Radar characteristics of a tornadic low topped mini-supercell in Finland

In the afternoon of 18 August 2004, a F1-tornado developed with a supercell in southern Finland only 20 km from the Anjalankoski Doppler radar. The parent storm started as a northeastward propagating multicell storm transforming into a supercell as an outflow boundary of a nearby storm reached the inflow area of the parent storm. The supercell turned to the right and had a distinct bounded weak echo region 40 minutes before the tornado formation. There was a pronounced hook echo before and during the tornado. The tornado was situated in the edge of the hook. The diameter of the storm defined by 15 dBZ reflectivity contour was 20 km and the visible cloud top generally below 8 km. While the echo top was initially above the strongest reflectivity gradient above the storm main core, it moved over the bounded weak echo region during the time of the tornado. The Doppler radar measured a tornado vortex signature with velocity differences of 30-38 m/s in storms mid and low levels before and during the tornado.