Storm Forecast
Valid: Tue 07 Oct 2008 06:00 to Wed 08 Oct 2008 06:00 UTC
Issued: Tue 07 Oct 2008 03:27
Forecaster: VAN DER VELDE
SYNOPSIS
A long ridge of high MSL pressure is stretched out between Italy and the Baltics. East of it, an old low pressure area/cold pool and associated thunderstorms track slowly over Ukraine.
From the west an occlusion in an elongated trough enters western Europe and will reach the Benelux late in the period. A wave develops over the UK. The front has some (elevated) conditionally unstable areas along it, at the time of writing west of Portugal. The Mediterranean coast of France can see some thunderstorms developing as the occlusion and mid level vorticity maximum arrive in the area, late in the period.
DISCUSSION
..Portugal...
As a cold front reaches Portugal in the morning and afternoon, large SREH values of 200-350 m2/s2 are predicted on the warm side, and >10 m/s low level shear. More inland the values are highest, and more coastward the instability should be highest. Supercells can develop in this environment with a potential for an isolated tornado or large hail event. Cells can train along the front and cause flash flooding.
...central UK...
Mid level PV maximum behind the frontal wave and GFS ICAPE and EL suggest elevated or sfc-based thunderstorms can be embedded in the frontal region. At the occlusion point low level shear is predicted to be less than required for tornadoes, but southward values >8 m/s may be present. SREH will be enhanced but generally less than 200 m2/s2.
...Ukraine...
GFS shows strong 0-3 km CAPE values, but 00Z soundings are neutral (but generally low quality sondes). As warm moist air from the Black Sea is advected inland, slow-moving storms can develop with potential of flash floods as the upper low is stagnant and the flow within weak. This is also the typical setting for spouts.
...other...
Marginal instability has been hinted at for SW France, parts of Spain at night, and northern Italy, southern Austria and Hungary. In the latter region 0-3 km CAPE and weak winds could support spouts, but chances seem very marginal.
