Storm Forecast
Valid: Mon 08 Feb 2010 06:00 to Tue 09 Feb 2010 06:00 UTC
Issued: Sun 07 Feb 2010 20:43
Forecaster: TUSCHY

A level 1 was issued for SW-Turkey mainly for an isolated waterspout and large hail event.

A level 1 was issued for the coastal areas of NE-Morocco and NW-Algeria mainly for tornadoes, severe wind gusts and large hail.

SYNOPSIS

Numerous troughs with short wave lengths rotate over the Mediterranean, south of the European polar vortex. Hence, the main activity will be found over the Mediterranean. An isolated, short-lived thunderstorm is also forecast along the west-central coast of Norway due to impressive mid-level lapse rates / T-500hPa at or below -40°C/ and somewhat better LL moisture along the coast.

DISCUSSION

... S-Turkey ...

An upper trough / broad surface depression levels off while lifting to the north. Near surface trajectories veer to southwest, so somewhat higher mixing ratios will be achieved in the lower troposphere. Especially during daytime, a more normal component of the LL flow causes orographically enhanced precipitation ( Antalya eastwards ), so locally 30-70mm/12h are well possible along the coast. Neither dynamics, nor the increasingly more parallel near surface flow later-on point to a more robust rain event.

Further west, cold thermal trough weakens, but causes enough SBCAPE build-up atop the warm Aegean Sea for scattered to widespread showers/thunderstorms. In addition, a cold front surges SE-wards during the day and decays somewhere over the SE-Aegean Sea. This front causes a gradual decrease in activity from NW to SE. After sunset, another upper impulse emanates from Greece. Despite steepening lapse rates, this feature will pass mainly north of the stalling surface front, so convection will mainly increase along this baroclinic zone - over the S-Aegean Sea. The severe risk is conditional at best : isolated waterspouts along the SW/-coast of Turkey and marginal hail during the daytime hours and a severe wind gust risk over the S-Aegean Sea after sunset as DLS increases to 20-25m/s. We went with a marginal level 1 along the SW-coast.


... Iberian Peninsula and the W-Mediterranean ...

A new impulse works its way into SW-Europe with surface pressure falling over the western Mediterranean. A plume of subtropical air advects northeastwards towards the developing depression, which covers an area south of Spain until sunset. That's the time, when a strong mid-level jet approaches from the NW next to a stout PVA max from the west, so thunderstorm probabilities will increase rapidly from west to east between 18-21 UTC. The level 1 region will be the focus for organized convection as a coastal front/weak cold front resides parallel to the coast of NE-Morocco/NW-Algeria. At the same time, winds at all levels increase (e.g. 850hPa to 25m/s) and a sharp directional shear gradient evolves along the coast. Good LL CAPE, and aforementioned shear indicate a good set-up for a few tornado reports, severe wind gusts and isolated large hail.

Over Portugal, daytime driven thunderstorms are forecast, with peak time between noon and sunset. Mid-levels are not that cold but maritime air mass and some diurnal heating will be enough for scattered showers/thunderstorms with isolated large hail and a tornado along the coast, despite very short and straight hodographs. We think that the most vigorous convection will evolve over S-Portugal, which will be under good upper divergence (left exit of mid-level jet).