Forecast Update
Valid: Sat 18 Jul 2009 14:00 to Sun 19 Jul 2009 06:00 UTC
Issued: Sat 18 Jul 2009 14:50
Forecaster: GROENEMEIJER

A level 2 was issued for parts of Poland, mainly for excessive rainfall, tornadoes, severe winds, and to a lesser extent for large hail.

A level 1 was issued for Hungary, parts of Slovakia, much of Poland, SE Sweden and much of the NW and central Balkans mainly for large hail, and to a lesser extent for severe wind gusts and excessive precipitation.

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

SYNOPSIS

Please refer to the Storm Forecast.

DISCUSSION

Poland...

A deepening frontal wave over the Czech/Slovak border region is expected to intensify as it moves northward during the day. Covnective initiation is now underway across Poland, and most fo the storms develop along a convergence line near a line from Gdansk to Katowice. It is expected that the slow will become highly helical ahead of the northward movin wave cyclone. Strong warm air advection within an air-mass should lead to the development of one or more intense MCS'es this evening, with the potential to produce extreme rainfall amounts. Moreover the helicity of the flow with 0-3 SRH values of 400-500 m2/s2 forecast, indicates that a threat of tornadoes will be present during the evening hours, as well as severe winds and large hail. For the area most at risk, a level 2 seemed necessary.

SE Sweden...

The level 1 area has been expanded to include parts of southeastern Sweden. Storms currently present in the area develop in an environement with >15 m/s 0-3 km shear, which may support updraught rotation and hence an increased large hail threat. After these storms weaken during the evening, remains of convective acitivity developign across Poland may also produce wind and very heavy rain during the morning hours. The combined risk marginalyl warrants a level 1 for this area.