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SWFDP Bolepi House, Pretoria 02 November 2006 Kevin Rae (S A Weather Service)

Southern African Hail, Tornadoes and Heavy Rain:- Climatological Aspects. SWFDP Bolepi House, Pretoria 02 November 2006 Kevin Rae (S A Weather Service). T/C “BOLOETSE” 03 FEB 2006. T/C “ELINE” 22 FEB 2000. SEV T/S RGB 03 JAN 2005.

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SWFDP Bolepi House, Pretoria 02 November 2006 Kevin Rae (S A Weather Service)

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  1. Southern African Hail,Tornadoes and Heavy Rain:-Climatological Aspects SWFDP Bolepi House, Pretoria 02 November 2006 Kevin Rae (S A Weather Service)

  2. T/C “BOLOETSE” 03 FEB 2006 T/C “ELINE” 22 FEB 2000 SEV T/S RGB 03 JAN 2005

  3. Ave annual lightning NASA LIS (flashes.km-2.yr-1(1997- )

  4. What defines* a “Severe Thunderstorm”? • Large hail (19 mm diam.) • Strong surface wind gusts  50kts (92km/hr) • Tornado *NSSL definition

  5. CSIR Hail size (categories) CSIR / EMATEK Hail Research Project data (Gerhard Held) – used by kind permission Year: January 1984-1995 approx 12 years 12 365 Hail cards sent in by individuals 658 hail days

  6. A BASIC STRATIFICATION…. “Non-damaging” vs “Damaging” hail 79% 300 GRAPE HAIL DAYS PEA 150 WALNUT RICE 0 GOLF EGG++ EGG roughly a 4/5 : 1/5 split in terms of relative distribution…..

  7. A BASIC STRATIFICATION…. “Non-damaging” vs “Damaging” hail 79% 300 GRAPE HAIL DAYS PEA 150 WALNUT “damaging”: 21% RICE 0 GOLF EGG++ EGG roughly a 4/5 : 1/5 split in terms of relative distribution…..

  8. Hail by month : Seasonality( regardless of “hail size”) D J N M O F Hail Days (all cats) A S M A J J

  9. Relative frequency: Large/extreme hail (cat 4(walnut) to cat 7(egg++) NOV walnut, golf ball, egg,egg++ HAIL DAYS MAR golf ball, egg,egg++ egg, egg++ J F M A M J J A S O N D

  10. Tornadoes…9th Sept 2002 Mokopane F3

  11. 9th Sept 2002 Mokopane F3 N=100 normalised tornadoes,Log-linear world freq / distribution (Doswell+Brooks 2000)

  12. SA Tornadoes, 1905-1997 (Goliger 1997) < 200 recorded events 90% F2 or less, 8% F3

  13. Sounding-derived (N=60 000+) baseline climatology (USA), Craven, Brooks, Hart 10m/s threshold for discriminating F2 or greater tornadoes (0-1km shear)

  14. Goliger (CSIR): Gauteng tornadoes: 1905 onwards 56 tornadic events (1905-2000) 6 events, F3 or greater (11% of pop.) Approx every 10th event will cause “considerable damage” 17 November 2002: Tornado on N4 highway

  15. synth prox. Soundings within 3h and 185km of event NCEP T62 reanalysis (1948-2002 ; 50+ yrs) Craven, Brooks,Lee (2003) Atm. Research 67-68

  16. Contact details: MrKevin Rae S A Weather Service (SAWS) kevin.rae@weathersa.co.za

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