Development of a severe frontal rainband

- plans for the Testbed-course study

Jenni TeittinenFinnish Meteorological Institute

16 February 2007

A cold front moved over Finland on 26 August 2005

26 August 2005 12 UTC 27 August 2005 00 UTC

Two rainbands developed

12.30 UTC11.30 UTC

13.30 UTC 14.30 UTC

Pre-frontalSevere cold frontal

Nature caused emergency reports on 26 August

6 reported tornadoes

Lightning 26 August 2005CG IC

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)?

Why severe weather occured in the second rainband?

• Testbed-observations

• Soundings

• Wind profiler (LAP-3000)

• Weather transmitters

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