Storm Forecast
Valid: Tue 28 Apr 2020 06:00 to Wed 29 Apr 2020 06:00 UTC
Issued: Mon 27 Apr 2020 23:56
Forecaster: DAFIS

A level 1 was issued for SW France mainly for severe convective wind gusts.

A level 1 was issued for Italy and SE France for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for NE Algeria and Tunisia for large hail and severe wind gusts.

SYNOPSIS

Several short-wave troughs can be found in the analysis and forecast maps around a weak ridge that has formed in Central Mediterranean. Two of them will be partly responsible for widespread thunderstorm activity in France, Italy, and Central Europe. A few more PV maxima are placed in the Balkans, Turkey, Russia and southern Sweden where we also expect thunderstorms but most non-severe and pulsating. The strongest overlap of instability and shear is found over France and Italy.

DISCUSSION

.... SW France ....

A PVA is approaching fast from the Gulf of Biscay and will provide synoptic lift to unstable air masses in the morning and afternoon of Tuesday 28/04. CAPE and lapse rates do not look impressive but 500 J/kg MLCAPE and 15-20 m/s DLS suggest that storms will be able to cluster. In fact, AROME shows the formation of a quasi-linear MCS traveling fast east. The main threat will be severe wind gusts but also hail up to 2 cm in diameter cannot be ruled out.

.... SE France and Italy ....

Another short-wave trough is approaching this area and its southern part is associated with a jet streak with up to 35 m/s at 500 hPa increasing DLS up to 20 m/s in Italy. Diurnal heating will result in steep lapse rates in the afternoon and in addition to moist low-level air masses will create a few hundreds of CAPE. Storms will be able to produce large hail or large accumulations of small hail and severe wind gusts. In the northern parts of level 1 shear is weak and 20-25 mm PWAT increases the threat of flash floods during slow-moving storms.

.... Algeria and Tunisia ....

Under the core of a jet streak, CAPE up to 1000 J/kg is forecast and along with veering winds, supercells are expected. PBL will be locally very dry with LCLs above 1500-2000 m, an ideal environment for accelerating downdrafts. Storms will be able to produce large hail and severe convective wind gusts and should dissipate after 18z.