Storm Forecast
Valid: Thu 10 Oct 2013 06:00 to Fri 11 Oct 2013 06:00 UTC
Issued: Wed 09 Oct 2013 22:39
Forecaster: GATZEN

A level 2 was issued for western Albania and surroundings mainly for excessive precipitation.

A level 1 was issued for northern Algeria and Tunisia mainly for large hail and severe wind gusts.

A level 1 was issued for the central Mediterranean from Tunisia across southern Italy to the southern Adriatic and Greece mainly for excessive precipitation and tornadoes and to a lower extend large hail and severe wind gusts.

A level 1 was issued for the northern Adriatic and surroundings mainly for excessive precipitation, large hail, severe wind gusts, and tornadoes.

SYNOPSIS

An intense cut-off process is underway at the eastern flank of an Atlantic ridge. At the end of the forecast period, a closed low will be centred across France. This will be associated with a westerly to south-westerly flow across the Mediterranean and warm air advection especially in the eastern portions. Across eastern Europe, a weak trough will move north-eastward.

DISCUSSION

Algeria to Sicily and Greece

Increasing warm air advection is expected across the area due to south-westerly flow in the wake of a lifting trough moving north-east into eastern Europe. An elevated mixed layer will spread north-east across the south Mediterranean Sea. The low-level mixing ratio will increase in the capped maritime boundary-layer due to the warm sea surface temperature. The plume of rich boundary-layer moisture will advect northward with the low-level flow, leaving the area of the strong inversion.

Additionally, several jet streaks will travel east along the 20 m/s jet stream that will provide QG lift from Algeria towards Greece.

Current thinking is that another round of frequent convective activity will affect the area until Friday morning. Storms will likely organize given the strong deep layer vertical wind shear, and mesoscale convective systems may move east or northeast.

The main threat will be excessive rain through-out the period as the storms will affect the same area along the warm air advection regime from Sicily to Greece for a longer time. Additionally, the high moisture will increase the chance of intense downdrafts. The western coasts and mountain areas are most at risk due to upslope flow where a level 2 was issued.

An additional risk are tornadoes due to locally large low-level hodographs together with strong low-level buoyancy near the coasts. Isolated severe wind gusts and large hail are mostly expected across Algeria and Tunisia during the afternoon and evening hours.

Northern Adriatic and surroundings

Strong QG lift is expected ahead of the European cut-off low that will spread into the northern Adriatic late in the period. Given the rather most and warm boundary-layer ahead of the cold front, CAPE is forecast and thunderstorms will likely form especially in the evening and night hours. As vertical wind shear will be strong, storm will quickly organize and supercells and multicells capable of producing large hail and severe wind gusts are forecast. Additionally, excessive precipitation is expected especially in the eastern portions of the area. Near the Adriatic Sea, tornadoes may also occur given the strong low-level vertical wind shear.