Storm Forecast
Valid: Sat 27 Nov 2010 06:00 to Sun 28 Nov 2010 06:00 UTC
Issued: Sat 27 Nov 2010 02:23
Forecaster: VAN DER VELDE

A level 1 was issued for NW Turkey mainly for excessive convective rain and a tornado chance.
A level 1 was issued for W Greece for a tornado/severe gusts/hail chance.
A level 1 was issued for N Morocco and S Spain for a tornado chance and excessive precipitation.

SYNOPSIS

Cold air dominates Europe as far south as 40-45°N where a frontal boundary with the warmer air resides. The front is under a strong jetstream and warm air will push northward into the Mediterranean later in the forecast period. A large cold upper low is present over western Europe, with several low pressure centers within, mainly near the east coast of England and between England and France. The airmass is unstable with snowshowers and isolated thunder. They tend to cluster more in the coastal convergence zones and vorticity centers.
In the warm airmass southwest of the Iberian peninsula, a low pressure area forms in the frontal region, moving east-northeastwards, and brings unstable warm air onshore.

DISCUSSION

...S Spain, N Morocco...

CAPE of >500 J/kg predicted by GFS and strong vertical windshear (15-20 m/s deep layer shear, 15 m/s low level shear, and up to 300 m²/s² 0-3 km SREH), low cloud base, and synoptic/mesoscale lift can create favorable conditions for mesocyclonic convection capable of producing a tornado. Locally also excessive convective rainfall may occur (but the higher threat is predicted for Monday).

...W Greece...

Similar shear and instability as for the above described area, but stronger mid level/deep layer shear (30 m/s), this small area also has a chance of tornadoes and local large hail. The region has the nicer looking model hodographs (constantly veering winds with height over a deep layer). The strong flow supports also severe convective wind gusts. There is not a clearly defined synoptic forcing mechanism, GFS shows a small local convergence zone.

...NW Turkey, far E Greece and SE Bulgaria...

GFS and ECMWF predict that convective rain will persist in a band through this area for a long time. It can lead to excessive local rain sums. Besides that, wind and shear values are both strong, with SREH possibly above 400 m²/s² and low level shear near 17 m/s can support tornadoes and large hail as well.