1. Development of a severe frontal rainband - plans for the Testbed- course study Jenni Teittinen Finnish Meteorological Institute 16 February 2007

2. A cold front moved over Finland on 26 August 2005 26 August 2005 12 UTC27 August 2005 00 UTC

3. Two rainbands developed 12.30 UTC 11.30 UTC 13.30 UTC14.30 UTC Pre-frontal Severe cold frontal

4. Nature caused emergency reports on 26 August 6 reported tornadoes

5. Lightning 26 August 2005 CG IC

6. Motivation Difficult to forecast – numerical models had high shear but no CAPE How could we forecast these type quite common events? Difficult to nowcast – we would anticipate severe weather in the first rainband Can the Testbed-observations explain why severe weather occured in the second rainband? The frontal rainband had line echo wave patterns –often observed with nonsupercell tornadoes Can we observe the nonsupercell tornado development with radar reflectivity and Doppler velocity? Can we observe a tornado vortex with the Kumpula polarimetric radar (differential reflectivity ZDR and cross-colleration coefficient)?

7. Why severe weather occured in the second rainband? Testbed-observations Soundings Wind profiler (LAP-3000) Weather transmitters

8. Can we observe the nonsupercell tornado development with radar reflectivity and Doppler velocity? Can we observe a tornado vortex with the Kumpula polarimetric radar (differential reflectivity ZDR and cross- colleration coefficient)? Lee and Wilhelmson 1997b Ryzhkov et al. 2005 Testbed data: Kumpula, Vantaa and Ikaalinen radars