EUMeTrain: Case Study on supercell: 9th June 2004

Summary

The case from 09 June 2004 is an exmaple of an unusual development of a super cell because it developed over the relative cool water of the North Sea and a second phase of intensifying occured about 4 hours after sunrise over Northern Germany. Precipitation amounts up to 20 mm and gusts up to Beaufort 10 were registered.

An intense frontal zone extended from England to Eastern Europe. The Southern parts of the North Sea and Norther Germany was affected by its warmer edge. Near the passage of the super cell the radiosoundings exhibited a strong vertical wind shear, potential instability between 1 and 5 km height and a tropopause at about 12 km with -64°C. The warm front was super-imposed by warm air advection and positive vorticity advection at the right entrance of a jet streak. That induced the development of a warm front wave. Within the potential unstable air during the evening of the 8th June a super cell developed near Scotland and moved after a temporary decaying and splitting till the morning of the 9th June to Hamburg. The right cell reached its maximum intensity around 07 UTC.

The surface pressure (amounts and tendencies) exhibited the typical dipole structure showing a meso cyclone in the frontal part of the super cell and a well-pronounced meso height at its rear. Tendencies of up to -5.6 hPa/3h and +3 hPa/3h were observed. Two times a V-Notch developed (between 02:00 and 02:30 UTC and around 07 UTC) with continuous overshootings and cloud top temperatures up to -69.5°C.

The NWP-fields were in a good correspondence to nearly all patterns. Only the GME-model decreased slightly the horizontal temperature gradient and the transition zone between stable and unstable air.