Storm Forecast
Valid: Tue 10 Feb 2009 06:00 to Wed 11 Feb 2009 06:00 UTC
Issued: Tue 10 Feb 2009 04:56
Forecaster: VAN DER VELDE

SYNOPSIS

An intense and potential life threatening extratropical storm affects northern France, Benelux and Germany during this forecast period with damaging wind gusts of 90-130 km/h that would suffice for a threat level 2, if produced by convective storms.
However, the chance of long-lived/organized storms is low within the strongest wind field, and no ESTOFEX convective threat level is applicable. Please refer to your national meteorological service for more detailed information about the situation.

GFS predicts the depression to reach its lowest pressure over western Belgium/Netherlands (<976 hPa) around 06Z, after which it slowly moves eastward. The strongest wind field is forecast initially for the northern half of France, shifting to Switzerland and southern Germany during the morning.

The depression opens the gate to unstable maritime arctic air mass rushing southward into Europe. T500 will drop below -35°C and invades British Isles, Benelux, France and the northern Mediterranean by the end of the period.


DISCUSSION

...Belgium, Netherlands, northern Germany...

Near the core of the low over Netherlands and NW Germany, some slight CAPE is produced in the model, but the kinematic situation lacks deep shear and showers remain almost stationary, in contrast to the brief fast-moving cells over Belgium in strong shear at the time of writing. This activity should disappear as BL mixing ratio is predicted to decrease by 2 g/kg.
Some elevated CAPE is predicted for northeastern Germany around 12Z, in a frontal zone with high sr-helicity, but it is not likely to yield convection.

...SW France, Basque region...

Weakly electrified showers will initially occur in strong low level shear and deep layer shear, but the strength decreases as convection becomes more active, and SREH is calculated to be zero, dynamics not very significant. No threat is expected other than an episode of intense snowfall in the Pyrenees, mainly 12Z-03Z.

...NE Italy, Slovenia, Croatia...

As the cold front of the big low passes the Alps, an area of CAPE is supported by GFS but not by Lamma-WRF, although that model does have a precipitation maximum in this area. Given >300 m²/s² SREH3, >20 m/s 0-6 km shear and >12 m/s low level shear, it cannot be ruled out that a tornado would occur. The zone shifts southward with the front during the evening with shear weakening. It supports backbuilding storms but seems not persistent enough to cause flash floods.