Storm Forecast
Valid: Wed 28 Mar 2007 11:00 to Thu 29 Mar 2007 06:00 UTC
Issued: Wed 28 Mar 2007 10:25
Forecaster: GATZEN

SYNOPSIS

Blocking high over eastern Europe weakens but remains quasi-stationary. To the west and south, weak low pressure area evades into Mediterranean. Mid-level cold air mass is also present over this region, creating rather steep lapse rates. Given moist low-levels over most of the region, weak instability is epxected and also indicated by latest ascends. On Wednesday, upper low over Italy region moves northward into northern Balkans, where low-level moisture is relatively weak. A few showers and isolated thunderstorms may develop, but given weak vertical wind shear, organized thunderstorms are not expected. Small hail and strong wind gusts due to relatively steep low-level lapse rates are not completely ruled out.

From France to Iberian Peninsula, surface convergence will develop during the period, and geiven mid-level cold air mass and steep lapse rates as well as some moisture flux convergence and rather strong diurnal heating, instability is expected to form. Showers and thunderstorms are forecast to form. Given weak vertical wind shear, convection is forecast to be unorganized and short-lived. Downdraft wind gusts as well as small hail is forecast with the stronger cells.

Over western Mediterranean, upper low and mid-level cold air mass as well as rather rich boundary-layer moisture are present, and latest ascends show weak instability or at least neutral lapse rates. Showers and thunderstorms are forecast to develop. Given weak vertical wind shear, thunderstorms are expected to be unorganized. During the period, a short-wave trough/vort-max migrates north-eastward into southern/central Mediterranean. Quasigeostrophic forcing especially at the eastern flank of the propagating jet streak is expected during the afternoon/evening and night hours. Showers and thunderstorms are forecast to go on during the evening and night and will likely merge into a cluster. Especielly over the southern portions, increasing vertical wind shear due to moderate easterly surface winds and increasing south-westerly winds aloft will be favorable for a few organized cells. Strong vertical wind shear is expected to remain over Africa, though. Current thinking is that widespread convection will form due to quasigeostrophic forcing, and widespread rain with embedded thunderstorms will develop over southern Mediterranean during the night. Tornadoes seem to be not likely, but given rather strong low-level wind shear, one or two events are not completely ruled out