Storm Forecast
Valid: Sat 29 Aug 2015 06:00 to Sun 30 Aug 2015 06:00 UTC
Issued: Fri 28 Aug 2015 22:14
Forecaster: DAFIS

A level 1 was issued for France, Benelux and NW Germany mainly for excessive rain, large hail, severe winds and tornadoes.

A level 1 was issued for parts of Spain and Portugal mainly for large hail and severe wind gusts.

SYNOPSIS

A large scale vortex is situated North from the UK and an extensive frontal zone runs from the Azores islands to Russia. The highlight of this synoptic pattern will be a warm sector of the aforementioned front that will move northwards from Central Europe towards the Benelux area during the second half of the Saturday.
A shortwave trough associated with a cyclonic vortex on the surface, will affect the Iberian Peninsula with some storms that may become severe. In the rest of the continent, high geopotentials and stable conditions prevail except from the NW Russia where some diurnally driven thunderstorms are not forecast to become severe.

DISCUSSION

.... France and Benelux area ....

Warm and moist air masses are moving North from the Central Europe towards the level 1 area and result in high MLCAPE values that are juxtaposed with very strong DLS values up to 35 m/s. Nevertheless, DLS of 20 - 25 m/s overlaps with 1.5 to 2 kJ of MLCAPE and high SREH indicate that any storm in the area from North France all the way to NW Germany will become severe. A linear convective system is expected during the late afternoon and one or two MCCs in Benelux area later in the night. Excessive rainfall is forecast mainly for Belgium, where PW in WRF runs exceeds the 40mm. LCLs below 1000m and signals of LLS in NWP models give a probability of tornado occurrence.

.... Spain and Portugal ....

An embedded shortwave trough associated with a cyclonic vortex on the surface, will affect the Iberian Peninsula with some storms during the afternoon and an organized storm is forecast, according to DLS values of 15 - 20 m/s, especially in western parts of Spain. Diurnal heat results in very steep lapse rates but the BL is not as humid as the coastal areas, so an important role is given to the near surface winds that will transfer humid air masses in the continental parts of the Iberian Peninsula. There are uncertainties about CI but if storms form in the afternoon will result in large hail and severe wind gusts (severe downbursts) due to dry mid - level parts of the troposphere and high LCLs (>1500m).