Storm Forecast
Valid: Thu 21 Apr 2011 06:00 to Fri 22 Apr 2011 06:00 UTC
Issued: Wed 20 Apr 2011 13:06
Forecaster: SCHLENCZEK

A level 1 was issued for Iberia mainly for large hail and severe wind gusts.

A level 1 was issued for the N Maghreb States mainly for large hail and severe wind gusts.

SYNOPSIS

A blocking high is present over the central parts of Europe, leading to stable conditions in most places. The greatest chance for some organized convective storms is anticipated for the Iberian Peninsula and N Morocco / N Algeria ahead of an upper cut-off low. Another cut-off low over the E Mediterranean translates slowly eastwards.

DISCUSSION

...Spain and Portugal...

In the southern parts of Spain and Portugal, some low-end instability is present ahead of an approaching upper trough. MLCAPE in order of 300 - 500 J/kg is forecast which coincides with 15 - 20 m/s deep layer shear. 0-3 km shear is in order of 15 m/s and locally enhanced SRH may allow some organized multicells and / or supercells which could produce some isolated large hail and severe wind gusts. Convective initiation should be almost certain as QG lift ahead of the trough should be strong enough to overcome the small CIN barrier. The greatest chance for a severe thunderstorm should be present during the afternoon / early evening hours, shortly after initiation took place when most storms are still discrete. A low-end level 1 should be warranted.

...N Morocco, N Algeria...

The situation further southeast is similar compared to Iberia. Some layers of dry air in the mid troposphere may allow severe wind gusts due to evaporative cooling of the downdraft and if a storm contains a mesocyclone, isolated large hail should be possible as well.

...France, Benelux, Germany, British Isles...

Within the upper ridge, local spots of slightly augmented LL moisture and convergent LL flow are found where some low-end CAPE may be created by diurnal heating. As vertical shear is almost zero in most of these places, storms should be poorly organized and severe weather is unlikely. One can't rule out an isolated hail / wind gust event but this is likely below the level 1 threshold.

...E Mediterranean...

In the vicinity of another upper low, some CAPE is present in a weakly sheared environment. Showers and thunderstorms which may develop during the day are likely to be non-severe.