Storm Forecast Valid: Tue 26 Aug 2014 06:00 to Wed 27 Aug 2014 06:00 UTC Issued: Mon 25 Aug 2014 21:17 Forecaster: SCHLENCZEK
A level 2 was issued for E France and S Germany mainly for tornadoes and severe wind gusts.
A level 1 was issued for NE/E France, Belgium, Luxembourg, S-central Germany and W Czech mainly for severe wind gusts and to a lesser extent for tornadoes.
A level 1 was issued for S UK for a chance of tornadoes.
A level 1 was issued for parts of the North Sea and Baltic Sea for spout-type tornadoes.
SYNOPSIS / DISCUSSION
... SE UK, NE / E France, SW / central Germany ...
A dissipating low pressure system over the British Isles which continues eastwards advects warm and unstable air into W / central Europe. A few hundred J/kg of SBCAPE are forecast consistently in the warm sector by the past runs of GFS and ECMWF, at least partly overlapping with 15 - 25 m/s of 0-6 km bulk shear. T/Td is forecast around 20/16 °C for SW Germany which leads to low LCL heights. Convection should fire up in the late morning / early afternoon hours even though there is some subsidence over the central parts of Germany from the upper ridge. Combined with enhanced LL shear and SRH1, this may allow a few tornadoes. Further north, LL shear is weaker but the background wind field should be intense enough to support isolated severe wind gusts mainly from downward transfer of momentum. Local heavy precipitation is possible but fast storm motion should preclude a risk of flooding in most cases.
Over UK, there is very weak LL shear forecast in the afternoon hours but a weak background flow should support some spout-type tornadoes.
... N Germany, Denmark, N Poland, S Scandinavia and Baltic Sea region...
Sufficient buoyancy and weak background winds enhance the chance for long-lasting convergent flow in the vicinity of convective storms and may lead to funnels which could end up in spout-type tornadoes. The greatest chance for landspouts / waterspouts exists around Denmark and N Poland. Further north, deep layer shear is also quite weak but the stronger background flow will likely disturb the formation of funnels / tornadoes.
Some regions with locally enhanced LL shear exist over Finland but overall instability is likely too low to support a tornado threat covered by a LVL1.
... NW Italy and Mediterranean Sea...
A plume of unstable air is advected from the Balearic Islands towards Italy. It will likely remain strongly capped but in case of convective initiation, isolated storms may profit from 20 - 25 m/s of 0-6 km bulk shear and could develop mesocyclones. Overall threat is likely too marginal for a threat level as the capping inversion is likely too strong for storm development.