Forecast Update
Valid: Fri 15 Aug 2008 18:00 to Sat 16 Aug 2008 06:00 UTC
Issued: Fri 15 Aug 2008 18:09
Forecaster: GROENEMEIJER

+ + + TORNADO OUTBREAK CURRENTLY UNDERWAY ACROSS SOUTHERN AND CENTRAL POLAND AND POSSIBLY SLOVAKIA EXPECTED TO CONTINUE THROUGH THE EVENING + + +

DISCUSSION



S and E Poland... Slovakia... E Czech Rep...

A line of supercells with reported tornadoes are ongoing across a line from just west of Warsaw to Krakow to Bratislava. These are expected to continue during the evening while moving eastward. As a southerly nocturnal low-level jet sets in across the Pannonian Plain and the Carpates, and the pressure gradient increases due to pressure falls east of the Alps, low-level shear profiles are expected to improve further. A continued threat of supercells producing (strong) tornadoes, very large hail and damaging winds is forecast. Storms may weaken no sooner than well after midnight.

E Austria... W and C Hungary

Strong storm-relative helicity of around 400 m2/s2 is expected to develop across extreme eastern Austria and the western half Hungary during the evening in reponse to pressure falls over Hungary. Storm that develop in this environment would have a high probability of producing tornadoes, also given the moist boundary layer that is present, with expceptionally high dew points of 23 C observed. The most important question is whether and if yes, how many storms will develop. Currently, we anticipate that isolated to scattered storms will develop, possibly clustering into a small MCS. An attendant threat of tornadoes, including strong tornadoes, as well as large hail and damaging gusts is forecast. Only after midnight should the boundary layer cool sufficiently to mitigate the severe threat.

Lithuania, N Belarus, Latvia

Given very strong low-level and deep-layer shear that should develop during the evening, clustering convective storms across Poland may develop into a bow echo. This system will likely move northeastward across the warm front and affect the southern Baltic States and N Belarus overnight, producing damaging wind gusts. Some threat of tornadoes will also exist with these storms and some large hail may occur as well.

Slovenia, Croatia, Bosnia and Herzegovnia, N Serbia

A few supercells will likely affect the area during the evening and into the night.Rather high LCL heights limit the threat of tornadoes, but large, possibly very large hail and damaging winds appear possible. That said, strong low-level shear and lowering LCL heights during the evening may suffice to produce conditions allowing for tornado development. Per GFS, the threat of convective storms should continue overnight.

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