Storm Forecast
Valid: Thu 24 May 2012 06:00 to Fri 25 May 2012 06:00 UTC
Issued: Wed 23 May 2012 22:09
Forecaster: GATZEN

A level 1 was issued for the western British Isles, eastern France, the Benelux countries, western and southern Germany, the Alpine region mainly for large hail.

A level 1 was issued for northern Italy, southern Austria, and Slovenia mainly for large hail.

A level 1 was issued from Hungary to the Adriatic Sea mainly for large hail and tornadoes.

A level 1 was issued for Romania, Bulgaria and surroundings mainly for large hail and excessive precipitation.

A level 1 was issued for Turkey mainly for large hail.

SYNOPSIS

The blocking ridge remains across the North Sea. Cold air masses spread south-westward at the flank of this high and will lead to persisting low geopotential across south-eastern Europe. Colder air will also reach the northern Balkans and Germany during the period. Ahead of the cold front, a moist and unstable air mass originating from eastern Europe will affect a region from the western British Isles to the Alpine region and the northern Balkans at Thursday.

DISCUSSION

The western British Isles, France and north-eastern Spain, the Benelux countries, western and southern Germany, the Alpine region

Latest soundings and model data indicate rich boundary-layer moisture over a broad region that is advected southward across France. Lapse rates increasing to the north-east lead to rather strong instability. Across the Benelux countries, up to 2000 J/kg MLCAPE has been observed. An elevated mixed layer will advect westward into northern France and the North Sea and England. Further south, weaker lapse rates are present, but rich low- level moisture will likely lead to CAPE during the day as well. Given a weakly-forced situation, low-level forcing like sea-breeze fronts and upslope flow will be the main sources of lift/initiation. Storms will spread along these features as well as along outflow-boundaries until the late evening hours, when storms will decay. Although the vertical wind shear is weak, pulse storms will be capable of producing large hail locally as well as excessive precipitation, especially in the northern portions. Briefly severe wind gusts are not ruled out.

Northern Balkans and surroundings, northern Italy

Rich low-level moisture will be present ahead of the surface cold front, while colder mid-level air advects southward rather quickly. Embedded short-wave troughs and increasing northerly mid-level winds will affect eastern central Europe and the northern Balkans at Thursday. Some QG lift will enhance the potential of thunderstorms in an unstable air mass characterized by steep mid-level lapse rates and rich boundary-layer moisture. While the instability decreases from west to east, vertical wind shear will increase slightly. Multicells are expected that may produce large hail locally. Severe wind gusts are not ruled out with the stronger storms. Increasing low-level vertical wind shear in the evening hours is suggested to increase the potential of supercells and tornadoes especially from the Slovakian region to the Adriatic. Further east, weak mid-level winds across Romania will lead to slow moving storms capable of producing locally excessive precipitation.

Dry air masses spreading into the region from the north will lead to decaying storms from Poland into the northern Balkans during the period. Storms across the central Balkans may go on until the morning hours.

Turkey

A strong mid-level jet affects Turkey ahead of the south-east-European trough. Rather strong vertical wind shear up to 20 m/s 0-6 km bulk shear and QG forcing are forecast. Steep lapse rates are present and low-level moisture is expected to increase from the north during the day. Thunderstorms are expected that may organize into multicells or supercells, capable of producing large hail. Severe wind gusts are not ruled out. Convective activity will decrease in the evening hours, but some storms may go on during the night hours.