Bureau of Meteorology: Severe Weather Warning Education


Introduction

The table below details the criteria for issuing Severe Thunderstorm Warnings and Severe Weather Warnings.

The following link provides education resources on severe weather warning services.
Severe Thunderstorms Brochure


What are the criteria for issuing Severe Thunderstorm Warnings and Severe Weather Warnings?

A Severe Thunderstorm Warning is issued if the severe phenomena are directly caused by the thunderstorm.

Severe weather in a tropical cyclone will be covered by the Tropical Cyclone Warnings.


Phenomenon Severe Thunderstorm Warning Severe Weather Warning
Wind (Gusts) Gusts 90km/h or more Gusts 90km/h or more
Wind (Average)   Widespread winds over land of 63km/h or more
(Gale force)
Tornado All tornados  
Blizzard   Widespread blizzards in Alpine areas
Flash Flood (see note below) Heavy Rainfall that is conducive to flash flooding
or a reported flash flood
Heavy Rainfall that is conducive to flash flooding
or a reported flash flood
Large Hail Hail with diameter of at least 2cm (size of $2 coin)  
Storm Tide   Abnormally high tides caused by winds
(expected to exceed highest astronomical tide)
Large Waves   Unusually large surf waves expected to cause dangerous conditions on the coast (dependent on location - but generally surf exceeding 5m, less in the tropics).  Large surf is commonplace in SA, Vic and Tas, so warnings are only issued there for extreme events.  
What is a flash flood?

Intense rainfall can deposit a large amount of water over a small area in a small time period.  This water can cause localised flooding that can rise rapidly in a matter of minutes often catching people off-guard, which leads to a dangerous situation.  Torrents of water can wash people, cars and even buildings away at short notice.

Riverine flooding is generally the result of widespread rain, causing water over large areas to collect in streams and rivers, which overflow.  These floods generally rise at a slower rate and although quite devastating, do rise at a rate that usually allows for managed escape.  Riverine floods are still dangerous as flowing water can still wash people, cars, etc away.  Also, breaches of levees or other barriers may cause localised flash flooding as water flows through the breach into previously dry land.


Products

Severe Weather Warning
Severe Thunderstorm Warning
Superseded Warnings (Warnings replaced in the warnings restructure of 16 Nov 2004)
Graphical Severe Thunderstorm Products in NSW

Note that other specialised products are provided to key stakeholders - like emergency service organisations. These generally provide detailed technical information to assist these organisations in planning disaster mitigation strategies.


Return to Main Warnings Information Page


Last updated October 2004