Storm Forecast
Valid: Thu 04 May 2006 09:00 to Fri 05 May 2006 06:00 UTC
Issued: Thu 04 May 2006 09:19
Forecaster: GROENEMEIJER/GATZEN

SYNOPSIS

A well-developed omega flow pattern is present over Scandinavia ... with short-wave troughs over eastern Europe and eastern Atlantic Ocean / Iberian Peninsula. While Atlantic trough remains quasi-stationary ... the shortwave trough over the Iberian Peninsula moves southeastward. At lower levels ... a rather cool and dry air-mass is present over eastern and northern Europe in the range of the omega high. To the west ... a tongue of warm air covers the Iberian Peninsula, France, the western Alps and the British Isles. Latest soundings indicate steep lapse rates and relatively poor low-level moisture ... but moisture should increase underneath an inversion during the day.

DISCUSSION

British Isles

On the western flank of high pressure over north-central Europe a rather strong southerly jet is present over France/British Isles.

00 UTC sounding from Herstmonceux and 06 UTC from Larkhill show that low-level mixing ratios of around 9 g/kg are present under steep lapse rates between 900 and 700 hPa. Strong insolation over much of Great Britain should enable siginifcant surface based CAPE of up to around 1000 J/kg to form. Convective initiation is expected during the early afternoon across southwestern parts of Britain and across Wales.

About 20 m/s bulk shear should be present across most of western England, Wales and Scotland and shear in the lowest 3 km is particularly strong.
This suggests that the formation of a couple of supercells and well-organized multicells is likely.

The storms should be capable of producing large hail and damaging winds. Additionally, a significant threat of tornadoes will exist, given the strength of 0-3 km shear and clockwise turning of the winds with height in combination with strong low-level buoyancy. Tornadoes are most likely with storms that have not yet organized into larger linear systems... something that is expected to occur rather quickly after storm initiation.

During the evening hours, one or two MCS's with a main threat of damaging winds is expected to progress northeastward across northern England and Scotland.

An upgrade to level 2 may be given for parts of the level 1 area in the course of the afternoon.