Storm Forecast
Valid: Thu 23 Jul 2015 06:00 to Fri 24 Jul 2015 06:00 UTC
Issued: Wed 22 Jul 2015 23:27
Forecaster: GATZEN

A level 1 was issued fort he Baltic States into western Russia mainly for excessive precipitation.

A level 1 was issued for Belarus into the western Ukraine and south-eastern Poland/eastern Czech Republic and Slovakia mainly for large hail.

A level 1 was issued for eastern Spain mainly for large hail.

A level 1 was issued for Sardegna, Corsica, central/southern Italy, and western Balkans mainly for large hail.


SYNOPSIS

A zonal west-southwesterly flow continues across northern Europe during the period. A short-wave trough travels eastward across the southern Baltic Sea and the Baltic States into Russia. At lower levels, a frontal wave affects Poland, Belarus, and the Baltic States. In the wake of the wave, a cold front will extend south-west towards the northern Alps, west Mediterranean, and the Pyrenees. Weak flow is expected across southern Europe.

DISCUSSION

Eastern Poland and Baltic States into Belarus, western Russia, western Ukraine, eastern Czech Republic, and Slovakia

Cool and dry low-level air masses are present across the Baltic States. Warm air advection has set in across Poland and will continue during the night hours. Upstream, a thunderstorm cluster has formed over eastern Germany that spreads into western Poland. Latest models indicate that this cluster will continue given the strong warm air advection and also DCVA. In the morning, elevated storms are therefore expected to enter north-eastern Poland and the southern Baltic States. Chances of severe storms are limited given the cool and stable boundary layer, but excessive rain is possible. If diurnal heating is greater than expected, and surface-based storms form over northern Poland and the Baltic States, very strong low-level vertical wind shear (20 m/s 0-3 km bulk shear) would be available, allowing for supercells capable of producing tornadoes.

During the day, weakening storms are forecast to move across Belarus into western Russia. Best chances for new initiation are expected to the south-west of the first cluster from western/southern Belarus into southern Poland/eastern Czech Republic. Although vertical wind shear will be not too strong, with about 10 to 15 m/s in the lowest 3 km, severe storms are expected given an increasingly moist low-level air mass and CAPE values of 1000 J/kg. Multicells seem to be the dominant storm mode, capable of producing large hail. Severe wind gusts and excessive rain are not ruled out. Storms are forecast to weaken after sunset due to low-level stabilization and weakening QG support in the wake of the short-wave trough.

Alpine region

A cold front will enter the Alps in the morning hours. Given ample low-level moisture and upslope flow, showers and thunderstorms are forecast along this front. Weak lapse rates will limit the overall potential for severe storms, though. Locally, excessive precipitation is forecast. Especially in the southern and eastern parts of the Alps, large hail is not ruled out. Storms will rapidly decay after sunset given weak QG support and low-level cooling.

Eastern Spain

Rather moist low-level air has been advected into eastern Spain. It overlaps with steep lapse rates, allowing for CAPE in the order of 1000 to 2000 J/kg. New storms are forecast on Thursday, initiating over the mountains due to upslope flow. With weak westerly winds above the boundary layer and easterly sea breeze, 0-3 km vertical wind shear can increase in the evening hours to about 10 m/s. This may allow for multicells or supercells, capable of producing large hail. Storms are expected to weaken in the night hours, but some QG lift may support storms especially in the northern portions through-out the night.

Mediterranean and Balkans

In the vicinity of an ill-defined cut-off low, another round of diurnally-driven storms is forecast. Weak vertical wind shear is present, but pulse storms may be capable of producing locally large hail, severe wind gusts, and excessive precipitation.