Valid: Sat 01 Oct 2016 06:00 to Sun 02 Oct 2016 06:00 UTC
Issued: Fri 30 Sep 2016 22:49
A level 1 was issued for parts of W Mediterranean mainly for large hail, excessive precipitation and in lesser extent for severe wind gust.
A level 1 was issued for NW Russia mainly for severe wind gusts and in lesser extent for tornadoes.
SYNOPSIS and DISCUSSION
SLP without any well-pronounced highs and lows decreases along with increasing latitude. Resulting strong westerly zonal flow dominates over most of the Europe. The most significant wind speeds exceeding 25-30 m/s at 500 hPa are located over Baltic Countries, W Russia, France, Benelux and Germany. Two waves are expected during a forecast period. First, larger but with weaker horizontal pressure gradient travels through W Mediterranean and W Europe. Second wave, smaller but with more dynamic air field and higher values of low and mid-level wind shear travels through Baltic Countries and NW Russia. Both features triggers thunderstorm formation.
High-shear/low CAPE/low-topped convection with strong QG-forcing will occur over NW Russia. Within 400-600 J/kg CAPE and ~ 15 m/s MLS, convection may cluster into lines with bowing segments where severe wind gust are possible. Given 200-300 m2/s2 SRH and 10 m/s LLS, one or two low-topped isolated supercells capable of producing severe wind gusts are possible. Short-lived weak tornado within these cannot be ruled out, however they are less likely due to small thermodynamic instability in lowest levels.
Low 200-400 J/kg CAPE with moderate to high MLS is predicted over W and parts of CNTRL Europe. Although forcing will be not as impressive as in NW Russia, few thunderstorms with some severe wind potential are possible in the afternoon hours. Strongest thunderstorms with a potential of producing severe weather are possible in the W parts of Mediterranean. Under influence of the passing wave, a mixture of S advection of 12-14 g/kg mixing ratios and > 7 K/km lapse rates will produce locally a CAPE up to 1500-2500 J/kg. Within this environment, a DLS of 15-20 m/s will be sufficient enough to organize convection into multicell clusters and supercells capable of producing large hail and excessive precipitation (PW ~ 35-40 mm). Severe wind gust potential within microburst/downburst cannot be ruled out as well. Eastwardly moving thunderstorms should reach W Italian coast in the late afternoon hours and maintain their lightning activity during nighttime.