Storm Forecast
Valid: Tue 31 May 2011 06:00 to Wed 01 Jun 2011 06:00 UTC
Issued: Mon 30 May 2011 22:12
Forecaster: TUSCHY
A level 1 was issued for parts of Germany and NE-Switzerland mainly for large hail, strong to severe wind gusts, excessive rainfall amounts and an isolated tornado event.
A level 1 was issued for parts of Sweden mainly for large hail, strong to severe wind gusts and an isolated tornado event.
A level 1 was issued for NE-Algeria mainly for large hail and strong wind gusts.
SYNOPSIS
An upper trough drops southwards over UK/France with cut-off process underway during the night hours. East and south of this feature, no stout ridge is seen in geopotential height fields, which allows widespread thunderstorm development over most parts of Europe.
At lower levels, strong high pressure builds in from the west, affecting France during the day. Otherwise, warm and moist BL features favorable support for modest CAPE over an extensive area.
DISCUSSION
...Germany and NE-Switzerland 09 Z - 18 Z...
At Monday 21 Z, numerous clusters of loosely organized thunderstorms affected CNTRL/E-France with extrapolated motion indicating nighttime storms/showers probably over Benelux/SW/S and W-Germany. This will be important for todays activity regarding insolation, PBL moisture and hence initiation. Would not be surprised to see storms further west during the morning, including W/NW-Germany with weak CIN/subtle PVA maxima allowing thunderstorm initiation already in the morning/ during forenoon.
Thereafter, focus shifts further east as convergence zone/cold front gradually shifts eastwards. Currently, no hints on anvil debris are present, so a couple hours of diabatic heating are forecast in prefrontal warm sector. BL stratification again not reliable with certain models, but Tds in the lower tens are well possible with places of mid tens plausible with moisture pooling along convergence zone. Also, strong frontogenetic signals over E-Germany (in conjunction with developing surface low pressure channel from NE-Germany to N-Austria) indicate a good chance for rich BL moisture with attendant better CAPE.
Overall, CAPE fields look the best over NE/E and SE Germany with MLCAPE of roughly 500 J/kg. Also added N-CNTRL Germany to better thermodynamic environment with somewhat steeper mid-level lapse rates. Instability wanes west of the cold front, however some MUCAPE remains present.
Upper streamline pattern features good divergence within right entrance region. Main concern for severe storms from noon onwards exists over N-CNTRL/N/NE Germany, where 20 m/s DLS and modest CAPE overlap...some veering present, too. Large hail and strong wind gusts will be the main risk. An isolated tornado can't be excluded along wind shift zone, where enhanced LL CAPE evolves, especially in the northern part of the level 1. Thunderstorms exit to the NE after 18 Z. Further south, by name E-Germany, modest CAPE and strong anvil layer flow also support a few severe thunderstorm events with hail and strong wind gusts. Betimes, flash flooding becomes an increasing concern with slow storm motion and PW at or above 30 kg/m^3. Over SE-Germany, rapidly clustering thunderstorms evolve around noon onwards with isolated large hail and excessive rainfall amounts. Overall wind field remains too weak for organized updrafts ove far SE Bavaria with a few multicells possible further to the west (including NE-Switzerland).
... S/E Germany 18 Z to 06 Z ...
After sunset, evolving cut-off over SE-France and potential weak cyclogenesis over the Czech Republic assist in strengthening WAA atop cool BL (forced by cold pools from daytime convection and ongoing LL-CAA). Hence, convective QPF signals gradually decay with the evolution of a broad stratiform rain shield somewhere from SW-Germany to E-Germany. Not yet clear how much MUCAPE will be available, but a few embedded thunderstorms are still possible. Excessive rainfall will be the main hazard.
... SE-Sweden ...
Well defined warm front crosses the highlighted area during the morning hours from the south, so a warm and moist warm sector is present around noon onwards. Not much lift is needed for initiation (provided by numerous vorticity maxima), so scattered thunderstorms are forecast between 12 and 21 Z. Speed shear is more the adequate for multicells/a few supercells as 0-6 km bulk shear increases to 20-25 m/s and marginal weaker 0-3 km shear exists. Magnitude of the SRH depends on how strong LL depression further north deepens, but right now, straight hodographs with splitting cells are forecast. Large hail, strong to severe wind gusts and an isolated tornado event wil be the main hazard. Thunderstorms gradually decay after sunset.
... N-Algeria ...
An upper wave moves eastwards along the coast of Algeria. Forcing, weak capping and modest shear allow multicells with isolated large hail and strong wind gusts. Thunderstorm activity is forecast all day long with main activity offshore during the daytime hours and increasing activity onshore during the night, as LL moisture moves further to the south.
Otherwise, weak shear precludes further risk areas for organized convection. However, an isolated large hail/strong downburst event is well possible, especially over NE Croatia / W-Hungary (up to 1000 J/kg SBCAPE).
