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Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss 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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2 Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland
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3 Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland
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4 Montreux, Lake Geneva, 18.7.2005 Source: Webcam Hotel Splendid, Montreux, Switzerland
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5 TRT (Thunderstorms Radar Tracking) TRT Cell tracking Montreux (webcam) TRT Cell-based VIL (Vertically Integrated Liquid) 18.7.2005 (12:50-14:35) 220 km 13dBZ 25dBZ 40dBZ 55dBZ
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6 TRT (Thunderstorms Radar Tracking) TRT Cell tracking TRT Cell-based VIL (Vertically Integrated Liquid) 18.7.2005 (12:50-14:35) 220 km 13dBZ 25dBZ 40dBZ 55dBZ
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7 TRT (Thunderstorms Radar Tracking) TRT Cell-based VIL (Vertically Integrated Liquid) 18.7.2005 (12:50-14:35) TRT Cell tracking 220 km 13dBZ 25dBZ 40dBZ 55dBZ
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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)
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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
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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
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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 km 2 8 people injured 15'000 cars damaged several vineyards destroyed Insured claims > €70 millions
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12 Hail swath on 18 July 2005 Hail crop damage claims (Swiss Hail Insurance)Daily maximum grid-VIL Daily maximum grid-VIL > 10 [kg/m 2 ] [kg/m 2 ] 0 204060 540 km Squares: communities where hail reported at least once
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13 Hail swath on 18 July 2005 Maximum grid-VIL > 5 [kg/m 2 ] (10:30-17:00 UTC) Hail crop damage locations (Swiss Hail Insurance) [kg/m 2 ] 0204060 100 km
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14 Hail swath on 18 July 2005 Maximum grid-VIL > 5 [kg/m 2 ] (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 [%] 20406080 100 0 100 km
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15 Hail swath on 18 July 2005 Maximum grid-VIL > 5 [kg/m 2 ] (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 [%] 20406080 100 0 [kg/m 2 ] 0204060 VIL POH
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16 18.7.2005: cell-based attributes Montreux (F2 tornado, 161 km/h) Geneva (F1 tornado)
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17 18.7.2005: max cell-VIL distribution
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18 Conclusions and outlook Reliable operational thunderstorms identification, tracking and 3D characterisation in 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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