CONVECTIVE FORECAST
VALID 06Z FRI 10/09 - 06Z SAT 11/09 2004
ISSUED: 09/09 14:47Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across northwestern Spain, central France

General thunderstorms are forecast across most of western Europe, Black Sea region

SYNOPSIS

Well developed omega flow pattern present over Europe ... with a ridge axis reaching from Algeria to Norway. To the east ... northerly upper flow is dominating west of a intense upper trough over extreme eastern Europe. Another upper trough is present over the northeastern Atlantic, yielding a southerly flow over western Europe. At lower levels ... cold airmass has entered Europe east of a line reaching from southwestern Great Britain to central France and western Mediterranean.

DISCUSSION

...Western Europe ...
Warm and unstable airmass is present over western Europe ... with steep lapse rates originating from northern Africa and the Iberian Peninsula advecting northward east of surface low over the gulf of Biscay. Low-level airmass is relatively moist with dewpoint in the range of 14 °C over France ... and GFS CAPE estimates seem to be realistic with several hundreds J/kg on Friday. Furthermore ... relatively strong southwesterly upper flow is present over western Europe ... reaching more than 25 m/s at the 500 hPa level on Friday afternoon over western France. At lower levels ... southerly winds are forecast over the region ... and deep vertical wind shear should reach 20 m/s over northern Spain, western France, and southern Great Britain. During Friday ... a vort max is forecast that should move over France reaching Benelux/northwestern Germany during the evening. DCVA and diurnal heating should weaken the cap and thunderstorms are expected to initiate along a cold front/convergence line moving eastward over France. As deep layer wind shear will be sufficient for organized convection ... multicells and mesocyclones are expected ... capable of producing isolated large hail and severe wind gusts. The thread of tornadoes is enhanced as low-level wind shear will increase over France and northern Spain due to backing surface winds to the north of a forming surface low over Spain. Convection should merge into one MCS during the day that should move NW-ward reaching Benelux, southern Great Britain and northwestern Great Britain in the evening hours.

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