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Alessandro Hering 1 , Urs Germann 1 , Marco Boscacci 1 , Stéphane Sénési 2

Operational thunderstorm nowcasting in the Alpine region using 3D-radar severe weather parameters and lightning data. Alessandro Hering 1 , Urs Germann 1 , Marco Boscacci 1 , Stéphane Sénési 2 1 MeteoSwiss, Locarno-Monti, Switzerland 2 Météo-France, Toulouse, France.

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Alessandro Hering 1 , Urs Germann 1 , Marco Boscacci 1 , Stéphane Sénési 2

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  1. Operational thunderstorm nowcasting in the Alpine region using 3D-radar severe weather parameters and lightning data Alessandro Hering1, Urs Germann1, Marco Boscacci1, Stéphane Sénési2 1 MeteoSwiss, Locarno-Monti, Switzerland 2 Météo-France, Toulouse, France.

  2. Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland

  3. Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland

  4. Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland

  5. TRT (Thunderstorms Radar Tracking) 18.7.2005 (12:50-14:35) TRT Cell-based VIL (Vertically Integrated Liquid) TRT Cell tracking 220 km 40dBZ 25dBZ 55dBZ 13dBZ Montreux (webcam)

  6. TRT (Thunderstorms Radar Tracking) 18.7.2005 (12:50-14:35) TRT Cell-based VIL (Vertically Integrated Liquid) TRT Cell tracking 220 km 40dBZ 25dBZ 55dBZ 13dBZ

  7. TRT (Thunderstorms Radar Tracking) 18.7.2005 (12:50-14:35) TRT Cell-based VIL (Vertically Integrated Liquid) TRT Cell tracking 220 km 40dBZ 25dBZ 55dBZ 13dBZ

  8. Scan geometry, Orography • Scan geometry of Swiss radar La Dôle situated on a mountain top (1680 m a.s.l.) near Geneva • Orography roughly in the direction of the hail swath on 18 July 2005 Montreux (webcam)

  9. TRT (Thunderstorms Radar Tracking) • TRT: real-time object-oriented tool for thunderstorms nowcasting based on multiple-radar composites • 2003: TRT operational at MeteoSwiss • Detection: Dynamic reflectivity thresholding scheme • cells detected at individual thresholds: 36-48 dBZ • 2004: Improved cell position extrapolation • 2005: Lightning data added→multiple-sensors system • 2006: 3D multiple-radar derived storm properties cell-based (time series), grid-based (2D horizontal fields): • VIL (Vertically Integrated Liquid) • EchoTops 15/45 dBZ • Max storm reflectivity altitude

  10. Operational view: cell-based attributes VIL, 15/45 EchoTops, storm altitudes: • Cartesian composite 3 C-band Doppler radars • 20 elevation scan (-0.3° / 40°) • 12 CAPPI between 1 and 12 km • 5 min Lightning data: • CG positive/negative

  11. The severe hailstorm on 18 July 2005 • One cell, 11:00-15:00 UTC, developed to a supercell hailstorm moving over Lake Geneva to western Switzerland • 250 km track • hail swath 1200 km2 • 8 people injured • 15'000 cars damaged • several vineyards destroyed • Insured claims > €70 millions

  12. Hail swath on 18 July 2005 • Daily maximum grid-VIL > 10 [kg/m2] • Daily maximum grid-VIL • Hail crop damage claims (Swiss Hail Insurance) • Squares: communities where hail reported at least once 540 km [kg/m2] 20 40 60 0

  13. Hail swath on 18 July 2005 • Maximum grid-VIL > 5 [kg/m2] (10:30-17:00 UTC) • Hail crop damage locations (Swiss Hail Insurance) 100 km [kg/m2] 0 20 40 60

  14. Hail swath on 18 July 2005 • Maximum grid-VIL > 5 [kg/m2] (10:30-17:00 UTC) • Hail crop damage locations (Swiss Hail Insurance) • POH (Probability of Hail): Waldvogel et al. (1979) Hail: ΔH ≥ 1.4 km 3850 m 100 km [%] 100 0 20 40 60 80

  15. Hail swath on 18 July 2005 • Maximum grid-VIL > 5 [kg/m2] (10:30-17:00 UTC) • Hail crop damage locations (Swiss Hail Insurance) • POH (Probability of Hail): Waldvogel et al. (1979) Hail: ΔH ≥ 1.4 km 3850 m VIL POH 100 0 20 40 60 0 20 40 60 80 [kg/m2] [%]

  16. 18.7.2005: cell-based attributes Geneva (F1 tornado) Montreux (F2 tornado, 161 km/h)

  17. 18.7.2005: max cell-VIL distribution

  18. Conclusions and outlook • Reliable operationalthunderstorms identification, tracking and 3D characterisationin Alpine area needs: • high resolution in height / time: 20-elev. (-0.3° / 40°) in 5 min • dynamic reflectivity thresholding scheme: TRT • multiple-radar composites • Nowcasting in Alpine area: • use 3D storm attibutes VIL, 15/45 EchoTops, max storm refl. altitude, CG for assessing the severe weather potential of thunderstorms • combine grid-based 2D-animations and cell-based time trends • Outlook Alpine area: • VIL: determine typical values, thresholds for occurrence of hail • explore use of POH!? (Probability of Hail, Waldvogel et al.) • extend time series analysis to forecast thunderstorm development (stage in its life cycle)

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