CONVECTIVE FORECAST - UPDATE
VALID 14Z MON 01/12 - 06Z TUE 02/12 2003
ISSUED: 01/12 15:54Z
FORECASTER: GROENEMEIJER

There is a slight risk of severe thunderstorms forecast across extreme southeastern France, the extreme western part of the Italian Gulf of Genua.

General thunderstorms are forecast across the southwestern and southern UK, western France and across the northern, and western coastal zone of Iberia, southeastern France and the western part of the Gulf of Genua, the Aegean Sea and southern and southwestern Turkey.

SYNOPSIS

An elongated trough centered around 5 WL is transforming into a cut-off low moving southward to the central Iberian peninsula. Filled with a cold air-mass, this system creates some marginal latent instability over the Atlantic waters. To the east...in a strong southerly flow a stagnant N-S oriented frontal zone is located from near the Baleares to southeastern France to the Channel Region. A ridge dominates the weather over south-central Europe and the northern Balkans, causing stable conditions. A high-pressure system at low, mid- and upper levels is located over west-central Russia creating subsidence and stable conditions in that area as well. A weak upper low over the southern Aegean Sea is slowly moving eastward while becoming even less significant. Some marginal latent instability provides energy for scattered thunderstorms.

DISCUSSION

...extreme southeastern France, the extreme western part of the Italian Gulf of Genua....
Some slight latent instability... 400 J/kg CAPE was observed in Nimes at 12Z... and rising motions, have set the stage for thunderstorm development in the lower Rhone Valley over the last few hours.

A strong low-level flow on the warm (eastern) side of the frontal zone (40 - 55 kts at 850 hPa) yields quite high low-level shear (20 - 30 knots 0-1 km shear). In combination with quite strong deep-layer shear (50 - 60 kt), this will possibly prove sufficient to cause some severe gusts with thunderstorms. LCL heights being low and the abundant opportunity for low-level flow modification by mountains suggest that one or two tornadoes may occur as well. The frontal zone is expected to move slightly eastward during the remainder of the period so that the convective activity is expected to shift slightly eastward. High amounts of precipitation are forecast that may lead to localised flooding. Accumulations of 50 - 100 mm are expected in places.

#