Storm Forecast
Valid: Sat 24 Aug 2019 06:00 to Sun 25 Aug 2019 06:00 UTC
Issued: Sat 24 Aug 2019 00:33
Forecaster: PISTOTNIK

A level 1 is issued for NW Russia mainly for severe convective wind gusts, large hail and tornadoes.

Level 1 and level 2 areas are issued for parts of NE Algeria, NW Tunisia, Corsica, Italy, Austria, Slovakia, Slovenia, Croatia, Bosnia-Herzegovina, Montenegro, Albania, NE Turkey, Georgia and SW Russia mainly for excessive convective precipitation and large hail. In addition, non-mesocyclonic tornadoes (waterspouts) are possible in coastal areas.

SYNOPSIS

The main frontal zone runs across N Europe. An embedded short-wave trough exits into Russia. Another one amplifies over the North Atlantic. In-between, a shallow ridge extends into Scandinavia.
Further south, very warm to hot air covers most of Europe under weak pressure and temperature gradients. Near the surface, an extensive anticyclone is centered over Belarus.

DISCUSSION

... NW Russia ...

Diurnal heating and lift ahead of the short-wave trough create a few hundred J/kg of CAPE at the southern flank of a filling cyclone. The southern part of the unstable air overlaps with moderate vertical wind shear (10-15 m/s across the 0-3 km layer, 5-10 m/s across the 0-1 km layer) and slightly veering profiles (0-3 km storm-relative helicity around 100 m^2/s^2). Scattered showers and low-topped thunderstorms will form especially in the noon to afternoon hours and organize into multicells. A low-end level 1 covers a risk of marginally severe hail and wind events, especially in case a few transient supercells can form.

... other thunderstorm areas south of 50N ...

Warm and moist air and strong insolation under quiescent synoptic conditions allow the build-up of CAPE on the order of 500-1500 J/kg over land and up to 3000 J/kg over the Ligurian, Tyrrhenian, Adriatic, Black and Azov Sea (as shown by the Fri 12 UTC Brindisi and Tuapse soundings). Scattered thunderstorms will form especially over orographic features in the afternoon and evening. Single cells or multicells will be the dominant storm mode, and upscale growth into a few larger clusters with erratic, outflow-driven motion is possible. Localized excessive precipitation and moderately large (2-4 cm sized) hail are the main risks. The richest low-level moisture is present in the level 2 areas and ready to be ingested into upslope circulations, creating a particularly dangerous setup for flash floods.
Storms propagating to coastal and offshore areas along nocturnal land breeze fronts may spawn some waterspouts.

Forecast models show robust CAPE as far north as central Germany, the Czech Republic, or the central and E Ukraine, but in the absence of synoptic lift mechanisms, convective initiation is not too likely over flat terrain.