Severe storms over Poland, Austria & Czech Republic

By Jochen Kerkmann, Gordon Bridge (EUMETSAT), Piotr Struzik (IMGW), Martin Setvak and Petr Novak (CHMI)

On 30 May, following the first hot spell of weather, a number of severe storms developed in Central Europe within a ridge of warm air that extended from northern Italy to Poland (maximum surface temperature up to 34°C). In Poland (near Krakow) three persons were killed by falling trees. There were 450 calls to the fire service during 30 May and the following night. In many cities and villages roofs were severely damaged or even blown away and close to Wroclaw electric train wires were damaged.

As a result, trains were delayed up to six hours. Trams in southern Wroclaw were completely brought to a halt due to fallen trees across the streets. In Krzyzowice four large high voltage electricity pylons were blown over. Many medium voltage transmission lines were partially damaged, especially in the regions of Olesnica and Sroda Slaska.

Figures 1 and 2 (and the corresponding animations) show the initial phase of the development, while Figures 4 ad 5 show the situation in the late afternoon. The first severe storms developed around 11:00–12:00 UTC over the Czech Republic, in the area north and south of Prague.

Both, the low cloud top temperatures of around -73°C and the small ice particles (indicated by the yellow colour in the RGB composite) indicate that the updrafts in these storms must have been very strong (see also Radiosounding Prague, 12:00 UTCsource: Deutscher Wetterdienst) with significant overshooting of the tops into the stratosphere. Of particular interest is the formation of several 'ring' structures within the cloud tops, most likely created by the building of a dome-like structure with a central area somewhat warmer than the edges.

This central warmer area could be the result of the highest part of the dome reaching thermal equilibrium with the surrounding, warmer stratospheric air after approximately 15–30 minutes. Examples of such a development can be clearly seen over Poland (between 14:15 and 17:15 UTC) and also over Austria (between 16:15 and 17:15 UTC).

The storm over Poland has all the appearances of a so-called supercell. A very unusual feature can be seen over this supercell at 17:15 UTC whereby a plume of cloud appears to emanate from the dome and streams away in a northerly direction. In the HRV image, because of the low elevation of the Sun at this time of the day, there is strong illumination on the western side of the plume and a clear shadow cast onto the dome to the east. Inspection of the NIR1.6 image indicates that the plume is comprised of small ice particles.

Additional content

Absolute Topography 300 hPa 12:00 UTC (source: Deutscher Wetterdienst)
Radiosounding Prague 12:00 UTC, (source: Deutscher Wetterdienst)
HRV image with lightning data 15:30 UTC, (source: IMGW, Krakow, Poland)