What is a severe storm?

A severe thunderstorm (more common) or a land gale.

Causes of severe storm or gale

• Severe thunderstorm -- when warm, humid air near the ground receives an initial upward push from converging surface winds and rises rapidly in an unstable atmosphere.
• Land gale -- when there are large differences in atmospheric pressure, concentrated over a small distance. This can happen between a deep low and a strong high pressure system, or near an intense cold front.

Types of severe storm

• Severe thunderstorm (more common): produces hail, diameter of 2cm or more ($2 coin size), lightning, wind gusts of 90km/h or greater, or flash floods, or tornadoes or any combination of these.
• Land gale: gale force (62km/h) or stronger winds over the land. Usually last longer than severe thunderstorms and affect much larger areas than thunderstorms.

Likely impact of severe storm

Severe property damage and injury and death from falling or wind-borne objects.

Warnings: severe storm

• Storm warning services are provided by the Bureau of Meteorology as severe thunderstorm or severe wind advices.
• However, with lifetimes usually less than one hour and dimensions as little as 10km, severe thunderstorms are especially difficult to predict and monitor.
• Short-term warnings are usually released to the media up to one hour ahead.
• Longer-term advices are usually issued up to four hours ahead.
• For land gales, advices or warnings often cover periods of up to 12 hours.

Emergency action: severe storm

Before

* Check your home insurance: is it current and adequate?

* Trim trees and branches well clear of your home.

* Check and secure loose roofing.

* Clear guttering and downpipes.

* Fit windows with shutters or at least metal screens.

* Clear yard of loose materials that may blow about.

* Prepare an emergency kit of portable radio, torch, spare batteries; first-aid kit, manual and strong plastic bags; and plastic sheeting, timber strips, hammer and nails.

* List emergency telephone numbers: State Emergency Service, police, fire, ambulance, electricity, gas and water authorities.

When a severe storm approaches

* Listen to local radio for advices or warnings.

* Shelter and secure pets and animals.

* Put outdoor items, garden furniture and toys inside.

* Fill bins with water.

* Shelter vehicles or cover with tied tarpaulins or blankets.

* Secure doors and windows and draw curtains.

* Put valuables, medications, spare warm clothing in plastic bags with your emergency kit.

* Disconnect electrical items and outside TV radio aerials.

During

* Stay inside, shelter well clear of windows or skylights.

* If the building starts to break up, shelter in the strongest part (cellar, internal room, hallway, built-in robe) under a mattress, doona, or strong table or bench.

* 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.

After

* Listen to local radio for further warnings and advice.

* Check for damaged windows, walls, roof. Use plastic sheeting and nailed-on wooden strips to cover.

* Beware of fallen powerlines, damaged buildings and trees, and flooded watercourses.