Storm Forecast
Valid: Wed 25 Aug 2010 06:00 to Thu 26 Aug 2010 06:00 UTC
Issued: Tue 24 Aug 2010 21:25
Forecaster: PUCIK

A level 1 was issued for Eastern Belarus, Western Russia mainly for severe wind gusts, tornadoes and large hail.

A level 1 was issued for Baltic States and Southern Sweden mainly for tornadoes and marginally severe wind gusts.

SYNOPSIS

At midlevels, strong zonal flow has established over much of Europe with windspeeds between 20-30 m/s at 500 hPa and around 40 m/s at 300 hPa. Short-wave trough, embedded in this flow should move over Eastern Europe during the forecast period and a slight ridging will be observed over Western Europe. Closer to the surface, deep low pressure system, centered at the beggining over Southern Sweden will move towards the Baltic states. Rather prominent cold front will be associated with this feature, along with frontal trough ahead of the front. Insignificant ridge will stretch from the SW Mediterranean towards Central Europe. To the west, a shallow surface low will affect Southern England and Wales by evening hours.

DISCUSSION

... Eastern Belarus, Western Russia ...

Ahead of the cold front, in the warm sector of the surface cyclone, low-end to moderate destabilisation is predicted to models. While GFS is more optimistic, simulating locally over 1000 J/kg of MLCAPE, ECMWF run from 12 UTC shows only around 500 J/kg of CAPE. Furthermore, models simulate considerable mid and upper level cloudiness in the warm sector, supported by the satellite observations, so surface heating might be limited during the day. Favorable synoptic pattern will establish - with DCVA over the region and in the exit region of the cyclonically curved jet-stream. Along with linear forcing close to the quickly advancing cold front, synoptic-scale conditions seem to be favorable for destabilisation of environment and thunderstorm initiation.

At low levels, prevailing southwesterly to westerly flow is forecast with winds gradually increasing in speed and turning to more southerly direction. Simulated DLS of 20-25 m/s should overlap with unstable region and therefore, well organised storms are forecast, including supercells albeit a quick cold front might favor a squall line mode. Slight chance of large hail or severe wind gusts will exist with stronger, well organised cells. With LLS values approaching 10 m/s in the late afternoon hours and with low LCLs, tornado is not ruled out either, especially if supercellular convection manages to form. Due to the combination of these threats, Level 1 seems to be warranted.

... Baltic states, Southern Sweden...

Close to the center of surface low, low-end instability release is predicted. Due to the favorable forcing and low level wind convergence, abundant low-topped convection might form during the day. Very strong flow at low levels of troposphere, with windspeeds approaching 25 m/s at 850 hPa level should result in high LLS values. With low both LCLs and LFCs, tornadoes might occur, especially on the interface of water/land, where the gradients in windspeed might induce generation of vortices. Marginally severe wind gusts are not ruled out either. Low end Level 1 is issued for this issued due to the combination of aforementioned threats.