THE WA STORMSPOTTER
Produced by the WA Severe Weather Section Vol 10 No 1.
03 April 2008
Welcome to the 2008 edition of the WA Stormspotter newsletter. There
have already been a couple of significant events affecting Western Australia
in 2008. In this edition we feature the supercell thunderstorms north
of Geraldton on 18 March, 2008, the 88 knot gust recorded at Roebourne
Aerodrome on 8 March, 2008, and the tornado reported near Maya on 16 December,
2007.
There are currently 308 registered WA storm spotters. We thank all the
spotters who sent us reports of severe thunderstorms in their area either
by phone, post or via the web. Even if you hear of severe thunderstorms
in your area we welcome that information as well. We are keen to recruit
new storm spotters in coastal areas between Rockingham and Albany for
severe cool season storms.
Cool Season Tornadoes
With the winter months approaching we would like to remind our storm
spotters to be vigilant of the risk of cool season tornadoes. A tornado
is a column of air that is rapidly rotating. It can be in contact with
the ground, either pendant from a cumuliform cloud or underneath a cumuliform
cloud, and often (but not always) visible as a funnel cloud.
Tornadoes, particularly cool season tornadoes, have become a popular
topic amongst the media and public in recently. On average there are 6
tornado events each year over an area mainly southwest from Lancelin to
Albany. In the 2007 cool season five tornadoes were reported. Cool season
tornadoes are fast moving, last only a short time and have very localised
effects. They are often associated with cold fronts but do not necessarily
occur on the leading edge of the front; they may occur ahead of or behind
the front. Significant tornadoes in the past include; 22 September 1993
in Mandurah, 25 August 1999 in Fremantle, 17 October 2003 when several
tornadoes were reported through the southwest of Western Australia, 11
August 2004 in Bunbury, 16 May 2005 in Bicton and Bunbury and 23 July
2007 in Rockingham.
National Storm Spotters Website
Since July 2005, the Bureau of Meteorology has been running the National
Storm Spotters Website: www.bom.gov.au/storm_spotters/index.shtml
The website contains a wealth of information including: Duties of storm
spotters, what storm spotters report, how to join the storm spotters network
and storm spotter links. The links section includes the storm spotter's
handbook, spotter safety information, national warnings page and significant
weather summaries. The links section also includes report forms and the
storm spotter's newsletters, both of which will require a user id and
password for access.
All enquires regarding the Western Australian Storm Spotter Network can
be directed to Joe Courtney, Brad Santos or Andrew Burton on 08 9263 2222
or 1800 802 135 (free call) or write to us: Severe Weather Section, Bureau
of Meteorology, PO Box 1370, West Perth 6872.
E-mail address: - sevwx_wa@bom.gov.au
Geraldton Supercells, 18 March 2008
Overview
Geraldton radar showed a supercell to the north of Geraldton which split
into a left and right moving supercell at 1520 WDT. The left mover moved
east southeast and lasted till 2000 WDT and the right mover moved south
and lasted till 1820 WDT.
Damage Reports
A storm spotter located south of Dartmoor reported a swathe of damage
13km long and 1km wide in a west to east direction. Sheds were demolished
and there was significant tree damage, with lots of water still over the
area the next day.
Observations
The storm spotter reported 80mm of rain in 30 minutes, which has an average
recurrence interval of over 100 year for this location. Hail of 2 centimetres
in diameter was also reported. There was no report of a funnel cloud or
tornado but fast moving low cloud was observed.
Although forecasters were able to identify the storm as being potentially
severe by the radar signature, without the spotter's report there was
no way to know if the storm actually produced severe weather on the ground.
Figure 1. Geraldton radar scan at 1620 WDT, showing the right moving
supercell near Horrocks moving south and the left moving supercell near
Binnu moving east southeast towards Dartmoor.
Roebourne Thunderstorm, 8 March 2008
Roebourne Aerodrome reported a gust of 163km/h at 1911 WDT, which was
the third highest non-cyclonic gust recorded in Western Australia. The
highest non-cyclonic gust ever recorded in Western Australia was 193km/h
at Forrest on 20 November 1959, followed by 172km/h at Warburton on 14
November 2005. Damage reports have been limited to one caravan in Roebourne
Wind, Temperature and Rainfall
Storm force mean winds (above 90km/h) were recorded between 1920 and
1930 WDT and winds greater than gale force (63km/h) were recorded between
1920 and 1950 WDT. 30.4mm of rain was reported in the 24hrs to 9am 9 March
at Roebourne, with the aerodrome reporting 24.0mm in the same period,
with 10.0mm falling in the ten minutes to 1950 WDT. The temperature fell
9.3șC in ten minutes from 34.9șC to 25.6șC, while the lowest temperature
recorded during the event was 19.2șC.
Synoptic Situation
At 3pm WDT 8 March, a surface trough was located through inland parts
of the Pilbara. A low pressure system was located in the trough to the
southeast of Roebourne. The thunderstorm was most likely initiated from
convergence between the northwest sea breeze and easterlies over land.
Figure 2 - Port Hedland radar scan at 1900WDT
Maya Tornado, 16 December 2007
A keen spotter photographed a tornado near Maya, north of Dalwallinu,
around 1600 WDT. It had a width of about 300m and it travelled a distance
of 4km in about 15 minutes. Geraldton and Perth radar showed a left moving
supercell which formed just inland of Jurien Bay around 1400 WDT and tracked
east.
Figures 3 and 4 - picture of the tornado near Maya (left) and
Geraldton radar scan at 1610 WDT.
Severe Weather Summary 2007- March 2008
|
Date
|
Description
|
|
4-5 January
|
Moisture associated with a tropical low interacted
with a deep trough resulting in heavy rain across the Goldfields,
Eucla and South Coastal districts. Two bridges were washed away and
approximately 50000 sheep died from hypothermia and drowning. Stokes
Inlet recorded 180mm in the 24hr to 9am on the 5th, with Esperance
Aero recording 177mm (226mm/48hours) and Munglinup West 161.4mm. Esperance
also recorded 111km/h wind gusts. |
| 23 January |
Norseman reported a gust of 104km/h from a
dry microburst. |
| 28 January |
Thunderstorms enhanced strong easterlies and
caused minor property damage around Ballajura and Malaga, with a house
partly unroofed in Karragullen. |
| 3 February |
High temperatures (Hyden max. temp. 48.6C)
and strong dry northerly winds caused extreme fire weather conditions
across the SWLD. A total of 16 houses were destroyed by fire in Dwellingup. |
| 19 February |
A thunderstorm produced a gust of 106km/h
at Kununurra. |
| 22 February |
Thunderstorms produced a gust
of 93km/h at Mt Magnet Airport and a right moving supercell was observed
on the Esperance radar to the west northwest of Salmon Gums. |
| 24 February |
A supercell thunderstorm developed southeast
of Dalwallinu and produced 69mm at Mouroubra and 61mm at Bimbijy in
the Central Wheatbelt. |
| 26 February |
Lightning strikes cut power to 25000 properties
in Perth, with Perth Airport recording 551 lightning strikes in the
24hrs to 9am. There were reports of hail and localised flooding in
the southern suburbs. Two left moving supercells were identified on
the Perth radar in the Central Wheatbelt. |
| 1 March |
The passage of a cold front produced
a gust of 102km/h at Cape Leeuwin and 91km/h at Busselton Jetty. |
| 4-5 March |
A squall line moved along the
Pilbara coast and produced gusts of 91km/h at Port Headland Airport,
102km/h at Karratha Airport, 102km/h at Mardie and 126km/h at Varanus
Island. |
| 7 March |
A thunderstorm produced a gust
of 96km/h at Varanus Island. |
| 16 March |
A thunderstorm produced a gust
of 102km/h at Paraburdoo Airport. |
| 15 April |
The passage of a cloud band and
cold front produced 73mm at Karnet, 69mm at Dwellingup and 68mm at
Mount William. Dwellingup recorded 36mm in 1 hour which has a 1 in
20 year return period. |
| 29-30 April |
A cold front produced a wind gust
of 100km/h at Cape Leeuwin and 94km/h at Busselton Jetty on the 29th
and a wind gust of 106km/h at Cape Leeuwin and 93km/h at Rottnest
Island on the 30th. |
| 26 May |
There was minor damage (fences
demolished) associated with a weak tornado in Ocean Reef. |
| 27 May |
A cold front produced a wind gust
of 91km/h at Cape Naturaliste. |
| 22-23 June |
A cold front produced gusts of
113km/h at Rottnest Island on the 22nd and 107km/h at Cape Leeuwin
on the 23rd. |
| 27 June |
A cold front produced a gust of
102km/h at Rottnest Island. |
| 29 June |
The passage of a cold front produced
a gust of 98km/h at Cape Leeuwin. |
| 1-3 July |
A strong front on 1 July was followed
by a further strong westerlies on the 2nd and 3rd. There was moderate
damage in South Perth, a reported tornado near Gnowangerup (1st) and
golf-ball sized hail at Brunswick Junction on the 2nd. |
| 22 July |
A house at Port Kennedy lost one-third
of its roof during a cold front. No other damage was reported. |
| 23 July |
The passage of a cold front around
7pm produced a tornado that caused a narrow swathe of damage through
Rockingham about 50m wide and 2.5km in length, with around 70 houses
sustaining damage. The damage seemed consistent with an F1 tornado
(winds of 118-178km/h). |
| 30-31 July |
The passage of a cold front resulted
in gusts of 109km/h at Cape Leeuwin, 102km/h at Rottnest Island and
96km/h at Cape Naturaliste. |
| 1 August |
The passage of a cold front produced
gusts of 102km/h at Cape Leeuwin and 96km/h at Cape Naturaliste. |
| 6 August |
A cold front produced gusts of
113km/h at Noresman Airport and 96km/h at Esperance Aerodrome, with
small hail reported in the Perth Metropolitan area. |
| 22 August |
The passage of a cold front produced
a gust of 93km/h at Cape Leeuwin. |
| 26 August |
A cold front produced gusts of
122km/h at Cape Leeuwin, 106km/h at Rottnest Island, 104km/h at Cape
Naturaliste, 102km/h at Busselton Jetty and 94km/h at Bunbury. |
| 29 August |
Rottnest Island recorded a gust
of 94km/h in the post frontal cold pool. |
| 4 September |
The passage of a cold front produced
gusts of 100km/h at Cape Leeuwin and 91km/h at Jacup. |
| 12 September |
A weak tornado passed through
Perth's western suburbs in a pre-frontal line of showers, with only
minor damage reported. Strong gusts included: 109km/h at Cape Leeuwin;
106km/h at Cape Naturaliste and Norseman. |
| 14 September |
The passage of a cold front produced
gusts to 108km/h at Cape Naturaliste and 99km/h at Busselton Jetty.
|
| 15 September |
A strong westerly air stream produced
a gust of 102km/h at Cape Leeuwin. |
| 18 September |
A strong westerly air stream produced
a gust of 100km/h at Cape Leeuwin. |
| 17 October |
The passage of a cold front produced
gusts of 93km/h at Cape Leeuwin and 91km/h at Esperance Airport. |
| 26-27 October |
The passage of a series of cold
fronts followed by a cold pool of air produced severe gusts across
the SWLD and Eucla, with the highest of these being 100km/h at Rottnest
Island. Scattered minor damage was reported in Perth. |
| 2 November |
Wyndham recorded a gust of 94km/h
during a thunderstorm. |
| 14 November |
A thunderstorm produced a gust
of 135km/h in Wyndham with 12.6mm of rain falling in 10 minutes. |
| 18 November |
Forrest recorded a gust of 94km/h
during a thunderstorm. |
| 23 November |
A thunderstorm produced a gust
of 91km/h at Kununurra Airport. |
| 30 November |
Kununurra recorded a gust of 94km/h
in a thunderstorm and Cape Leeuwin recorded 93km/h during a cold front. |
| 11 December |
A severe thunderstorm at Boolardy
Station caused large hail, 44mm of rain in half an hour and strong
winds. Sheds were damaged, trees were knocked down and abut 1000 goats
perished. |
| 16 December |
Maya tornado, see report. Thunderstorm
activity in the Central Wheatbelt also produced heavy rainfall with
Nambung Station recording 112mm, Kokardine recording 102.6mm and Wongan
Hills RS recording 62mm. |
| 17 December |
Norseman Airport recorded 16.4mm
in 10 minutes during a severe thunderstorm. |
| 30 December |
Extreme fire weather conditions
fanned an ongoing fire in the Boorabbin Nature Reserve, and three
people died when their trucks were caught in the fire on the Great
Eastern Highway. |
| 8 January |
Hail to 3cm at Mount Barker caused
some minor damage at 1510 WDT. Gusts of 91 km/h were recorded at Mount
Magnet at 2148 WDT and Lake Grace at 1757 WDT. |
| 13 January |
A squall line produced gusts to
113 km/h at Argyle Aerodrome at 1838 WDT. Fitzroy Crossing Airport
reported 46.8mm in 34 minutes to 1454 UTC (2354 WDT). |
| 2 February |
A storm spotter near Hyden reported
golf ball size hail at 9:30pm.Newman recorded a gust of 94 km/h at
1542WDT. |
| 4 March |
Learmonth Airport reported a wind
gust of 58 knots (107 km/h) at 1616 WDT |
| 8 March |
Roebourne Aerodrome reported a
wind gust of 88 knots (163 km/h) at 1911 WDT |
| 18 March |
A stormspotter located south of
Dartmoor (north of Geraldton) reported 80mm in 30 minutes, 2cm diameter
hail and a narrow swathe of damage from the left mover. Geraldton
radar showed a supercell that split into two severe cells. |
| 31 March |
Ex-TC Pancho caused strong winds
and duststorms in the wheatbelt, heavy rain through southern and central
parts of the SWLD - some flooding at Northam (22mm in 19 minutes). |
What to Report - a reminder
Spotters are asked to report to the WA Bureau of Meteorology if they
observe:
- Hail 2 cm diameter ($2.00 coin size) or larger
- Damaging winds (90 km/h) or greater (e.g.. trees snapped, uprooted,
large branches down; roofing tiles / iron lifted; structural damage
to well constructed buildings)
- Tornadoes (rotating funnel-shaped clouds extending to or near ground
level)
- Very heavy rainfall (unusually heavy rainfall, or rainfall resulting
in localised flash flooding)
As soon as it is safe, phone your report to our "freecall"
number: 1800 802135 or complete the online report form at http://www.bom.gov.au/storm_spotters/
Note: Safety is always more important than reporting
and the Bureau does not authorise and will not be liable for the consequences
of your taking risks to your safety when performing any of your tasks.
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