Storm Forecast
Valid: Tue 20 Mar 2007 06:00 to Wed 21 Mar 2007 06:00 UTC
Issued: Tue 20 Mar 2007 02:53
Forecaster: VAN DER VELDE

SYNOPSIS

A large amplitude, long wave upper trough filled with very cold air has settled over Europe. Cold air with wintery thundershowers is advected south and eastward, as far as the African coast and the cold front over southern Italy into the Balkan.
Ahead of the cold front, GFS indicates possibilities for deep convection in the much warmer airmass streaming up into Albania and western Greece.


DISCUSSION

...extreme southeastern Italy, Albania, western Greece...

A tongue of higher theta-e and very strong low level convergence and MLCAPE >250 J/kg in GFS creates a setup favourable for widespread or violent severe weather events in this area. 00Z Brindisi (45 kts at 925 hPa) and Trapani seem to confirm instability and strongly veering winds with height in the warm sector. GFS calculates deep layer shear >25 m/s, low level shear of >10 m/s and 0-3 km SREH >250 m2/s2 overlaying the area with CAPE between 12Z-18Z.
Given strong forcing due to warm air advection, arrival of a mid level vorticity maximum, and frontal convergence, thinking is that one or several MCSes may form with a chance of severe convective gusts, but supercells with a chance of tornadoes and large hail appear quite possible. Local flash flooding may occur as well.


...northern Spain...

A continuation of the previous day with little change. Instability should slowly decrease, but expect a few hundred J/kg to remain possible. Deep layer shear and low-level shear (over land) are sufficient to sustain a small tornado chance with any storms that manage to develop a mesocyclone.

...northern Algeria and Tunesia...

With the jetstream overhead and a pool of unstable air advecting onshore, waterspouts and tornadoes are possible. GFS indicates only low storm tops and subsidence, but given solid 0-3 km CAPE, >10 m/s low level shear and very strong >40 m/s deep layer shear, a risk for isolated severe weather seems warranted.

...southwestern Turkey...

During the morning hours, instability is present in a zone of highly veering winds with height and moderate deep layer shear, and low level convergence. Storms may develop long-lived or rotating characteristics with a chance of large hail. Instability seems to become suppressed a bit and sliding eastward during the day.