EUMeTrain: Summer convection over Central Europe, 27 July 2006

Authors

LCRS
Thomas Lotz
André Obregón

DWD
Wilfried Jacobs

Introduction

Thunderstorms belong to the short-living weather phenomena. Due to their associated risks caused by lightnings, heavy rainfall or hail they are of great interest for the customers. A precise forecast of summer convection is therefore one of the most important tasks for forecasters. Remote sensing data combined with synoptic information give the opportunity to monitor the relevant developments, especially for nowcasting (forecast for the next few hours).
On 27 July 2006 such short-living-convective cells developed over Germany. These convective events marked the end of a long lasting heat period which characterized July 2006. Reports about thunderstorms and heavy local rainfalls were issued. Heavy rainfall flooded streets and cellars, lightning damaged houses and trees were uprooted by heavy gusts. A huge crane was blown over and crashed into the Neckar river.

Beginning of thunderstorm near Stuttgart on 27 July 2006
(Photo by Moritz von Hacht: www.wetter-foto.de)

Meteosat-8 RGB HRV/HRV/IR10.8: 27 July 2006: 15 UTC.	Meteosat-8 IR10.8 Enhanced: 27 July 2006: 15 UTC.

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This case study deals with different parameters describing the preconditions and development stages of convective processes. There are some typical phenomena in association with summer convection occurring during this day:

• Development of multi and super cells
• Cell splitting or "severe right moving"
• Development of a squall line
• Surface pressure with a dipole structure connected to severe convection

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Parameters used in this case study:

• Satellite imagery:
• IR10.8 Enhanced
• WV6.2


• RGB Composites:
• Convective Storms RGB
• Airmass RGB
• High Resolution Visible RGB


• Basic Synoptic Parameters:
• Weather charts
• Surface pressure tendencies
• Geopotential height 300 hPa
• Pseudopotential temperature and wind
• Maximum wind speeds during the last hour
• Surface observations
• Lightning observations during the last half hour


• Radar:
• DWD PI (international composite)


• NWP Parameters:
• IPV 310 K
• Vertical Motion 500 hPa
• Thermal Front Parameter + Relative Topography
• Temperature Advection 700 hPa


• Soundings (field distribution):
• Nakamura Gusts
• Precipitable Water
• KO-Index


• Station Bergen (northern Germany):
• Detailed Investigations


• Nowcasting-SAF-product "Lifted index":
• Interpretation
• Limitations



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Preconditions likely for thunderstorms:
• Potential instability
• Upward motion
When upward motion occurs severe convection can start in an potentially unstable airmass. A potentially unstable airmass is normally characterized by relatively warm and moist air in lower levels of the atmosphere and relatively cold and dry air aloft.


Initiating mechanisms for convection:

• Diabatic heating through insolation (free convection).
• Warm air advection in lower levels and cold air advection in upper levels yielding increased vertical temperature gradient
• Orographic induced upward motion (forced convection)
• Upward motion due to synoptic forcings (e.g., leading edge of a trough, convergence near surface).

The preconditions for convection are discussed and investigated by several basic meteorological parameters and derived model parameters in relation to Meteosat-8 images. Radar data and lightning detection are used additionally due to their importance for summer convection diagnostics.


Following conceptual models are considered:

• Squall line (cloud patterns, surface pressure tendencies, position of radar reflectivity and lightning detections in relation to cloud tops)
• Convective cloud features at the leading edge of frontal cloud bands (see Manual of Synoptic Satellite Meteorology)
• Enhancement of convection by PV (in relation to dark stripes) (see Manual of Synoptic Satellite Meteorology)

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LCRS - Laboratory for Climatology and Remote Sensing
Faculty of Geography, University of Marburg
Germany