CONVECTIVE FORECAST
VALID 06Z SUN 02/11 - 06Z MON 03/11 2003
ISSUED: 01/11 21:00Z
FORECASTER: GATZEN

There is a moderate risk of severe thunderstorms forecast across eastern central Mediterranean

There is a slight risk of severe thunderstorms forecast across parts of the central and eastern central Mediterranean

There is a slight risk of severe thunderstorms forecast across parts of the British Isles

General thunderstorms are forecast across NWern Europe, western central Mediterranean

SYNOPSIS

Long-wave trough placed over NWern Europe and sharp short-wave trough extending into the western Mediterranean is expected at the beginning of the forecast periode. At the surface ... cold front over the western Mediterranean will move eastward and cross the central Mediterranean during the forecast periode.

DISCUSSION

...Central Mediterranean...
Latest WV satellite image shows well developed amplified short-wave trough over the western Mediterranean extending into northern Africa. Very strong jet streak /up to 100 kts @ 500 hPa shown by LIEE sounding/ at it's eastern edge affects the central Mediterranean during the night, where severe thunderstorms are forecast. Tomorrow ... short-wave trough should weaken and associated jet streak moves northward. At the end of the forecast periode ... the short-wave trough is expected to tilt northward, and synoptic scale lift should affect the eastern central Mediterranean. At lower levels ... east of a propagating cold front over the western central Mediterranean, warm and well mixed airmass originating from the Sahara is situated over central and eastern central Mediterranean. This airmass is characterized by steep lapse rates between 900 and 700 hPa as indicated by today's Trapani 12Z sounding. Underneath the capping inversion, relatively moist boundary layer should be in place over most of the affected region ... where surface dewpoints in excess of 18 C should be possible and CAPE should likely reach values in the order of 1000 J/kg. At the beginning of the forecast periode ... thunderstorms along the surface cold front and in the WAA regime should affect parts of the northern and central Mediterranean and southeastern Balkans. As SELY surface winds are forecast ... strong 0-1km shear in the order of 30 kts and 60..80 kts deep layer shear is expected ... and should assist organized convection like mosecyclones and bow echoes. Large hail, severe wind gusts and tornadoes should be possible ... what warrants a MDT RISK. During the forecast periode ... strong jet streak should move NEward and synoptic scale UVM is forecast to weaken. Additionally, decreasing deep layer shear should reduce severe potential somehow. However ... along the cold front and east of it ... thunderstorms may form and should encounter strong low level shear, and supercells may form with the chance of large hail, strong wind gusts and tornadoes. Severe potential should be significantly lower than the day before, though.

...British Isles...
Underneath the NWern European trough ... relatively warm convectively mixed airmass will enter the British Isles in the range of a cold front. This airmass should possible reach CAPE in the order of some 100s J/kg. Behind the cold front ... cold air advection should be rather weak. Several vort-maxima are embedded in the main trough, and convection should likely develop during the forecast periode along the cold front and west of it. Relatively strong deep layer shear should support organized convection like bow echoes and multicells, and severe wind gusts should be the main severe threat that warrant a SLGT RISK. However ... orographically enhanced SRH values may be favourable for mesocyclones, and large hail and tornadoes are not ruled out ATTM.

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