THE WA STORMSPOTTER

Welcome to the 2004 edition of the WA Stormspotter newsletter. We feature latest changes to the severe thunderstorm warning service, an article on the Borden supercell in January, the safety of using mobile and cordless phones in storms and a summary of severe weather in 2004. There have been many events, although no one event stands out as having a major impact on the community.  Tragically an SES volunteer died in a flash flood in the Karijini National Park in early April during the rescue of a tourist. This was another reminder of the dangers posed by thunderstorms. We thank all the spotters who sent us reports of severe storms in their area either by phone or by post. Even if you hear of severe thunderstorms in your general area we welcome that information as well.

Changes to the National Severe Thunderstorm Warning Service

On 16 November the Bureau of Meteorology implemented changes to its severe weather warning and severe thunderstorm warning services. In response to public confusion over the term advice, a single severe thunderstorm warning will be issued, replacing the two-tier severe thunderstorm advice and warning structure used in the past. The adoption of a national standard thunderstorm warning style means that that we have made some mostly cosmetic changes to our warning form - see example below.

This now allows for severe thunderstorm warnings to be issued for the entire state including the Kimberley and Pilbara. Warnings for the tropics, where provided, will be restricted to more long-lived lines of thunderstorms (squall lines) that are expected to produce damaging wind gusts at a major town such as Broome, Port Hedland or the Karratha/Dampier/Roebourne area, and can be identified by radar or by surface observations. As a result the expected lead-time will typically be less than two hours.

For more details see the web page at: www.bom.gov.au/announcements/swws.shtml

Sample Severe Thunderstorm Warning

TOP PRIORITY FOR IMMEDIATE BROADCAST

SEVERE THUNDERSTORM WARNING

for Damaging Winds

For people in the central South Coastal and adjacent Great Southern Districts.

Issued at 6:25 pm on Wednesday 15 December 2004

An area of thunderstorms has developed to the west and northwest of Esperance, moving in a southeasterly direction. Storms may be accompanied by very strong winds that could result in damage to property.

The FESA-State Emergency Service advises that people should be aware of thunderstorms. As storms approach secure loose items and move vehicles under cover. If lightning accompanies the storm disconnect non-essential electrical appliances and avoid using the phone. Stay indoors until the storms have passed. If you are caught outside seek shelter away from trees and metal structures. Driving conditions will be hazardous.

The next warning will be issued by 9:00 pm Wednesday.

The Borden Supercell Storm 29 January 2004

Overview

A severe storm caused strong winds that lifted roof tiles from several farmhouses, and hail as large as cricket balls (6-7 cm) near Borden north of Albany in the late afternoon. The features appear to be consistent with a supercell storm.

Damage Reports

Two storm spotters near Borden reported the event. Fred and Bronwen Gaze, 8 km north of Borden had strong winds thought to be easily 100 km/h that uprooted or snapped large trees and took the tiles of the roof of a few houses. There was little rain and no hail. Byron Bungey, 13 km southwest of Borden, experienced hail that began the size of golf-balls but for 5-10 seconds fell the size of cricket balls. However they were not rock hard but a 'bit soft'. Nevertheless vegetation was damaged, as was a car that was dented, but the windscreen was not broken. At the time Byron was harvesting a few kilometres to the northeast of the farmhouse and thought about 30mm fell in just five minutes with water about 7cm deep flowing through the paddock. A neighbour recorded 13mm in just three minutes. At Borden townsite, located between the two spotter reports, neither strong winds nor hail occurred. The damaging wind gusts on the northern side of the storm were from a southerly or southwesterly direction. This is consistent with winds associated with what is called the rear flank downdraft where strong winds descend from aloft at the back-end of the storm.

Radar

The Albany radar showed the storm developing northwest of Cranbrook at 03:40pm being steered by the prevailing mid-level northwesterly flow. After 4pm the storm appears to split and within half an hour the left moving cell deviates to the east-northeast. The radar showed heaviest rainfall occurred at about 5:40pm when the storm was near Borden (see image below). The storm probably lasted for about four hours.

Forecast Performance

A severe thunderstorm advice was first issued at 10 am for the Southern Coastal district, south and east parts of the Great Southern, and the Goldfields. This was updated regularly throughout the day. Reports of the severity were not received until well after the event.

Figure 1a. Splitting storm:  4:40pm.	Figure 1b. Storm moving NE near Borden at 5:40pm

Storm Safety: mobile and cordless phones

You've probably heard that telephones should not be used in storms because of the risk of electric shocks from lightning striking the telephone line and travelling along it. You may be wondering then if it's OK to use mobile or cordless phones. A report by Bondarenko & Associates (Surge Testing and Protection Consultants) December 2002, has found that it depends on where you are.

If you are outdoors, a mobile phone is much like any other metallic object such as an umbrella or a golf club. It is advised that such objects should not be carried outdoors in a thunderstorm, as they may attract a strike. So avoid using your mobile outside in a storm!

Indoors is a different matter. It is safe to use a mobile or cordless phone indoors provided all other recommended safety measures are observed: Don't stand near open doors or windows, and avoid touching metallic objects and electrical appliances, including the base station of a cordless phone. All of these are shock risks.

It has been found that using mobile and cordless phones is also safe in a car with a metallic roof, as long as it is stationary, and there are no electrical connections between the handset and the car. You should also wind up the windows and avoid touching any metallic parts of the car, whether you're using a phone or not. So in summary, a mobile or cordless phone is safe to use indoors or in a car, provided that all other safety precautions are followed, but outdoors it might act as a lightning rod, so don't use it!

Latest statistics on the Internet

The usage of the Bureau of Meteorology web pages continues to increase. In a recent survey in early December) the Bureau ranked 4th across all Australian sites visited by people within Australia (using "visits" as the ranking metric).

The top five rankings were:

Yes, the Bureau's web site was used more than the ninemsn site! This is quite amazing given ninemsn is normally set as the home page for Internet Explorer - the default server on most PCs sold today. One of the most popular pages on the web is weather radar. If you haven't tried it before have a look at:http://www.bom.gov.au/weather/radar/

All enquires regarding the Western Australian Storm Spotter Network can be directed to Joe Courtney, Kevin Smith or Andrew Burton on 08 9263 2222 or write to us: Severe Weather Section, Bureau of Meteorology, PO Box 1370, West Perth 6872.
E-mail address :- sevwx_wa@bom.gov.au

Severe Weather Summary January to December 2004