1 / 18

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.

clark
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related