CONVECTIVE FORECAST - UPDATE
VALID 10Z THU 28/10 - 06Z FRI 29/10 2004
ISSUED: 28/10 11:01Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across Bay of Biscay and western France to southern and central Great Britain

General thunderstorms are forecast across see previous outlook

SYNOPSIS

Intense upper long-wave trough placed over western and northwestern Europe, yielding a deep southwesterly flow from northwestern Africa to Alpine region and further to Baltic Sea region, while upper ridge is present over southeastern Europe. At lower levels ... relatively unstable maritime airmass will spread southeastward in the range of eastern Atlantic storm system.

DISCUSSION

...Bay of Biscay, western France, Great Britain...
Very strong upper vort-max indicated by dark stripe on latest water-vapor images propagates NE-ward over the Bay of Biscay ... reaching western France and southern Great Britain during the day. To the east ... an airmass characterized by rather rich low-level moisture and neutral to slightly unstable lapse rates is advected northward into Great Britain. Strong linear forcing should be sufficient for thunderstorms as CIN will remain quite low. With more than 25 m/s deep layer wind shear ... organized convection will likely develop. Expect that one or two well developed convective lines will form and merge into a comma cloud later on ... moving NNE-ward into central Great Britain. Severe wind gusts will be the main severe threat. Over western France ... and southern Great Britain ... latest model output suggests that high low-level SRH values and low LCL height will be present, and chances for tornadoes should be significantly enhanced. Isolated large hail and (probably widespread) convectively induced severe wind gusts are forecast.

...other regions...
see previous outlook

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