Storm Forecast
Valid: Sat 21 May 2016 06:00 to Sun 22 May 2016 06:00 UTC
Issued: Sat 21 May 2016 06:29
Forecaster: TASZAREK

A level 2 was issued for W France and part of Belgium mainly for severe wind gusts, large hail and tornadoes.

A level 1 was issued for W France, Benelux and N Spain mainly for severe wind gusts nad large hail.

A level 1 was issued for NW Greece mainly for excessive precipitation.

SYNOPSIS

Severe and extremely severe thunderstorms are possible over W France and Benelux. A long wave trough with well defined southern warm and moist air advection on its eastern flank is approaching W Europe. Within a diurnal heating of low-levels rich in moisture, a broad area of developing instability over France will be almost fully covered with eastern side of the cyclonically curved jet stream. Therefore, warm section with unstable air mass will be almost fully covered with DLS of around 20-25 m/s and remain under a QG-lift. Thunderstorms are also likely within a cut-off placed over Greece and trough in W Russia. Due to a local increase in weak instability, thunderstorms in weakly sheared environment are also not ruled out in Poland, W Ukraine, Slovakia, Alps, Romania, Serbia and parts of Sweden, Finland and Baltic Countries. Ridge over W Mediterranean inhibits any convective activity over this area.

...W Europe...

A broad area of 7-7.5 K/km lapse rates overlaps with rich boundary layer's moisture (ML mixing ratios ~ 10-11 g/kg) and results in a CAPE up to 1000-1500 J/kg, locally over CNTRL and SW France even with 2000-2500 J/kg. Although a magnitude of QG-lift is not impressive and part of the airmass remains capped, it is fully covered with DLS up to 20-25 m/s, which means that any thunderstorm developing in such environment may quickly become severe. Thanks to southern moist low-level inflow, NWP models predicts SRH up to 100-200 m2/s2 that involves a threat for supercells capable of producing large hail and severe wind gusts. However, due to an M-shaped hodograph and rather parallel vertical wind profile, supercells may be more likely to cluster into a linear feature (squall line) with a more pronounced threat for severe wind gusts. It is also important to mention that CNTRL and N France will be under favourable tornado parameters with LCL below 800m AGL, LLS exceeding 10 m/s and 0-1km SRH over 100 m2/s2. Therefore, a significant tornado event cannot be ruled out within any of the isolated supercells that will form in northern part of level 2 threat area. CI should take place in the late afternoon hours around 16-18UTC and up to evening cluster into two MCSs, one over SW France and second over N France trough Benelux. A large hail and severe wind gusts will be the main threats. MCS with active lightning will continue to move to NW Germany into nighttime hours. A large hail and severe wind gust threat exists also over N Spain where a steep lapse rates will overlap with > 20 m/s DLS and 600-800 J/kg CAPE.

...SE Europe...

Another area of interest with a risk of widespread thunderstorms covers SE Europe where a cut-off is placed over Greece and Aegean Sea. Although most of the areas are covered with weakly sheared environment, a locally enhanced DLS up to 15 m/s over ~ 1000 J/kg CAPE may result in local storm clustering into multicells and pose a threat of small hail and isolated wind gusts. Over Greece where a storm motion will be the smallest and convection will remain stationary near mountains, a high amounts (50-70 mm) of convective and large-scale precipitation are not ruled out. Although a local flash flooding event is possible, a factor that limits a risk is mainly related to rather not impressive values of PW (20-25 mm).