Storm Forecast
Valid: Thu 26 Jul 2012 06:00 to Fri 27 Jul 2012 06:00 UTC
Issued: Thu 26 Jul 2012 06:24
Forecaster: GATZEN

A level 1 was issued for Poland, Czech Republic, Slovakia, south-eastern Germany, Austria, Hungary, northern and central Balkans mainly for excessive precipitation and tornadoes.

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

A level 1 was issued for northern Spain and surroundings mainly or large or very large hail.

SYNOPSIS

A mid-level trough over east central Europe is weakening and slowly moves eastward while a ridge spreads into central Europe from the west. A deep Atlantic trough affects the Iberian Peninsula. To the north, an intense trough starts to amplify over the British Isles.

DISCUSSION

Poland, Czech Republic, Slovakia, south-eastern Germany, Austria, Hungary, northern and central Balkans

In the range of the broad mid-level trough, a convectively mixed air mass with rich moisture is indicated by latest soundings. Weak to moderate instability is expected over most places reaching more than 1000 J/kg locally. Slow-moving thunderstorms are expected. Excessive precipitation is quite likely given the high water content and slow storm motion. Additionally, the weak wind field and stron low-level buoyancy will again be supportive for spout-type tornadoes. Large hail and severe wind gusts are not ruled out with stronger pulse storms.

Western Romania, western Bulgaria, and surroundings

At the eastern flank of the mid-level trough, a frontal boundary extends across this region. A parallel-stratiform MCS has developed over western Romania overnight and will go on during the morning, capable of producing heavy rain. In he wake of this convection, diurnal heating will lead to substantial CAPE. New thunderstorms are expected along the frontal boundary that move northwards with the mean wind. Given northerly low-level winds, enhanced 0-3 km vertical wind shear will be supportive for organzied convection. Supercells may develop, capable of producing large hail. Excessive precipitatin and a tornado are not ruled out. Convection may go on well into the night given ongoing forcing along the frontal boundary due to warm air advection.

Iberian Peninsula

Ahead of the Atlantic trough, southerly winds will intensify today. Given a strong capping inversion spreading into Iberia, convective activity seem to be most likely over the northern portions, where rather rich low-level moisture is indicated by latest soundings. Diurnal heating will again lead to rather strong instability and a thermal low over Spain, associated with easterly winds over northern Spain. About 10 m/s 0-3 km bulk shear is expected and supercells are forecast that may produce large or very large hail. Further south, additional storms are expected due to the strong diurnal heating. With weaker wind shear, severe potential is lower, but stronger storms may produce large hail and strong to severe wind gusts. Over eastern Spain, strong vertical wind shear will be in place, but a strong capping inversion is expeced to suppress deep moist convection.

Western France, central British Isles

Latest soundings indicate rather stable conditions over western Europe. Low-level moisture has started to increase from the east and will lilely further increase along convergence lines. In the aftenoon and evening, the approaching mid-level trough will lead to some QG forcing and the capping inversion is expected to become weaker. Thunderstoms seem to be likely across northern England and across western France. With moderate mid-level shear, these storms may organize into multicells and a marginal hail risk is expeced. Later in the period, convection may go on across western France where an MCS may develop. Large hail and excessive rain are not ruled out, but the threat seems to be too marginal for a level 1.

Eastern France to eastern Germany, Alps

Weak winds and moderate instability are expected today. Thunderstorms that initiate over the mountains will have a potential to produce excessive precipitation due to slow storm motion and backbuilding from the north and east. Low storm coverage is expected and a level 1 is not issued.