Storm Forecast

Storm Forecast
Valid: Sun 14 Jun 2015 06:00 to Mon 15 Jun 2015 06:00 UTC
Issued: Sat 13 Jun 2015 22:47
Forecaster: TASZAREK

A level 2 was issued for Croatian coast mainly for the large hail, severe wind gusts, tornadoes and excessive precipitation.

A level 1 was issued for Belarus, W Ukraine, Romania, Hungary, W Bulgaria, Slovakia, Czech Republic, Austria, S Germany, Switzerland, C Italy, Greece, FYROM, Serbia, Bosnia, Herzegovina, Slovenia, Croatia and Corsica mainly for the large hail, excessive precipitation and in lesser extent for the severe wind gusts.

A level 1 was issued for France and W Alps mainly for the excessive precipitation.

A level 1 was issued for parts of Russia for severe wind gusts and in lesser extent for tornadoes.


SYNOPSIS

Europe is divided into three main synoptic-scale patterns. Azores high with ridge extending to British Isles together with trough centered over Finland drives advection of cold air masses into N and Central Europe. Peak of the geopotentials long-wave situated over the North Sea will provide lift in the weakly unstable air mass over S Scandinavia. Most of the E, SE and S Europe will be covered with the unstable air masses of tropical origin and rich boundary layers moisture. Mid-level low situated over Portugal will provide lift in some parts of the unstable air over Iberian Peninsula. It is also predicted that short-waves will pass through E and Central Europe, Central Italy and parts of Balkan Peninsula. Most of the thunderstorm threat areas will remain under low-sheared environment with DLS up to 10-15 m/s.


DISCUSSION

...Belarus, W Ukraine, Romania, Hungary, W Bulgaria, Slovakia, Czech Republic, Austria, S Germany, Switzerland, C Italy, Greece, FYROM, Serbia, Bosnia and Herzegovina, Slovenia, Croatia and Corsica...

Thunderstorm activity should start around noon along with the intensifying diurnal heating. In the rich boundary layer's moisture content and lapse rates that locally may exceed 7 C/km, CAPE will grow up to 2500-3000 J/kg. Although DLS in most of the area will be around 10 m/s, thunderstorms due to large CAPE may cluster into multicells. Two short-waves over Slovakia-Hungary-Romania and Belarus-Ukraine should provide persistent lift that together with large instability continuing during the late evening may pose risk for MCS occurrence. The main threats associated with these storms are large hail (mainly due to large CAPE and moist boundary layer) and excessive precipitation (mainly due to slow storm motion and PW exceeding 30mm). Except plausible MCSs, thunderstorm activity should weaken during the evening hours.

...France and W Alps...

Almost stationary thunderstorms are predicted over France and W Alps. Rich boundary layer's moisture (average mixing ratio < 10 g/kg) flowing from the Mediterranean will provide CAPE up to 1000-1200 J/kg. Low-level convergence and favorable QG-lift is predicted to provide persistent convective precipitation that together with low storm motion and PW over 30mm create risk for excessive precipitation and flash flooding.

...parts of Russia...

Although DLS (important factor for convective organization into supercellular thunderstorms) is predicted to be relatively low, the evening overlap of CAPE ~ 1000 J/kg, LLS exceeding 10 m/s and 0-1km SRH over 150 m/s create risk for the tornado occurrence. It is predicted that convection in this region will remain isolated that somehow enhances probability for the tornado occurrence. Lifting mechanism will be present due to short-wave that will pass through this region in the late afternoon hours.

...Croatian coast...

Similar but better conditions in the context of instability and shear are predicted in the late evening and nighttime hours along the Croatian coast. Short-wave that will pass through this area and orographic lift along the coast will be supportive for the CI. DLS exceeding 20 m/s with CAPE over 2000 J/kg and SRH ~ 300-400 m/s provide good conditions for supercellular thunderstorms. Within these type of thunderstorms large hail and severe wind gusts are possible. Strong LLS over 10 m/s and 0-1km SRH up to 200 m/s justify also the threat for the mesocyclonic tornado occurrence. The limiting factor may be the height of the LCL that according to NWP will amount around 1000 m AGL. Thunderstorms are predicted to remain along the Croatian coast since late evening until the end of the forecast period, therefore (due to persistent precipitation) local flash flooding cannot be ruled out.

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