Storm Forecast
Valid: Sat 06 May 2017 06:00 to Sun 07 May 2017 06:00 UTC
Issued: Sat 06 May 2017 06:59
Forecaster: TASZAREK

A level 1 was issued for E Poland, W Ukraine and N Romania mainly for the large hail, excessive precipitation and severe wind gusts.

A level 1 was issued for N Mediterranean area for the possibility of severe wind gusts, excessive precipitation, and in lesser extent for large hail and tornadoes.

SYNOPSIS

Most of the CNTRL, E, SE and S Europe is covered within the polar airmass of marine origin and stays under weak horizontal pressure gradient. Weakly pronounced mid-level trough travels through CNTRL, E and SE Europe and within diurnal heating and moisture pooling supports the development of DMC on its eastern flank, mostly in the weakly sheared environment. Thunderstorm activity is also possible in the cold sector behind the cold front and within the passage of the shortwave in the axis from S France up to Croatia. The latter will receive the support of a strong QG-lift and with enhanced wind shear and helicity may result in a low-topped supercells capable of producing severe weather.

DISCUSSION

...E Poland, W Ukraine and N Romania...

Diurnal heating and moisture pooling enhances mixing ratios to ~ 10 g/kg and within ~ 7 K/km lapse rates develops CAPE up to 1000-1500 J/kg (GFS scenario). CI is expected in the typical 14-16 UTC afternoon hours and thunderstorms should remain until late evening hours. Although wind shear is very weak, slowly northerly moving pulse thunderstorms may be capable of producing heavy precipitation, large hail (strong lapse rates and enhanced instability) and microburst type severe wind gusts.

... N Mediterranean area...

Within the passage of the shortwave trough, a rather small instability up to 200-400 J/kg develops on the eastern flank of the wave. However, thanks to strong QG-lift, 25-30 m/s DLS and decent 250-350 m2/s2 SRH any thunderstorm developing in this environment may evolve into low-topped supercell capable of producing severe wind gusts, heavy rain, large hail and in lesser extent tornadoes (given > 10 m/s LLS). The highest probability for severe weather falls on the late afternoon and evening hours in Corsica and parts of Italy. The amount of available instability is the main uncertainty and limiting factor.