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Urban Effects on Heavy Snowfall in Frankfurt/Main: Analysis and Synoptic Comparison

Investigating urban effects triggering heavy snowfall in Frankfurt/M during a specific event. Analyzing the synoptic situation and possible reasons for increased precipitation in urban areas. Data sources include temperature, wind direction, vorticity, and relative humidity readings. Concludes that heavy snowfall was likely induced by artificial convection rather than an inversion temperature situation.

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Urban Effects on Heavy Snowfall in Frankfurt/Main: Analysis and Synoptic Comparison

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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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