Storm Forecast
Valid: Thu 04 Jun 2009 06:00 to Fri 05 Jun 2009 06:00 UTC
Issued: Thu 04 Jun 2009 08:40
Forecaster: GATZEN

A level 1 was issued for northern and eastern Spain mainly for large hail and severe wind gusts.

SYNOPSIS

A polar trough is placed over central Europe, and cold air mass has spread across the northern portions. Rather cool air masses are also present over the central and eastern Mediterranean Sea. Warm air mass spreads into the Iberian Peninsula ahead of low geopotential over the Atlantic.

DISCUSSION

Spain

Ahead of the approaching Atlantic trough, a strong mid-level jet spreads across the Iberian Peninsula. The eastern portions will be affected by rather steep mid-level lapse rates and sufficient boundary-layer moisture, and daytime heating will likely result in CAPE. Upslope flow and convergence is expected and thunderstorms are forecast that will be capable of producing severe wind gusts due to mixed low-level air mass and large hail given 10-15 m/s deep layer vertical wind shear. Storms will likely weaken after sunset. Over the northern Iberian Peninsula, steep mid-level lapse rates and some boundary-layer moisture are present, and thunderstorms have already developed on Wednesday evening. On Thursday, QG forcing will be present and thunderstorms will likely develop over the northern portions. Given deep layer vertical wind shear around 15 m/s and also 10 m/s vertical wind shear in the lowest 3 kilometres, supercells may form that will be capable of producing large hail. Severe wind gusts are not ruled out given rather steep lapse rates. Storms may cluster later on when cold pools will develop. Storms may also spread into southern France during the night where isolated large hail is not ruled out given rather strong vertical wind shear.

Northern/central Mediterranean, Balkans

Cool air masses have become unstable over the central Mediterranean, and in the range of low geopotential, thunderstorms seem to be likely. Vertical wind shear will be around 15 m/s in the lowest 6 km, and some storms may organize capable of producing large hail. Best potential seems to exist over northern Italy and the western Balkans. Although a tornado is not ruled out, indications are too weak to issue a level 1.