Russia mainly for excessive convective rainfall, large hail and strong wind gusts.

SYNOPSIS

A ridging pattern is establishing across the south-central Europe and a long-wave trough over NE Atlantic sea. A weak short wave trough moves across the Baltic sea/States. A frontal system affects central Sweden and Norway. Still low geopotential heights affecting eastern Europe/western Russia with mostly daytime driven activity. Elswhere, developing heat wave with strong capping preclude deep convection except some isolated storms near the local complex topography over Italy and S Balkans. A SFC front continues to weaken while moving across the central Balkans with almost no shear and only marginal instability available, so severe activity is unlikely there.

Areas Affected:Eastern Scotland and Eastern England

Synopsis:

An area of low pressure in association with a marked upper trough is expected to move across the UK during the day, with its associated frontal systems bringing areas of dynamic precipitation to a large portion of the country, but particularly across northern regions.

Discussion:

Starting the discussion with the majority of the UK and many areas are at little or no risk of experience any significant convective activity through Tuesday. Frontal cloud is expected to bring some extensive light or moderate, locally heavy rain, particularly across western up-slopes of Northern England and Scotland. Precipitation is expected to be mainly light or moderate across southern areas with little significant precipitation expected. Also a clearance is expected across Ireland during the afternoon and evening in association with NVA and subsidence with some prolonged bright or sunny spells developing before dusk.

The slight risk of Eastern Scotland and Eastern England has been issued in association with the risk of some potential instability during the course of Tuesday afternoon and perhaps into the early evening. Despite extensive frontal cloud and also dynamic, frontal precipitation, there is a signal from some of the forecast models for potential instability. The GFS, UKMO MESO and particularly the WRF and ECM models do signal the potential for 200 to 400j/kg of MLCAPE, primarily from a zone of potential instability between 700mb and 400mb. Surface temperatures of around 17C and 18C coupled with dew points of around 13C or 14C may well be enough to create a completely unstable environment across eastern Scotland and England during the afternoon.

There is a marked region of DPVA moving east across the UK tomorrow in association with the mid-level trough and with also marked NVA following on behind. This zone of DPVA could also be a focal point in aiding the development of convective activity embedded within the broader zone of frontal precipitation. There is a clear signal from the forecast soundings analysed for potential instability during the course of Tuesday afternoon and hence the slight risk level. There is also some well established DLS in particular with 0-6KM of 20KT to 30KT across Northern England, but with lower shear across Scotland. Also of interest, which again lends a hand towards potential instability is a zone of theta-w heading west to east in association with the surface low and its frontal zones during Tuesday afternoon.

The above variables do signal a risk of perhaps some localised embedded convective downpours developing either within the broader zone of frontal precipitation or perhaps just to the rear of the frontal zones. Isolated or perhaps scattered thunderstorms may develop, but this synoptic situation is often particularly fickle and despite all the above ingredients the outcome may well nothing of significance. Given some DLS, reasonable amounts of helicity and low LCL heights it is also prudent to highlight a low risk of funnel clouds and perhaps a tornado, particularly in direct association with the eastward moving cold front and zone of high DVPA.

Best of the CAPE starts developing later into the day:

Looks to be a slim chance of something on the Scottish borders and upwards on the North East coast maybe this afternoon, but not holding out a lot of hope TBH

[Staffordshire]

Ahhh so the usual areas...

[Coast]

Ahhh so the usual areas...

Or not!!!? Nothing reported, not even a rumble. Everyone must have gone abroad for holiday or it is truly a quiet meteorological day

[Thundery wintry showers]

Some very heavy downpours over Cleadon at the moment with some towering cumulonimbus cells, though no thunder.

[CreweCold]

I see there's a downpour around Newcastle Upon Tyne.......just for a change!

[P-M]

I see there's a downpour around Newcastle Upon Tyne.......just for a change!

Confirmed, torrential downpour but no thunder heard. Clouds Towering though to my west and south.