Severe Thunderstorms

This information on Severe Thunderstorms in Australia is provided by the Bureau of Meteorology and Emergency Management Australia.

It is divided into seven sections:

1. THE IMPACT OF SEVERE THUNDERSTORMS
2. SEVERE THUNDERSTORMS: DEFINITION, CAUSES AND OCCURRENCE
3. SOME AUSTRALIAN SEVERE THUNDERSTORMS
4. THE WARNING SERVICE
5. ACCESS TO INFORMATION
6. PROTECTION FROM SEVERE THUNDERSTORMS
7. PROTECTION AGAINST LIGHTNING STRIKES

The most recent weather warnings around the country are available from the Weather & Flood Information page. Region-specific warnings are available from the regional pages. At the moment, there are

• Warnings current in:
• New South Wales / Australian Capital Territory,
• Victoria,
• Queensland,
• Western Australia,
• South Australia,
• Tasmania,
• Australian Capital Territory.

1. THE IMPACT OF SEVERE THUNDERSTORMS

Severe thunderstorms are localised events, usually affecting smaller areas than tropical cyclones and floods, so their devastating impact is often underestimated. These storms, which are more common than any other natural hazard, can occur anywhere in Australia. Each year, on average, severe thunderstorms are responsible for more damage (as measured by insurance costs) than tropical cyclones, earthquakes, floods or bushfires. Unfortunately, thunderstorms also kill people - between 5 and 10 deaths are caused by lightning strikes each year. More deaths occur when strong winds cause tree limbs to fall, debris to become projectiles and small boats in open water to capsize. Although many people believe that tornadoes do not occur in Australia, they have caused at least 41 deaths here.

2. SEVERE THUNDERSTORMS: DEFINITION, CAUSES AND OCCURRENCE

A severe thunderstorm is defined by the Bureau of Meteorology as one which produces:

• hail, diameter of 2 cm or more ($2 coin size); or
• wind gusts of 90 km/h or greater; or
• flash floods; or
• tornadoes, or any combination of these.

Most thunderstorms do not reach the level of intensity needed to produce these dangerous phenomena, but they all produce lightning which can cause death, injury and damage.

WHERE AND WHEN DO SEVERE THUNDERSTORMS STRIKE?
Severe thunderstorms can occur at any time of the year, although they are very rare during the dry winter months in the north. Most strike between September and March when the supply of solar energy is greatest, but severe winter storms linked to cold fronts are common in the south-west of Western Australia and south-east South Australia. The geographical spread of severe thunderstorms in Australia is difficult to determine because of our low population density and lack of observations over most of the continent. While records of thunderstorm impact show that the most damaging thunderstorms have occurred in the populous south-east quarter of the continent, analysis of wind, hail and tornado data suggests that severe thunderstorms are a significant threat throughout the country. The most damaging individual thunderstorms have hit south-eastern Queensland and the central NSW coast.

The Bureau of Meteorology is responsible for providing the Australian community with warnings of dangerous weather, in order to minimise damage and injury. A Severe Thunderstorm Warning is issued when a severe thunderstorm is reported, or there is strong evidence of a severe thunderstorm, and it is expected to persist. Severe thunderstorm warning services are provided from the Bureau's Regional Forecasting Centres in State and Territory capitals. Forecasters use computer model predictions, together with data from satellite pictures, radar displays, lightning detection networks, ground-based observations and reports from "storm spotters" to prepare the warnings. The radar displays are particularly helpful to thunderstorm forecasters by indicating where and how heavily rain is falling. Also, the Australian network of napproximately 3000 volunteer storm spotters provide valuable reports of severe weather to forecasters.

Severe storm warnings are immediately transmitted to radio and television stations, to authorities such as the police and emergency services, and to the Bureau's public access systems, which include recorded telephone services, Weather By Fax and the Internet.

• Warnings may be limited in accuracy because of the complexities involved in detecting thunderstorms, assessing their severity and predicting how they will move and evolve.
• Warnings may not provide much advance notice (maybe less than 15 minutes). Warnings are usually issued only after evidence of severe thunderstorms has been received. There can also be delays in communications systems and in getting the Warning broadcast by radio and TV.
• Severe thunderstorms should not be expected to occur everywhere in the warned area or for the entire period covered by the Warning.
• Warnings can only be effective if people take appropriate protective actions.
  

5. ACCESS TO INFORMATION

Severe thunderstorm warnings issued by the Bureau of Meteorology are accessible through the following communications systems:

1. Recorded Telephone - Dial 1900 926 113 (National Directory)
2. Weather By Fax - Free Fax 1800 630 100 (National Directory)
3. World Wide Web - http://www.bom.gov.au

Also, current weather radar displays, satellite pictures of the weather, weather charts and weather observations are available through the above Fax and World Wide Web services.

Apart from this brochure and other natural hazards brochures, Emergency Management Australia also publish free Severe Storm and Lightning Protection Action Guides, available through your State or Territory Emergency Service. Also visit the EMA Web site at www.ema.gov.au.

6. PROTECTION FROM SEVERE THUNDERSTORMS

Severe thunderstorms, including tornadoes and large hail, are our most frequent, damaging natural hazard, and can occur Australia-wide.

AT THE START OF THE STORM SEASON

• Trim trees and remove overhanging branches well clear of your home, and clear guttering and downpipes of leaves etc. (see photo 20).
• Check and secure tiles or roofing sheets.
• Protect skylights with strong wire mesh, and fit windows and glass doors with shutters or external metal insect screens (see photo 21).
• Clear your yard of loose materials and rubbish that may blow about, and be dangerous.

• Prepare an emergency kit of:
  • portable radio, torch, spare batteries;
  • first aid kit and manual, and strong plastic bags; and
  • plastic sheeting, timber strips, hammer and nails (for temporary repairs).
• List your emergency phone numbers.
• Check your home insurance is current and adequate.

• If you live in a caravan, ask your State or Territory Emergency Service for a 'Protecting Caravans' pamphlet.
• If you own a boat, check that it is securely moored, or protected on land.

WHEN A SEVERE THUNDERSTORM APPROACHES

• Listen to your local radio station for thunderstorm warnings.
• Shelter and secure pets and animals.
• Put garden furniture, toys, etc. inside. Fill garbage bins with water to hold them down.
• Park vehicles under solid shelter or cover with firmly tied tarpaulins/blankets.
• Secure all external doors and windows and draw curtains.
• Put valuables, medications and spare warm clothing in plastic bags with your emergency kit and keep handy.
• Disconnect all electrical items, external TV/radio aerials and computer modems.

WHEN THE STORM STRIKES

• Stay inside and shelter well clear of windows, doors and skylights.
• If the building starts to break up, shelter in the strongest part (cellar, internal room, hallway, or built-in wardrobe) under a mattress, doona, or a strong table or bench (see photo 22).
• Listen to your portable radio for storm updates.
• If outdoors, seek solid enclosed shelter (not a tree).
• If driving, stop, clear of trees, powerlines and streams. Don't use a fixed telephone during a thunderstorm due to lightning danger.

AFTER THE THUNDERSTORM PASSES

• Listen to your local radio station for official warnings and advice.
• Check for damaged windows, walls, or roof. Temporarily cover with plastic sheeting and nailed-on wooden strips.
• For emergency assistance, see below.
• If you don't need help, check, and if necessary, help your neighbours.
• Beware of fallen powerlines, damaged buildings and trees and flooded watercourses.
• Don't go sight-seeing.

EMERGENCY ASSISTANCE (Who and when to call)

• For emergency assistance with serious damage, or advice on temporary accommodation, food and clothing, call the State or Territory Emergency Service. (See directory page for all other emergencies (referred to inside front cover) or in state/territory government, or general pages. Note 24-hour emergency numbers if listed.)
• For power failure, fallen powerlines, electrical problems - call your local power supplier.
• For gas or water supply interruption or emergencies - call the relevant local supplier.
• To arrange permanent repairs to your home, call your insurance company for a claim form.

If unable to contact emergency services by phone:

• Continue to listen to the radio for official warnings and advice.
• Form a self-help group with family and neighbours.
• Watch for emergency service personnel who will be checking your area as soon as possible.

TAKE ACTION NOW

• Protect yourself and your family by following the advice in this pamphlet. Keep this information handy in a safe place which you can remember.
• Check your local electricity provider for advice on surge protectors and lightning conductors for homes (and other buildings) to help safeguard occupants and electrical equipment.

IF CAUGHT OUTDOORS

The distance (in kilometres) to a lightning flash may be estimated by dividing the time delay (in seconds) between the flash and the thunder by 3. If you hear thunder, find shelter urgently, especially if the time delay is less than 30 seconds. Try to remain sheltered for at least 30 minutes after the last sound of thunder.

• Seek shelter in a 'hard-top' (metal-bodied) vehicle or solid building but avoid small open structures or fabric tents.
• Never shelter under small groups of (or single) trees.
• If far from shelter, crouch (alone, feet together), preferably in a hollow. Remove metal objects from head/body. Don't lie down flat but avoid being the highest object in the vicinity.

• If your hair stands on end or you hear 'buzzing' from nearby rocks, fences, etc, move immediately. At night, a blue glow may show if an object is about to be struck (St Elmo's fire).
• Don't fly kites or model aeroplanes with control wires.
• Don't handle fishing rods, umbrellas or golf clubs etc.
• Stay away from metal poles, fences, clothes lines etc.
• Don't ride horses, bicycles or travel in open vehicles.

• If driving, slow down or park away from trees, power lines etc. Stay inside metal-bodied (hard top) vehicles or caravans but don't touch any metal sections.
• If swimming, surfing etc, leave the water immediately.
• If boating, go ashore to shelter as soon as possible.
• Be sure the mast and stays of a sailing boat are adequately 'grounded' to the water.

IF YOU ARE INDOORS

• Before the thunderstorm arrives, disconnect external aerial and power leads to radios and television sets. Disconnect computer modems and power leads.
• Draw all curtains and keep clear of windows, electrical appliances, pipes and other metal fixtures (eg don't use the bath, shower, handbasin or laundry/kitchen sinks).
• Avoid touching brick or concrete, or standing bare-footed on concrete or tiled floors.
• Avoid the use of fixed telephones. In emergencies, make calls brief.

FIRST AID

• Apply immediate heart massage and mouth-to-mouth resuscitation (CPR) to lightning victims until medical help arrives and they will have a good chance of survival. (You won't receive a shock from the victim.)

LIGHTNING FACTS

• When struck, people do not glow or 'fry to a crisp' but the heart and breathing are often affected.
• Only about 30% of people struck actually die, and the incidence of long-term disability is low, particularly when appropriate first aid is applied promptly.

• If your clothes are wet, you are less likely to be seriously injured if struck, as most of the charge will conduct through the wet clothes rather than your body.
• Average lightning bolts carry a current of 10,000 to 30,000 amps. An average radiator draws 10 amps.
• Lightning can, and often does, strike more than once in the same place.
• Worldwide, thunderstorms produce approximately 6,000 lightning strikes every minute!

This pamphlet was produced jointly by Emergency Management Australia and the Bureau of Meteorology.

Disaster Awareness Program 04/2000