Storm Forecast
Valid: Mon 29 Nov 2010 06:00 to Tue 30 Nov 2010 06:00 UTC
Issued: Mon 29 Nov 2010 04:22
Forecaster: DAHL

A level 1 was issued across the southwestern and southeastern Balkan States as well as the northern Aegean Regions into the western Black Sea mainly for severe wind gusts and Tornadoes.

A level 1 was issued across the Iberian west coast mainly for tornadoes and severe wind gusts.

... SYNOPSIS ...

A large, positively tilted, quasi-stationary upper longwave trough is anchored over the northwestern parts of Europe, yielding an intense and deep southwesterly flow along the frontal zone over the Mediterranean. Jet streaks are present amidst this frontal zone and maintain the SFC low analyzed over central Italy on Sunday evening, and an upstream frontal wave that should cross the western and central Mediterranean on Monday.

... DISCUSSION ...

... Balkan States into Black-Sea Region ...

Unseasonably steep mid-level lapse rates were observed over the central Mediterranean on Sunday, which should linger over the Aegean regions and the western Black Sea until Monday evening. Along with boundary-layer mixing ratios of between 8 and 10 g/kg, MLCAPEs in the 500 to 1000 J/kg should result over the Aegean ... probably somewhat less farther north.

Deep-layer shear magnitude is simulated to locally exceed 30 m/s, with 0-1 km shear in excess of 15 m/s. This is well above the thresholds for tornadic supercells.

However, it seems that in the nearby upper vorticity maximum will be too far north, so that the cap/forcing combination will not be supportive of widespread convective development where thermodynamic profiles will be best (WRF12km does not simulate any precipitation over the northern Aegean).

Altogether ... although the thermodynamic fields should be rather weak across most of the LVL1 area, the strong shear should support a couple of tornadoes and severe wind gusts where convection forms.

Cellular polar-air convection should persist over the Gulf of Biscay and off the Iberian Atlantic west coast. Some of the convection may spead into western Iberia late in the period, but should not persist as it makes landfall. Still, quite strong shear will exist, so that especially in the coastal regions of Portugal, a brief tornado or two and/or severe straight-line winds cannot be discounted. A level 1 threat seems marginally warranted.