Derechos in Central Europe

Christoph Gatzen1

1European Storm Forecast Experiment, gatzen@estofex.org

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