Storm Forecast
Valid: Thu 03 Mar 2011 06:00 to Fri 04 Mar 2011 06:00 UTC
Issued: Wed 02 Mar 2011 17:40
Forecaster: GATZEN

SYNOPSIS

A deep polar trough is located across southern Europe leading to a strong south-westerly mid-level flow across the central Mediterranean Sea. At low levels, easterly winds advect moist air masses into the central Mediterranean ahead of a low pressure system over the Atlas mountains. Mostly stable air masses dominate most of Europe.

DISCUSSION

West Mediterranean to Adriatic Sea

A broad trough that is placed over the west Mediterranean is filled with cold polar air masses with mid-level temperatures below -28°C. Low-level heating over the Mediterranean Sea as well as over the larger islands is expected to lead to steep low-level lapse rates.

Given rather steep lapse rates close to the moist adiabate at mid-levels, a rather cold equilibrium level temperature is possible as indicated by latest soundings. Latest observations also indicate scattered thunderstorms.

On Thursday, convective activity is forecast to go on over the Mediterranean Sea. Given the rather weak low-level moisture and weak vertical wind shear, severe thunderstorms are not forecast. A few waterspouts are not ruled out especially near the coasts of the Adriatic Sea.

Over the larger islands and southern Italy, daytime heating is forecast to be strong enough for initiation, and additional thunderstorms are forecast to develop during the day. These storms are also expected to be unorganized, but locally small hail and strong wind gusts are expected before the storms decay in the evening hours.

Central Mediterranean

The center of low surface pressure is forecast to be located over northern Africa. This is associated with easterly surface winds over the southern/central Mediterranean and a frontal boundary at the eastern flank of the surface low is forecast to move westward again. This warm front will also be associated with low-level moisture advection into the central Mediterranean.

Warm air advection atop of the boundary-layer as well as weak synoptic forcing at the anticyclonically sheared exit of the mid-level jet stream will likely limit the chance of initiation. However, a rather well-defined surface front/convergence is indicated by latest models, and current thinking is that stratiform precipitation will likely develop.

Late in the period, the mid-level jet spreads eastward, leading to more forcing and steepening lapse rates. Elevated convection is forecast that will likely be imbedded in the stratiform precipitation area. Storms are not expected to root to the boundary-layer where they would profit from the moderately-sheared environment near the warm front and severe storms are not forecast.