Storm Forecast
Valid: Fri 08 Aug 2014 06:00 to Sat 09 Aug 2014 06:00 UTC
Issued: Fri 08 Aug 2014 01:23
Forecaster: TASZAREK

A level 2 was issued for France and parts of Benelux mainly for tornadoes, large hail severe wind gusts and excessive precipitation

A level 1 was issued for central and S France, NE Spain, Switzerland and parts of Italy mainly for large hail

A level 1 was issued for France, NE Spain, parts of Benelux and Germany mainly for severe wind gusts

A level 1 was issued for N France and parts of Benelux mainly for excessive precipitation

A level 1 was issued for parts of Sweden and Finland mainly for excessive precipitation

A level 1 was issued for Poland and surroundings mainly for excessive precipitation

A level 1 was issued for parts of Balkan Penninsula mainly for excessive precipitation

SYNOPSIS

Weather in Europe is dominated by two main features: strong trough over NW Europe and ridges of high geopotential field over Russia. This setup provides influx of warm and moist air masses into central European countries and thunderstorms along convergence line from Scandinavia up to Balkans. These storms will remain in low sheared environment and together with low storm motion and high PW values the main threat associated with them will be related to excessive precipitation
and local flash flood phenomena. Most of the unstable air masses over Mediterranean are capped by warm and dry air from Sahara Desert and prevent from convective initiation. Increased probability for the thunderstorms is also expected over N Turkey where weak short wave will provide some QG lift. The most dangerous situation is expected in France where mid and lower tropospheric jet streak will overlap with high boundary-layer moisture and QG-forcing on the cold front heading from west.

...Northern Scandinavia, eastern Poland and surroundings, Balkan countries...

Along a broad convergence zone from Baltic countries to Balkans numerous thunderstorms are expected due to rich boundary-layer moisture, diurnal heating, the plum of cooler mid-level air. Resulting CAPE up to 2000 J/kg in the environment of very weak DLS will prevent from storm organisation into multicells and supercells and thus severe weather phenomena. However, local storm clustering, slow storm motion and PW values exceeding 30mm will increase potential for excessive precipitation and local flash flood phenomena cannot be ruled out. The highest potential for this threat is expected in eastern Poland when PW values are the highest. Rich boundary-layer moisture with PW values up to 30mm, CAPE up to 1000 J/kg and slow storm motion can cause excessive precipitation in northern Scandinavia as well, however this threat seems to be lower than in Poland and Balkans.

...France, Benelux, parts of Germany, parts of Switzerland and Italy...

Rich boundary-layer moisture overlapping with steep vertical lapse rates in central and southern France will result in CAPE exceeding 2000 J/kg and reaching up to 3500 J/kg locally. In the axis of low pressure bay in strong horizontal pressure gradient extending from UK to France, wave on the top of this feature will create good conditions for severe weather phenomena. Although 0-6km shear is expected to be moderate (mainly 15 m/s with 20m/s locally), 0-1km and 0-3km shear due to mid and low tropospheric jet streak seems to be significant. The first one together with low cloud base and moderate instability will point out risk for tornadic supercells. The limiting factor may be associated with the vertical directional wind shear which seems to be not significant (SRH ~ 100m2/s2 mainly with SW flow). Even though, the overlap of LLS amounting 12m/s with mid and low level jet streak and CAPE over 1500 J/kg cannot rule out isolated significant tornado event in central and NE France. Second main threat related to strong 0-3km shear (>15 m/s) overlapping with moderate and high instability may result in quasi-linear convective system moving over central and NE France in NE direction. Sideward and forward storm building may organize convection into bow echo feature and generate severe wind gusts. Embedded and isolated supercells will be also capable of producing large hail and excessive precipitation. The highest risk for flash flood phenomena is located in central, N France and Benelux due to PW values exceeding 40mm. The highest threat for severe weather is expected to start from 15Z when convection will be likely to organize in central and SW part of France and will remain up to 00Z when the system will move in NE direction up to Benelux. Convection forcing sources are predicted from low-level convergence zones over France, potential vorticity advection and cold frontal boundary moving easterly through France and Benelux, and may provide convection up to late night hours.

...North eastern part of Spain...

Locally very strong DLS (> 25 m/s) in the environment of CAPE exceeding 2500 J/kg is predicted S of Pyrenees mountain range. Taking into account also SRH over 200 m2/s2 significant supercells capable of producing very large hail and severe wind gusts are possible. However, since model predicts strong cap (CIN ~ 200 J/kg) south and east of this region, there is high uncertainty whether any convection in this environment will occur. Therefore, only level 1 was issued for this area.