CONVECTIVE FORECAST
VALID 11Z SUN 20/04 - 06Z MON 21/04 2003
ISSUED: 20/04 10:32Z
FORECASTER: GROENEMEIJER

GENERAL THUNDERSTORMS ARE FORECAST ACROSS PARTS OF FRANCE, NORTHWESTERN ITALY, NORTHERN IBERIA AND SOUTHERN PARTS OF THE BRITISH ISLES

SYNOPSIS

A WSW JET IS LOCATED OVER THE MEDITERRANEAN. A SHORTHWAVE OVER IBERIA WILL MOVE EASTWARD DURING THE PERIOD. A COMPLEX UPPER LEVEL LOW IS LOCATED OVER THE BRITISH ISLES, WITH A CENTER WEST OF BRETAGNE SLOWLY MOVING TO THE SOUTHERN BRITISH ISLES. A TROUGH OVER THE SOUTHERN NORTH SEA IS MOVING NORTHWARD. A HIGH PRESSURE SYSTEM IS LOCATED OVER EASTERN SCANDINAVIA. AT LOW LEVELS, A SOUTHERLY FLOW ADVECTS HIGH THETA-E NORTHWARD. WARM FRONT AT THE EDGE OF THE WARM PLUME WILL MOVE NORTHWARD FROM CENTRAL FRANCE TO THE BENELUX COUNTRIES DURING THE PERIOD. SOME STORMS MAY FORM IN THE SLIGHTLY UNSTABLE AIR MASS NEAR THE FRONTAL ZONE AIDED BY DIURNAL HEATING. ALSO SOME STORMS ARE EXPECTED NEAR THE UPPER LEVEL LOW OVER THE SOUTHERN BRITISH ISLES.

DISCUSSION

...NORTHWESTERN ITALY...
INSTABILITY WILL BUILD AHEAD OF APPROACHING SHORTWAVE CURRENTLY OVER EASTERN IBERIA. STORM COVERAGE WILL INCREASE OVER THE AREA DURING THE PERIOD. NEAR PASSAGE OF THE TROUGH, MID-LEVEL WINDS NEAR 50 KNOTS WILL OVERSPREAD THE AREA. IN COMBINATION WITH WEAK SOUTHERLY SURFACE WINDS, THIS WILL LEAD TO DEEP-LAYER SHEAR MARGINALLY SUPPORTIVE OF SUPERCELL CONVECTION. THERE IS A SMALL CHANCE OF LARGE HAIL WITH THESE STORMS. LOW LEVEL SHEAR IS SMALL...SO CHANCE OF TORNADOES IS QUITE LOW IN SPITE OF LOW LCL HEIGHTS.

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