Valid: 20/08/2010 00:00 - 21/08/2010 00:00
Headline: ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FORECAST...
Synopsis
Upper/surface low to the NW of Ireland on Friday will drive a cyclonic SW flow across the UK, with a cold front lying Peterhead - Middlesborough - Plymouth at 12z moving east with sfc low lying N of Scotland by midnight, while cold front develops wave from the SW as it moves across S England.
… EIRE, WALES, W MIDLANDS, N ENGLAND and S SCOTLAND …
Warm moist airmass advecting NE with high theta-w values (wet bulb potential temps of 16C+) may destabilise with an isolated t-storm or two possible across Wales and Ireland tonight as forcing increases with arrival of cold front and shortwave trough from the SW. Any storm may pose a risk of an isolated strong wind gust and torrential rain with localised flooding.
During Friday, CAPE is modelled to increase ahead of cold front across parts of Wales, W Midlands and N England ... therefore convection may develop with approaching cold front from the W by midday over these areas with a few thunderstorms possible. Any storms that develop will benefit from 30 - 40 knots of 0-6km deep layer shear ... so organisation into multicell/line segments may occur with threat of strong convective wind gusts to 45-50 knots. Strong 0-1km low-level shear up to 30-35 knots is also modelled to develop as winds back ahead of approaching cold front, so there may exist risk of an isolated tornado - if a strong storm with rotating updrafts can develop ... though this could be restricted somewhat by cloud cover/lack of insolation to develop enough instability. However, will issue a SLIGHT risk for parts of N/E Wales and N England given favourable severe kinematics and potential instability.
Thunderstorms will also be possible in the morning and early afternoon across Eire and Scotland post cold front, again with a risk of strong convective wind gusts and an isolated tornado, given strong deep layer and low-level shear in place. Credit Nick Finn from Netweather