Storm Forecast
Valid: Sun 17 Mar 2013 06:00 to Mon 18 Mar 2013 06:00 UTC
Issued: Sun 17 Mar 2013 05:41
Forecaster: VAN DER VELDE
A level 1 was issued for northwestern France mainly for some chance of tornadoes.
A level 1 was issued for southern Spain and northern Morocco mainly for isolated large hail and severe wind gusts.
SYNOPSIS
A large low pressure system is situated over British Isles and its radius of influence spans entire western Europe. The low is rather old and its frontal systems broken up, the more active systems are two shortwave troughs moving around Ireland into the English Channel. The temperature gradient increases over the Iberian Peninsula as result of cold air advection from the large low towards the south and warm air advection from the subtropics. As slight frontal wave develops and the warm sector is unstably stratified.
An upper cold pool resides east of Poland, cut off from any warm air by the Russian cold airmass.
DISCUSSION
...northwestern France area...
In several models, the better CAPE seems to lie north of the jet, but an overlap between more than 20 m/s DLS and CAPE should be present in the southern half of this level 1 area. The northern half, however, still shows more than 10 m/s bulk shear in the 0-1 km layer, which combined with low LCL heights may favor a tornado if a mesocyclone-bearing storm could form (probably needs the deep shear). Hodographs show modest curvature and helicity, though.
...southern Iberia, northern Morocco...
Most CAPE comes in from the west during the morning while the better deep layer shear shifts eastward ahead of it, so there is not an ideal overlap, only in a narrow region. The stronger 0-1 km shear will probably not be useful without sufficient kinematics in the 1-6 km layer. However, at time of writing some active storms obviously are developing ahead of this predicted CAPE maximum around Gibraltar, perhaps elevated, and should be in a fast flow with decent effective deep layer shear. Hence an isolated wind gusts and/or a large hail event is possible.
