Storm Forecast
Valid: Sat 25 Jul 2015 06:00 to Sun 26 Jul 2015 06:00 UTC
Issued: Sat 25 Jul 2015 04:52
Forecaster: DAFIS

A level 2 was issued for NE Poland, SE Lithuania and parts of Belarus mainly for severe wind gusts, excessive rain, hail and tornadoes.

A level 1 was issued for a large part of the continent, from N Italy to Denmark and Baltic states mainly for severe wind gusts, excessive rain, hail and to a lesser extent tornadoes.

SYNOPSIS

An unsual, for this time of the year, weather pattern is formed in Europe. A strong cyclogenesis takes place in North Sea and moves quickly eastwards, affecting several countries with severe wind gusts, excessive rain and possible tornadoes. Jet stream is unusually far south tomorrow, assisting a Shapiro-Keyser cyclogenesis with probably a sting jet event, but this is much less common during summer conditions.
As far as the rest of Europe is concerned, a wide ridge affects E-NE Europe (Russia) where favorable convective conditions appear on Sunday. Southern parts of the continent are under quite unstable conditions and diurnal heating will lead to scattered thunderstorms at the second half of Saturday.


DISCUSSION

....NE Poland, SE Lithuania and Belarus....

A level 2 was issued for these countries, especially for late afternoon hours when the cold front pushes very humid and unstable LL air masses towards Lithuania and Belarus until night hours. There are marginal signals of rather high 0-3km wind shear over Poland that exceed 20m/s (according to GFS), there is a great probability of a strong squall line formation over Poland, which will be driven NE later on, with severe wind gusts and excessive rainfall being the main threats, as PW exceeds 40mm.
After 18z global and high resolution models predict strong LLS conditions, with more than 15m/s of 0-1km wind shear overlapping with CAPE across most of Poland and very low LCLs (<600m). The aforementioned squall line would be able to produce tornadoes under this environment, especially in NE Poland.

....Level 1 area....

The main question about this area is its NW parts, where the LL vortex has its maxima during the night of Saturday. GFS and ECMWF agree to a 990hPa low centre over Denmark and taking into account the warm-season thermodynamics (high MUCAPE etc), severe events may take place. Non-convective severe wind gusts (>30m/s) are forecast for the Netherlands, Denmark and N Germany during the afternoon and in southern parts, scatter thunderstorms may become severe where DLS is around 20m/s and severe wind gusts are expected due to LL dry air.
North Italy is under mid layer cool conditions and DLS around 15m/s may sustain some clusters of storms for several hours and excessive rainfall and/or hail is forecast.
A low tornado threat is present in level 1 area, mainly at the southern parts of level 2 and in NW Poland where low LCLs (<600m) and enhanced LL shear (10-15m/s) overlap.