Storm Forecast
Valid: Thu 25 Jun 2009 06:00 to Fri 26 Jun 2009 06:00 UTC
Issued: Thu 25 Jun 2009 09:59
Forecaster: GATZEN

A level 1 was issued for portions of Poland mainly for excessive rain.

A level 1 was issued for central Romania to western Ukraine mainly for large hail and severe wind gusts.

A level 1 was issued for eastern Iberia mainly for large hail and severe wind gusts.

A level 1 was issued for south-western Turkey mainly for large hail and severe wind gusts.

SYNOPSIS

Northern Europe is dominated by high pressure centered over Scandinavia. Short-wave troughs do affect northern Scandinavia and northern Russia at the north-eastern flank of this high. To the south, low geopotential located over the northern Atlantic stretches into central Europe and the Balkans, associated with rather strong westerly mid-level winds across the Mediterranean. Ahead of the main trough axis, this mid-level jet curves northward into the western Black Sea region and Ukraine. At lower levels, moderately warm air masses are present over most of Europe, while hot air masses spread northward over the Black Sea region. While poor lapse rates are present in the range of the high over Scandinavia as well as over the east Mediterranean in the range of low-level cold air advection, lapse rates are rather steep. Rich low-level moisture is forecast to build from western Russia to Poland, portions of the Balkans, south-western Mediterranean, and western Europe.

DISCUSSION

Western Russia to Poland and northern Balkans

Hot air masses spread northward across eastern Europe. To the north, a humid low-level air mass is present in the range of a weak west-east orientated mid-level trough axis. QG forcing and low-level convergence is forecast through-out the period. As steep mid-level lapse rates will likely overspread the low-level moist air mass, diurnal heating will result in CAPE around 1000 J/kg.

As vertical wind shear will be weak over most places, severe potential is expected to be quite low. Stronger storms may produce locally severe hail and flash flooding. Strong wind gusts may occur at the southern flank of the convective region, where drier warm air masses spread northward and downdraft CAPE is forecast to be higher. Over Poland, chance for extensive rain my increase in the evening due to weakening winds and associated slow-moving storms, and level 1 is issued.

Central Romania to western Ukraine

A southerly jet affects this region where vertical wind shear is forecast to range around 20 m/s in the lowest 6 km. Thundestorms have already developed in the warm air advection regime. Limiting factor is decreasing QG forcing at the right exit of the mid-level jet. Expect that convective activity will go on in the afternoon hours, but storms may be moe isolated and capable of producing large hail. Severe wind gusts and tornadoes are also forecast given rather strong low-level winds during the day, exceeding 20 m/s at th 700 hPa level. Rather good buoyancy at low levels also indicates a chance of tornadoes with stronger cells. Expected weak coverage is the main reason against a level 2.

North-eastern Iberia

Low-level easterly upslope flow is expected across eastern Iberia, and a convergence zone is expected where low-level moisture flux convergence will likely take place. An EML is expected to spread eastward from the Iberian altiplano and CAPE in the order of 1500 J/kg is forecast. Thunderstorms are forecast to develop during the afternoon hours. Potential of severe weather increases to the south where deep layer vertical wind shear is stronger at the cyclonic flank of the upper westerly jet. Severe wind gusts and large hail is forecast. Limiting factor is rather dry low-level air mass over most places and associated strong capping inversion. To the north, CIN will be weaker, but weak vertical wind shear will limit severe potential.

South-western Turkey

Thunderstorms will likely develop in response to diurnal heating and upslope flow over souther-western Turkey. Given 20 m/s deep layer vertical wind shaer in the range of the southerly jet, stronger storms will be capable of producing large hail. Severe wind gusts are also forecast given well-mixed and dry low-level air mass.

Northern Algeria

Isolated storms that are expected to develop over the Atlas mountains have a potential of producing large hail given strong deep laye vertical wind shear.