Storm Forecast
Valid: Thu 26 Oct 2006 06:00 to Fri 27 Oct 2006 06:00 UTC
Issued: Wed 25 Oct 2006 19:13
Forecaster: GATZEN

SYNOPSIS

Western European trough cuts off SE of Iberian Peninsula. Northern trough axis accelerates eastward reaching Denmark during the night. To the south ... high over Mediterranean ridges into south-eastern Europe. At lower levels ... unseasonably warm subtropic air mass spreads into France, Alpine region, and Germany ahead of a cold front over southern North Sea and western France. Unstable maritime air mass remains W of Iberian Peninsula.

DISCUSSION

France

Strong southerly flow is present over France ... reaching around 20 m/s at the 850 hPa level during the period. Warm air mass spreads northward that is characterized by relatively steep mid-level lapse rates as indicated by latest soundings. A strong south-easterly LLJ is forecast to develop over southern France during the day ... advecting moist and warm boundary-layer air mass into central France. During the day ... a cold front moves into western France ... and low-level convergence is expected over central France. ATTM ... it is not clear that instability will realize. Latest models indicate at least some surface-based CAPE during the day ... as well as elevated CAPE ... and given low-level convergence ... formation of showers and isolated thunderstorms is not ruled out. As vertical wind shear will be strong ... convective cells will likely organize ... and given strong veering over central France ... a few mesocyclones are not ruled out ... capable of producing isolated hail/strong wind gusts. Limiting factor will be rather cool boundary-layer/weak insolation as well as rather weak QG forcing in the range of the cut-off process. Showers and thunderstorms that form will gradually weaken during the night ... moving north-eastward into western Germany.

South-western Iberian Peninsula

Unstable maritime air mass remains over south-western Iberian Peninsula ... and models agree that convective activity goes on. While upper cut-off migrates southward ... vertical wind shear is expected to weaken ... and severe convection is rather unlikely. Given moist and unstable low-level air mass ... as well as locally strong LLS near the coasts ... marginally chance for tornadoes is not ruled out.