Storm Forecast
Valid: Thu 25 Feb 2010 06:00 to Fri 26 Feb 2010 06:00 UTC
Issued: Wed 24 Feb 2010 15:05
Forecaster: GATZEN

A level 1 was issued for the Bay of Biscay and western France mainly for severe wind gusts.

SYNOPSIS

Weak geopotential extends over Europe downstream of a strong mid-level jet that spreads into western Europe during the period. This will be associated with a short-wave trough actually over France that is pushed across Central Europe and a following intense short-wave trough that will travel across the Bay of Biscay and France. Increasing warm air advection is forecast across western and south-western Europe.

DISCUSSION

Bay of Biscay region

While the strong mid-level jet streak enters western Europe, an intense surface low pressure systems will move into the northern Bay of Biscay. In the range of strong QG forcing due to a coupled jet, this low will further deepen while the warm front will move into western France. To the north-west of the mid-level jet, the forcing will be likely strong enough to produce neutral to slightly unstable lapse rates in the warm air mass. Rather deep instability may be also favoured as dry air masses in the range of a dry intrusion may cool rather rapidly as indicated by latest GFS model run.

Main focus of deep convection will be the cold front or cold front occlusion that travels across the Bay of Biscay and north-western France during the day. Strong forced ascend along the cold front will likely lead to a narrow line of convection that will become deeper in the range of the cyclonic flank of the mid-level jet streak. At least some lightning is expected in the range of this line. Along of the leading gust front, severe wind gusts are not ruled out given the strong low-level winds of about 25 m/s at the 850 hPa level and the high speed of the gust front. A well-developed MCS is not expected to be likely as the warm sector will be quite small and the amount of instability will remain poor. Later in the period, low levels will likely stabilize as the cold front undercuts the warm sector over northern France.

In the afternoon hours, another region of instability is expected across the Bay of Biscay ahead of the trough axis, where strong QG forcing will likely result in weak instability indicated by the forecast of rather cold mid levels. Showers and thunderstorms are forecast that will travel rapidly into western France. Given increasing low-level winds of up to 30 m/s at the 850 hPa level, severe wind gusts are forecast with the stronger storms.

Upstream of this trough, a strong sting jet will likely pose a significant wind threat that will be not related significantly to convection.