Storm Forecast
Valid: Fri 28 May 2010 06:00 to Sat 29 May 2010 06:00 UTC
Issued: Thu 27 May 2010 20:25
Forecaster: TUSCHY

A level 1 was issued for parts of the Ukraine, Hungary, Moldova, E-Romania and E-Slovakia mainly for excessive rainfall and large hail.

A level 1 was issued for W-Poland, N-Czech Republic and E-Germany mainly for large hail and to a lesser extent for tornadoes.

A level 1 was issued for parts of Austria mainly for excessive rainfall.

A level 1 was issued for parts of Denmark mainly for isolated large hail.

SYNOPSIS

Large scale upper trough over W-Europe slides to the east. Surface air mass ahead of this trough is warm and moist, so expect widespread shower/thunderstorm activity.

DISCUSSION

A belt with widespread 9-10 g/kg ML mixing ratios runs from east Spain all the way to the Ukraine. Placed beneath 500hPa temperatures of -15°C and less, modest SBCAPE build-up is expected with a peak during the afternoon/early evening hours. Local moisture convergence or spots with higher surface dewpoints are embedded in this area, where SBCAPE may surpass 1000 J/kg, especially over parts of central/north Italy, W-Poland, Hungary and for sure over parts of central Ukraine, where SBCAPE locally reaches 2000 J/kg. Next to Poland, shear remains weak, so pulsating thunderstorms remain the main risk. We go ahead and cover parts of Ukraine with a level 1 due to locally excessive rainfall, as expected storm motion remains slow. Mainly during the more discrete phase, large hail could also accompany those storms, especially over Moldova and E-Romania. The same risk for areas further west, including Hungary and E-Slovakia.

A level 1 was also introduced for parts of Austria as conditions seem conducive for rapid storm clustering beneath a more diffluent high-level streamline pattern. Excessive rainfall may affect parts of central Austria, if this scenario verifies.

Another level 1 was issued for extreme E-Germany, W-Poland and N-Czech Republic. Initiation will be a mixture of forced convection along the cold front and more diurnal driven/orographically forced initiation in the warm sector over S-Saxony. Shower/thunderstorm coverage increases during the day in the highlighted area in a weakly capped air mass. This more negative fact for more isolated development may be offset by quite weak forcing, which moves in from the SW. Shear magnitude in the lowest 6km is adequate for organized multicell storms with large hail and strong wind gusts. Shear remains quite unidirectional throughout the forecast, but an isolated tornado is not beyond question, as enhanced LL moisture augments LL CAPE next to enhanced LL shear along the cold/warm front structures and potential deviant storm motion with stronger/long-lived storms. Latest thinking is that most organized storms may evolve over extreme E-Saxony and W-Poland due to good moisture support and adequate CAPE. After sunset, storms tend to weaken but activity may keep going well into the night over S-Poland.

Finally, a concentrated spot east of Denmark may see an isolated, organized thunderstorm throughout the daytime hours due to favorable CAPE/shear overlap. Isolated large hail may accompany that activity. Favorable thermodynamic/kinematic phasing becomes worse after sunset, so nothing severe is expected thereafter.