Storm Forecast
Valid: Wed 05 Aug 2009 06:00 to Thu 06 Aug 2009 06:00 UTC
Issued: Wed 05 Aug 2009 04:59
Forecaster: SCHLENCZEK

A level 1 was issued for N Greece, FYR Macedonia, Serbia, W Bulgaria and W Romania mainly for excessive precipitation, large hail and severe gusts.

A level 1 was issued for E Hungary, E Slovak Rep, SE Poland and SW Ukraine mainly for excessive precipitation

SYNOPSIS

The upper low over the N Balkans moves southeastward towards W Turkey during the period. Ahead of this low, advection of hot and moist air over parts of Greece and Bulgaria will continue. A northwesterly 30 m/s jet streak at 300 hPa over C Italy / N Adriatic translates southeastward towards S Greece with its left exit region over C Greece. In the wake of the trough, moderately warm and unstable air is present over large portions of E / SE Europe. Most of the thunderstorms on Wednesday will occur in this region.

Ahead of an upper trough centered over the NE Atlantic, advection of warm and moist air in a strong SWerly flow continues over parts of Spain and S France. The airmass over Spain will remain strongly capped even though LL moisture will slightly increase during the day. Isolated thunderstorms may occur over N Spain / extreme S France in the evening hours.

Some showers and thunderstorms are also possible over NW France and the southeastern parts of England near the cold front of the Atlantic low pressure complex. Deep layer shear should be in order of 20 m/s but there are hardly a few hundred J/kg CAPE.

DISCUSSION

...N Spain, extreme S France...

Recent runs of GFS assume that the strong cap with about -200 J/kg CIN will remain over this region but isolated thunderstorms are possible in the mountains. There should be about 1 kJ/kg MLCAPE and 10 - 15 m/s deep layer shear. If storms develop, they should be capable of producing strong to severe gusts and perhaps some marginally severe hail. Right now, the expected storm coverage is too low for a level 1 but an update may become necessary later on.

...Balkans, W Bulgaria, W Romania...

Compared to the situation on Tuesday, deep layer shear has decreased to about 10 - 15 m/s in most places. This environment with 1 - 1,5 kJ/kg MLCAPE will be favourable for multicells / multicell clusters which move very slowly and lead to excessive rainfall and flooding. There should also be a slight chance of isolated large hail and severe gusts but heavy rain should be the main threat. Thunderstorm activity will continue into the late evening / night hours.

...E Hungary, E Slovak Rep, SW Ukraine, SE Poland...

In parts of Hungary, Slovak. Rep. and Poland / W Ukraine there should be some 500 - 1000 J/kg CAPE in a weakly sheared environment. If storms manage to persist over the same region for several hours, torrential rainfall may lead to local flooding. Right now, there are lots of mid level clouds that may hinder insolation but a level 1 threat should be marginally warranted.