Storm Forecast
Valid: Fri 10 Jun 2011 06:00 to Sat 11 Jun 2011 06:00 UTC
Issued: Thu 09 Jun 2011 09:31
Forecaster: TUSCHY
A level 1 was issued for E-Bulgaria, E-Romania, Moldova, parts of the Ukraine, all the way up to Estonia mainly for large hail, strong to isolated severe wind gusts and locally excessive rainfall.
A level 1 was issued for N-Algeria and N-Tunisia mainly for large hail, an isolated significant event possible, and severe wind gusts.
A level 1 was issued for W-Turkey mainly for large hail, an isolated significant event possible, and severe wind gusts.
A level 1 was issued for Belgium and the Netherlands mainly for an isolated large hail event.
SYNOPSIS
A strong vortex is situated over UK, Scotland and Ireland with a weaker one centered over far west Russia. In-between, low geopotential heights cover most parts of central Europe. At lower levels, BL moisture is modest with averaged 0-1km mixing ratios below 10 g/kg, increasing a bit from E-Bulgaria towards Belarus.
DISCUSSION
... E-Bulgaria, E-Romania, Moldova, parts of the Ukraine, all the way up to Estonia ...
During the day an elongated N-S aligned convergence zone serves as focus for scattered to widely scattered thunderstorm development. Enhanced BL moisture beneath neutral to weakly enhanced mid-level lapse rates results in 700 to locally up to 1000 J/kg MLCAPE. However, shear at all levels is very weak, so updrafts may struggle to persist for a long period of time. Nevertheless a few large hail and strong downburst events are well possible with stronger thunderstorms. In addition, excessive rain becomes more likely along the western part of the Black Sea, where rapid thunderstorm clustering is forecast. Thunderstorms gradually decay after sunset.
... W-Turkey ...
A weak upper disturbance approaches W-Turkey during the forecast period, resulting in constant cooling at 500 hPa. Also, wind field at mid-levels increases with 15-20 m/s 0-6 km DLS present during the afternoon hours, so a favorable environment for large hail evolves. Thunderstorms develop over far NW-Turkey early in the forecast period and then spread east/southeastwards during the daytime hours. Multicells and isolated supercells occur with large hail forecast and even an isolated significant hail event (larger than 5 cm in diameter) can't be ruled out. Thunderstorms diminish during the night from west to east.
... NE-France, Belgium and the Netherlands...
A strong shear, weak CAPE environment evolves, as intense upper trough axis crosses those areas from the west during daytime hours. Strong forcing spreads east/northeastwards with rapid mid-level cooling and geopotential height falls forecast. Only weak LL moisture return will occur, however this is already enough for low-end instability build up...probably maximized over Belgium and the Netherlands with 200-500 J/kg MLCAPE. There exists a limited time frame between 12-18Z for a few more organized thunderstorms, as 20-25m/s DLS overspread the area and a few stronger updrafts may evolve. Large hail and strong wind gusts will be possible and hence a marginal level 1 was issued. Thunderstorms rapidly decay after sunset.
... UK ...
Mainly daytime driven thunderstorms beneath an upper low are forecast, as 500 hPa cool down to less than -25 °C. Low T-Td spread and more than 50 hPa 0-3 km CAPE indicate the risk for a few funnel/tornado events, especially along any persisting convergence zone. Thunderstorm coverage decreases rapidly after sunset.
... N-Algeria and N-Tunisia ...
Another upper trough affects the N-parts of Algeria and Tunisia, assisting in scattered thunderstorm development during the forecast. A combination of 15-25 m/s DLS, roughly 800 J/kg MLCAPE and more than 250 m^2/s^2 SRH-3 indicate an augmented risk for large to isolated very large hail events, next to isolated severe wind gusts. Thunderstorms keep going well into the night while moving towards the east.
