Storm Forecast
Valid: Tue 11 May 2021 06:00 to Wed 12 May 2021 06:00 UTC
Issued: Mon 10 May 2021 21:23
Forecaster: DAFIS

A level 1 was issued for parts of NE Spain, S France and Italy mainly for excessive convective precipitation, large hail and severe convective wind gusts.

A level 1 was issued for the UK mainly for severe convective wind gusts.

SYNOPSIS

A deep trough in western Europe has a positive tilt and brings very warm and moist air masses over central Europe. By the end of this outlook, this trough will progressively acquire a negative tilt and will break into two main PV maxima, with one of them forming a cut-off low over Italy. Another cut-off low exists in W Russia and slowly travels west, over Ukraine, but is accompanied by dry low-level air masses and instability is weak.
The main hot spots for DMC on Tue 11/05 will be in North Mediterranean and the UK, where there is an important CAPE and shear overlap. Also, NE France, Benelux and Czech Republic may experience DMC events, but the mid-level WAA limits CAPE, and CIN creates questionable conditions for CI.

DISCUSSION

.... Spain, France, Italy ....

Under the influence of the long-wave trough, steep lapse rates and unstable low-level air masses in the Mediterranean create favorable conditions for thunderstorms. More specifically, the conditions in NE Spain and SE France will be the most favorable for large hail events, with steeper than 7 K/km 800-600 hPa lapse rates, MLCAPE up to 800-1000 J/kg and DLS stronger than 15 m/s.

DLS will be even stronger over Italy, but the rest of the ingredients will be limited for large hail, yet storms will be able to become severe close to the coasts. The main threats in Italy will be severe convective wind gusts and excessive precipitation.

... UK ...

An embedded short-wave trough within the core of the long-wave trough in western Europe, will create favorable conditions for storms in the UK. Synoptic lift of unstable air masses ahead of this trough will initiate storms just after noon, coinciding with the maximum of diurnal heating. A mid/low-level jet and slightly veering winds will create SREH and most importantly, 0-1km SREH in the most SW parts of the Level-1 area may increase the chances for some brief landspouts. For the rest of the areas, severe wind gusts will be the main threat.