Storm Forecast
Valid: Sat 30 Jun 2018 06:00 to Sun 01 Jul 2018 06:00 UTC
Issued: Sat 30 Jun 2018 00:40
Forecaster: TASZAREK

A level 2 was issued for parts W Russia mainly for large hail, severe wind gusts, excessive precipitation and tornadoes.

A level 2 was issued for parts of SW Russia mainly for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for parts of E Europe mainly for large hail, severe wind gusts and excessive precipitation.

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

A level 1 was issued for parts of W France, NW Spain and N Portugal mainly for large hail, severe wind gusts and excessive precipitation.

SYNOPSIS & DISCUSSION

Europe is dominated by a long and narrow ridge extending from NW Africa through France and up to Norwegian Sea. It divides a small and sharp long-wave near Iceland and almost stationary cut-off low over W Iberian Peninsula from a broad and deepening long-wave covering parts of CNTRL and E Europe. Jet streaks are located over Iberian Peninsula, corridor from N Scandinavia to Romania, and corridor from SW Russia to NW Russia. A well-developed warm sector with moist and unstable airmass is located on the eastern flank of an eastwardly moving long-wave.

Within moisture convergence zone and strong diurnal heating, surface-based thunderstorms are expected to develop along surface trough and frontal boundary in the afternoon hours. Although ML CAPE will be ranging from 1000 to 2000 J/kg, support of >15 m/s DLS, >10 m/s LLS and strong QG-lift will allow for convection to organize into multicell clusters and supercells capable of producing large hail, severe wind gusts and heavy rain. Threat for large hail will be partly limited by lack of steep lapse rates in mid-levels. Veering vertical wind profiles and LCL decreasing towards evening hours cannot rule out a tornado event, especially given strong LLS and the occurrence of an isolated supercell. Convection is likely to cluster into MCS moving further NE during late evening and nighttime hours.

Another zone where severe thunderstorm are expected to develop (very late CI) are parts of SW Russia. In the environment of rich boundary layer's moisture (> 12 g/kg MIXR), steep lapse rates (> 7 K/km) and > 20 m/s DLS thunderstorms including multicell clusters and discreet supercells will be developing along convergence zone after 18 UTC. Within these storms, >5 cm large hail and severe wind gust events cannot be ruled out. Tornado threat should be limited due to high LFC. Storms over Russia in the warm sector should maintain their vivid lightning activity during nighttime hours.

Thunderstorms developing in the weakly sheared environment along frontal boundary and within warm sector over Balkan Peninsula should start in the afternoon hours and fade in the late evening. Although their severe weather potential will be generally low, a local severe wind, large hail and especially excessive precipitation event cannot be ruled out.

Thunderstorms over eastern flank of a stationary cut-off (NW Iberian Peninsula) should initiate in the early morning hours and maintain their activity until evening moving offshore and towards W France during nighttime. Although instability will be rather small (ML CAPE 400-800 J/kg), steep lapse rates and > 20 m/s DLS cannot rule out a few supercells capable of producing large hail and severe wind gusts.

A small probability for severe thunderstorms exists also over parts of S Austria, NE Italy and Slovenia, where within approaching minor short-wave, enhanced DLS and steep lapse rates a few large hail and severe wind gust events are possible to occur.