Storm Forecast
Valid: Fri 06 Apr 2018 06:00 to Sat 07 Apr 2018 06:00 UTC
Issued: Fri 06 Apr 2018 00:00
Forecaster: PISTOTNIK

A level 1 is issued for parts of Bulgaria for large hail.

A level 1 is issued for E-central Spain mainly for large hail.

SYNOPSIS

An ill-defined omega pattern establishes over Europe. Long-wave troughs are placed over eastern Europe and over the eastern Atlantic near Ireland and Portugal. In-between, mid-level ridging extends from the central Mediterranean region into central Europe, and a large surface high forms which is centered over Poland.

DISCUSSION

... SE Europe ...

Diurnal heating and large-scale lift ahead of the diffuse trough axis will allow scattered afternoon thunderstorms over hilly and mountainous terrain in Romania, Bulgaria, FYROM, Greece and W Turkey. The majority of storms will be non-severe.
Isolated large hail is possible towards the southeast, where CAPE can locally exceed a few hundred J/kg (as an elevated mixed layer is advected off the Turkish highlands) and 0-3 km shear may rise to 10-15 m/s (under the influence of thermally induced upslope flows). However, capping will also be stronger in the areas with better wind profiles. A small level 1 is issued for parts of Bulgaria, where confidence in convective initiation overlaps with slightly enhanced vertical wind shear. Initation is less likely over NW Turkey (it is suggested by ECMWF in the evening, but not backed up by other models) under otherwise similar conditions in terms of CAPE and shear.

... Spain and France ...

A few hundred J/kg of CAPE will build in the strong warm air advection regime ahead of the western trough. Convective initiation will be delayed by the capping inversion and by the late arrival of synoptic lift support, but in the afternoon or evening scattered thunderstorms should form over the mountains of central Spain and move NNE-ward. 0-3 km shear (10-15 m/s) and storm-relative helicity (100-200 m2/s2) support multicellular organization, and one or two supercells are not ruled out. Large hail is the main risk. In case a larger cluster evolves, isolated severe wind gusts or flash floods are not ruled out, either.
Elevated storms may drift over the Bay of Biscay, W France and Catalonia overnight, but severe weather is unlikely then.