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2010/07/12 1500 UTC
Gust 25+m/s Tor Hail 2+ cm
Helgoland, 2010/07/12 1330 UTC
Derecho-definition Major axis length: 400 km Fujita, T. T., and R. W. Wakimoto, 1981
Fig. SPC web site (Johns, Evans, and Corfidi)
Derecho climatology
Fig. SPC web site (Johns, Evans, and Corfidi)
Gatzen, C., 2004: A Derecho in Europe: Berlin, 10 July 2002. Wea. Forecasting, 19, 639–645
Punkka, A.-J., J. Teittinen, R. H. Johns, 2006: Synoptic and Mesoscale Analysis of a High-Latitude Derecho–Severe Thunderstorm Outbreak in Finland on 5 July 2002. Wea. Forecasting, 21, 752–763
López , J. M., 2007: A Mediterranean derecho: Catalonia (Spain), 17th August 2003. Atmos. Res., 83, 2-4, 272-283
Gatzen, C., T. Púčik, D. Ryva, 2011: Two cold-season derechoes in Europe. Atmos. Res., 100, 4, 740-748
Germany, 1997-2011: 10 new Derechoes, Average path 730 km Possibly 7 further events 106 Fatal, 200 INJ
Derecho hazards
• Outdoor activities • Traffic • Electrical outages • Large tree blow downs
Radar view
Reflectivity
Relative Velocity
Fig. Przybylinski, 2000
Conceptual model
Fig. Mahoney, Lackman, and Parker, 2009
Fig. Fujita, 1978
Cold pool
Increasing cold pool speed
Fig. Mahoney, Lackman, and Parker, 2009
PGA: Pressure gradient acceleration VAu’, VAv’: Vertical advection of perturbation wind VAū: Vertical advection of environmental flow
Idealized model studies
Fig. Weisman 1993
Rotunno, Klemp, Weisman, 1988 (RKW theory): Balance of cold pool and shear circulations
RKW and storm environments
Fig. Evans and Doswell, 2001
• RKW is not confirmed by proximity soundings
Observational studies Derecho environments are characterized by
• High low-level moisture (almost always) Johns and Hirt, 1987 Johns, Howard, and Maddox, 1990 Burke and Schultz, 2004 Coniglio, Stensrud, and Richman, 2004
• Steep lapse rates (often) Johns and Hirt, 1987 Johns, Howard, and Maddox, 1990 Cohen, Coniglio, S. F. Corfidi, and S. J. Corfidi, 2007
Observational studies Derecho environments are characterized by
• 250 hPa divergence (almost always) Johns and Hirt, 1987 Johns, Howard, and Maddox, 1990 Coniglio, Stensrud, and Richman, 2004
• Strongly-forced at 500 hPa (often) Evans and Doswell, 2001 Johns, Howard, and Maddox, 1990 Burke and Schultz, 2004
Observational studies Derecho environments are characterized by
• Strong low-level WAA (always) Johns and Hirt, 1987 Johns, Howard, and Maddox, 1990 Burke and Schultz, 2004 Coniglio, Stensrud, and Richman, 2004
• A strong low-level jet (almost always) Johns and Hirt, 1987 Johns, Howard, and Maddox, 1990
Example: 500 hPa flow and derecho path
Example: 500 hPa flow and derecho path
