Storm Forecast
Valid: Wed 20 Apr 2011 06:00 to Thu 21 Apr 2011 06:00 UTC
Issued: Tue 19 Apr 2011 23:04
Forecaster: KOROSEC

A level 1 was issued for parts of Iberian Peninsula mainly for large hail and locally strong wind gusts.

A level 1 was issued for parts of northern Algeria and NE Marocco mainly for large hail and damaging winds.

SYNOPSIS

The focus for today's convective activity will be the persisting upper low located near the western Iberia. At surface, a cyclone with a well-defined front will be pushed further east towards the peninsula. A plume of EML will be rather quickly advecting NNE-wards into SW Europe, creating an unstable environment.

The rest of Europe will remain warm and stable, with only sparks of low convective weather probabilities over west-central Alps and SW-ern Turkey.

DISCUSSION

... Portugal and south-western Spain...

Beneath the strong EML, characterized by steep mid-level lapse rates, additional moistening will be on going across Iberia. This will result in moderate instability, yielding MLCAPEs in excess of 1000 J/kg locally. Storms will likely initiate along the local prefrontal convergence lines as well as near the front later. In moderately sheared environment (15-20 m/s of deep layer shear) and favorable veering profiles (100-200 m^2/s^2 of SREH3), storms will gain organization in multicells and possibly also into a supercell or two. Those will pose a threat for large hail and locally some strong winds given the dry mid levels. Expect storms to last well into the early night near the surface front in SW Iberia. Intense rain might become a threat if cells could persist over the same areas for longer time.

... northern Algeria and NE Marocco ...

Later in the afternoon hours, a weak secondary surface low forms over NW Africa and moves NE-wards across northern Algeria. This will result in backed near-surface flow from the Mediterranean inland into Algeria. With combination of very steep lapse rates above it, storms will initiate along the cold frontal convergence. Being placed under the upper level divergence, at least moderate ascent/forcing will help triggering and organizing storms in rather strongly sheared environment. Large hail (up to 3-4 cm in diameter) and strong wind gusts will be the main threat with these organized storms. As the low tracks further NE in the evening hours, storms could continue off the coast of northern Algeria in the night hours, merged into a small convective system.