swfdp bolepi house, pretoria 02 november 2006 kevin rae (s a weather service)
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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. - PowerPoint PPT PresentationTRANSCRIPT
Southern African Hail,Southern African Hail,Tornadoes and Heavy Tornadoes and Heavy Rain:-Rain:-
Climatological Aspects Climatological Aspects
SWFDP
Bolepi House, Pretoria
02 November 2006
Kevin Rae (S A Weather Service)
T/C “ELINE” 22 FEB 2000T/C “ELINE” 22 FEB 2000
SEV T/S RGB 03 JAN 2005SEV T/S RGB 03 JAN 2005
T/C “BOLOETSE” 03 FEB 2006T/C “BOLOETSE” 03 FEB 2006
Ave annual lightning NASAAve annual lightning NASA LIS (flashes.km LIS (flashes.km-2-2.yr.yr-1-1(1997- )(1997- )
What defines* a What defines* a “Severe Thunderstorm”?“Severe Thunderstorm”?
Large hail (19 mm diam.)
Strong surface wind gusts 50kts (92km/hr)
Tornado*NSSL definition*NSSL definition
CSIR Hail size (categories)CSIR Hail size (categories)
Category Diam(mm). Descrip.1 3 Rice2 6 Pea3 15 Grape4 25 Walnut5 35 Golf ball6 50 Hen's egg7 >50 "larger"
CSIR / EMATEK Hail Research Project data CSIR / EMATEK Hail Research Project data (Gerhard Held) – used by kind permission(Gerhard Held) – used by kind permission
Year: January 1984-1995 approx 12 yearsYear: January 1984-1995 approx 12 years
12 365 Hail cards sent in by individuals12 365 Hail cards sent in by individuals
658 hail days658 hail days
““Non-damaging” vs “Damaging” hailNon-damaging” vs “Damaging” hail
0
50
100
150
200
250
300
Hail days
cat1 cat2 cat3 cat4 cat5 cat6 cat7
Hail size (categories)
GAUTENG HAIL: 1984-1995
Series1
RICE
PEA
GRAPE
WALNUT
GOLFEGG
EGG++
roughly a 4/5 : 1/5 splitin terms of relative distribution…..
HAILDAYS
A BASIC STRATIFICATION….
00
150150
30030079%79%
““Non-damaging” vs “Damaging” hailNon-damaging” vs “Damaging” hail
0
50
100
150
200
250
300
Hail days
cat1 cat2 cat3 cat4 cat5 cat6 cat7
Hail size (categories)
GAUTENG HAIL: 1984-1995
Series1
RICE
PEA
GRAPE
WALNUT
GOLFEGG
EGG++
roughly a 4/5 : 1/5 splitin terms of relative distribution…..
HAILDAYS
A BASIC STRATIFICATION….
00
150150
30030079%79%
““damaging”: damaging”: 21%21%
Hail by month : SeasonalityHail by month : Seasonality( regardless of “hail size”)( regardless of “hail size”)
114
67
73
32
1611
710
21
70
104
132
0
20
40
60
80
100
120
140
Month
HAIL DAYS : 1984-1995
Haildays
Haildays 114 67 73 32 16 11 7 10 21 70 104 132
1 2 3 4 5 6 7 8 9 10 11 12
HailDays(all cats)
J
J J
A
A
FM
M S
O
N
D
Relative frequency: Large/extreme Relative frequency: Large/extreme hail (cat 4(walnut) to cat 7(egg++)hail (cat 4(walnut) to cat 7(egg++)
0
10
20
30
40
50
60
Hail days
1 2 3 4 5 6 7 8 9 10 11 12
Month
Extreme events (4+)
sev(4 to 7)
sev(5 to 7)
sev(6+7)
HAILDAYS
egg, egg++
golf ball,egg,egg++
walnut, golf ball,egg,egg++
NOV
MAR
J F M A M J J A S O N DJ F M A M J J A S O N D
Tornadoes…Tornadoes…
99thth Sept 2002 Sept 2002 Mokopane F3 Mokopane F3
99thth Sept 2002 Mokopane F3 Sept 2002 Mokopane F3
N=100 normalised tornadoes,Log-linear world N=100 normalised tornadoes,Log-linear world freq / distribution (Doswell+Brooks 2000)freq / distribution (Doswell+Brooks 2000)
SA SA Tornadoes,Tornadoes,
1905-19971905-1997
(Goliger (Goliger 1997)1997)
< 200 < 200 recorded recorded eventsevents
90% F2 or 90% F2 or less,less,
8% F38% F3
Sounding-derived (N=60 000+) baseline Sounding-derived (N=60 000+) baseline climatology (USA), Craven, Brooks, Hartclimatology (USA), Craven, Brooks, Hart
10m/s threshold for discriminating F2 or 10m/s threshold for discriminating F2 or greater tornadoes (0-1km shear)greater tornadoes (0-1km shear)
17 November 2002: Tornado on N4 highway
Goliger (CSIR):Goliger (CSIR):Gauteng tornadoes: 1905 onwardsGauteng tornadoes: 1905 onwards
56 tornadic events (1905-2000)56 tornadic events (1905-2000)6 events, F3 or greater (11% of pop.)6 events, F3 or greater (11% of pop.)
Approx every 10th event will causeApprox every 10th event will cause““considerable damage”considerable damage”
Craven, Craven, Brooks,Lee Brooks,Lee
(2003)(2003)Atm. ResearchAtm. Research
67-6867-68
NCEP T62 reanalysis NCEP T62 reanalysis (1948-2002 ; 50+ yrs)(1948-2002 ; 50+ yrs)
synth prox. synth prox. Soundings within 3h Soundings within 3h and 185km of eventand 185km of event