Storm Forecast
Valid: Sat 14 Jul 2018 06:00 to Sun 15 Jul 2018 06:00 UTC
Issued: Fri 13 Jul 2018 20:33
Forecaster: TASZAREK

A level 1 was issued for N Spain mainly for large hail, severe wind gusts and in lesser extent for excessive precipitation.

A level 1 was issued for N Italy, S Austria and Slovenia mainly for large hail severe wind gusts and in lesser extent for excessive precipitation.

A level 1 was issued for NE Poland, Lithuania, W Belarus and NW Ukraine mainly for excessive precipitation, severe wind gusts and in lesser extent for large hail.

SYNOPSIS & DISCUSSION

Rich boundary layer's moisture and warm polar airmass dominate over most of the Europe with small to moderate instability developing within the support of a strong diurnal heating. Weak horizontal pressure gradient stretches from France up to W Russia with the exception of a cut-off placed over Belarus. Majority of thunderstorm activity in this area is expected to occur in the afternoon hours and under weakly sheared environment. Therefore, threat for severe thunderstorm will be rather limited and level 1 is issued only for the area of the cut-off where convective activity will be the most persistent. Isolated pulse thunderstorms and multicell clusters will be capable of producing locally downburst-type severe wind gusts and excessive precipitation. Threat for large hail will be limited due to lack of steep lapse rates and sufficient vertical wind shear, but local events of hail up to 2-3 cm cannot be ruled out as a result of enhanced thermodynamic instability (~ 1500 J/kg ML CAPE).

Broad ridge with strongly capped tropical airmass is located over N Africa and parts of Mediterranean. Jet stream stretching from Azores to Greece divides this airmass from cooler polar air further north. Majority of area covered with the jet features strong convective inhibition preventing from CI. Northern peripheries of the jet over N Spain and N Italy where CI is expected to occur may benefit from 15-20 m/s DLS. This can provide better storm organization and thus higher threat for severe thunderstorms.Supercells capable of producing large hail and severe wind are possible. Persistent thunderstorm activity within mountain zone cannot also rule out excessive precipitation and local flash flooding event. The main limitation for N Spain is uncertain CI while level 1 over Alps features limited thermodynamic instability.

Most of the thunderstorms in Europe should fade in the late afternoon and evening hours except N Spain, France, Alps and cut-off over NE Poland and W Belarus where lightning activity may remain during nighttime.