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

Contact details: Mr Kevin Rae

S A Weather Service (SAWS)

kevin.rae@weathersa.co.za