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Triggering of heavy snowfall in Frankfurt/Main as a possible result of urban effects J. Rapp

Triggering of heavy snowfall in Frankfurt/Main as a possible result of urban effects J. Rapp. City centre of Frankfurt on February, 24, 2005; Snow depth = 2- 7 cm (AP Photo/Wolfram Steinberg). Synoptic situation on Feb., 23, 2005, at 12 UTC. 13.00 UTC. Frankfurt City. 13.30 UTC.

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Triggering of heavy snowfall in Frankfurt/Main as a possible result of urban effects J. Rapp

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  1. Triggering of heavy snowfall in Frankfurt/Main as a possible result of urban effects J. Rapp EUMETCAL Course Langen 03.02.-06.02.2009

  2. City centre of Frankfurt on February, 24, 2005; Snow depth = 2- 7 cm (AP Photo/Wolfram Steinberg) EUMETCAL Course Langen 03.02.-06.02.2009

  3. Synoptic situation on Feb., 23, 2005, at 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  4. EUMETCAL Course Langen 03.02.-06.02.2009

  5. 13.00 UTC Frankfurt City EUMETCAL Course Langen 03.02.-06.02.2009

  6. 13.30 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  7. 14.00 UTC(1 h later) EUMETCAL Course Langen 03.02.-06.02.2009

  8. 14.30 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  9. 15.00 UTC(2 h later) EUMETCAL Course Langen 03.02.-06.02.2009

  10. 16.00 UTC(3 h later) EUMETCAL Course Langen 03.02.-06.02.2009

  11. 16.30 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  12. 17.00 UTC(4 h later) EUMETCAL Course Langen 03.02.-06.02.2009

  13. 17.30 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  14. 18.00 UTC(5 h later) 2nd maximum EUMETCAL Course Langen 03.02.-06.02.2009

  15. Possible reasons of changed (increased) precipitation in urban areas (Schütz, 1995): • Modification of cloud dynamics due to the effect of urban-enhanced precipitation (temperature effect) and urban surface roughness • Modification of cloud processes due to additional particle emission from different sources • Changed boundary layer processes due to droplet deflexion in the ground wind level depend on surface roughness EUMETCAL Course Langen 03.02.-06.02.2009

  16. Data Source: HLUG EUMETCAL Course Langen 03.02.-06.02.2009

  17. Temperature 500 hPa, Radiosonde data, 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  18. Vorticity 500 hPa, 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  19. Measured surface wind direction, 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  20. Radiosonde Idar-Oberstein (100 km SW of Frankfurt), 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  21. Radosonde Idar-Oberstein (100 km SW of Frankfurt), 18 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  22. Relative Humidity 700 hPa, 12 UTC EUMETCAL Course Langen 03.02.-06.02.2009

  23. Percentage of settlement and traffic (sealed) areas (in %) Data: Umweltatlas Hessen EUMETCAL Course Langen 03.02.-06.02.2009

  24. Summary: The heavy snowfall was not a result of an inversion temperature situation („industrial snow“). The snowfall was probably induced by artificial convection. The vertical temperature gradient exceed a threshold, which was necessary to trigger convection. But: Other/addtional causes cannot excluded. EUMETCAL Course Langen 03.02.-06.02.2009

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