Storm Forecast
Valid: Sun 01 Aug 2010 06:00 to Mon 02 Aug 2010 06:00 UTC
Issued: Sun 01 Aug 2010 05:17
Forecaster: SCHLENCZEK
A level 1 was issued for NE Spain, most parts of France and extreme SW Germany for large hail, severe wind gusts and excessive rainfall.
A level 1 was issued for E Romania, W Ukraine and S Belarus for large hail, severe wind gusts and excessive rainfall.
SYNOPSIS
The 300 hPa geopotential / temperature map shows a stationary low pressure system over the northern North Sea and four shortwave troughs in its vicinity. The shortwave over SW England should move across France and western Germany during the period while merging with the shortwave trough over northern Iberia, leading to some QG forcing ahead of the cold front which stretches from the Bay of Biscay via NW Germany towards southern Sweden. Along this cold front, some hundred J/kg CAPE should become available during the afternoon and thunderstorms will likely develop in a strongly sheared environment. Another shortwave trough is initially located over southern Norway and will move to the north while weakening. The most important upper level feature on Sunday is an upper trough over the Balkans which is expected to shift eastwards while developing some shortwaves further upstream. This feature is located close to a stationary frontal boundary over SE Europe which separates moderately warm air over south-central Europe from very hot subtropical air over eastern Europe. Instability should be rather modest with 2m temperatures in the upper thirties and dewpoints in the upper tens / lower twenties.
DISCUSSION
...Northern Iberia and south-central France...
Around 800 - 1200 J/kg CAPE are expected over N Iberia and C France into SW Germany in the afternoon and evening hours ahead of an upper vort-max in the vicinity of a 30 m/s upper jet streak. The 0-6 km shear vector with 20 - 25 m/s magnitude and the frontal boundary will be almost parallel and therefore isolated organized multicells and supercells will likely merge into a linear MCS which will move across France and parts of SW / W Germany. In the initial stage of the convective development, large hail should be the primary threat. Later on, severe wind gusts and local excessive rainfall are expected to become more important. Storms should be rather high-based which lowers the chance of a tornado but an isolated event is not ruled out, though.
...Eastern France and southwestern Germany...
Some hundred J/kg CAPE are forecast in an environment with 10 - 15 m/s deep layer shear, locally up to 20 m/s. Some storms are recently developing over Germany and it is expected that remnants of these storms will hinder insolation during the morning / afternoon hours. Even though storms tend to stay rather discrete now, it is probable that some clusters will develop during the period with isolated large hail and locally excessive rainfall.
...Eastern Romania, west-central Ukraine, southern Belarus...
A plume of moist and hot air that originates from the Bosporus region is advected northwards into Romania and should reach Ukraine and Belarus in the evening / night hours. QG forcing is quite weak in this region but the cold front itself should provide enough lift for initiation. Locally, MLCAPE in order of more than 1000 J/kg should be expected in an environment with 10 - 15 m/s deep layer shear and locally 150 - 200 mē/sē SRH3. In the initial stage, organized multicells and supercells may produce large hail and severe wind gusts. The front-normal component of the storm-relative upper flow is very small and storms may tend to cluster into one or two MCSs which should move northwards. In the southern parts of the level 1 area, severe wind gusts should be the primary threat from the MCSs whereas excessive rainfall should become more important in the northern parts as storms tend to slow down when moving northwards into a region with decreasing upper level winds.
