Storm Forecast
Valid: Sat 02 Apr 2011 06:00 to Sun 03 Apr 2011 06:00 UTC
Issued: Sat 02 Apr 2011 02:47
Forecaster: VAN DER VELDE
A level 1 was issued for southern Turkey and Cyprus for tornadoes and severe wind gusts.
A level 1 was issued for the western Iberian peninsula and Basque region mainly for marginally large hail.
SYNOPSIS
A mildly unstable summer-like warm plume situation is developing over western Europe. Meanwhile, a large low with unstable airmass following behind a cold front, where CAPE and shear overlap, passes over Turkey.
DISCUSSION
...Turkey and Cyprus...
A cold front backed by a good PV anomaly passes over southern Turkey and Cyprus and features a few hundred J/kg MLCAPE, while a jet ensures more than 25 m/s deep layer shear (0-6 km). Low level shear is also more than 10 m/s/km but seems displaced ahead of the front. GFS indicates a capped environment except a little land-inwards over Turkey. There the chances of a tornado or severe gusts are sufficiently enhanced for a level 1.
...Portugal/Spain and France...
While very dry air in all levels currently resides over these areas, GFS and ECMWF advect moist air from the Atlantic into the region, already visible in the 00Z La Coruna sounding. Additional destabilization from insolation, small predicted LFC-LCL differences (weak cap) and a developing PV maximum over Portugal suggests the convective precip signals in both models have sufficient support. Deep level shear and storm-relative helicity reach somewhat elevated values (>20 m/s 0-6 km shear, >200 mē/sē SREH 0-3 km) which would qualify for level 1 for large hail over Portugal and Spain, however, the modest MLCAPE and low equilibrium levels combined with a strongly sheared environment could rather cause storms struggling to develop into something strong. Since CAPE is stronger and in a small region sufficiently uncapped over N Spain/SW France, with somewhat higher SREH values also, more potential exists there for an isolated storm producing large hail.
During the night both GFS and ECMWF develop lots of convective precipitation over France, associated with CAPE from a shallow layer of elevated parcels.As QG lift sources seem to lag this precipitation area, and instability and EL heights aren't that enhanced, thunder percentages have been kept low. Also the afternoon convective chances in central France depend critically on actual moisture content and upper destabilization.
