Severe Weather Warnings are provided for potentially hazardous or dangerous weather that is not solely related to severe thunderstorms, tropical cyclones or bushfires.
The Bureau of Meteorology issues Severe Weather Warnings whenever severe weather is occurring in an area or is expected to develop or move into an area. The warnings describe the area under threat and the expected hazards. Warnings are issued with varying lead-times, depending on the weather situation, and range from just an hour or two up to about 24 hours.
What weather conditions are Severe Weather Warnings issued for?
Severe Weather Warnings are issued for:
- Sustained winds of gale force (63 km/h) or more
- Wind gusts of 90 km/h or more (100 km/h or more in Tasmania)
- Very heavy rain that may lead to flash flooding
- Abnormally high tides (or storm tides) expected to exceed highest astronomical tide
- Unusually large surf waves expected to cause dangerous conditions on the coast
- Widespread blizzards in Alpine areas
Which warnings are issued when thunderstorms occur during other severe weather events?
Some severe weather events can be quite complex with thunderstorms occurring during a more widespread severe weather event (e.g. a band of heavy rain or vigorous cold front). In these circumstances Bureau's forecasters determine which warning(s) to issue to best inform the public about the hazards. This is done with consideration of warnings already in place and may involve consultation with local emergency services agencies. Users are advised to always consider all Bureau warnings issued in a severe weather event for their area.
What information is included in the Severe Weather Warning?
Severe Weather Warnings can contain the following information:
- Standard Emergency Warning Signal (SEWS) - sounded only for the most serious events
- List of severe weather phenomena expected in the warning area
- Threat area
- Warning issue time
- (Usually) Description of the weather pattern, including forecast developments of significant weather systems
- Description of the threat
- Action statements
- Advice of next issue time
Severe Weather Warning for Damaging Winds and Heavy Rainfall
An example of a text and map-based severe weather warning issued in South Australia.
How often is a Severe Weather Warning updated?
While the threat remains, a Severe Weather Warning will usually be updated every 6 hours (every 3 hours in South Australia), however more frequent warnings may be issued if required.
Limitations of severe weather warning service.
- Warnings services may be more limited for remote and unpopulated areas where data may not be available for effective monitoring and prediction
- Storm tide and dangerous surf warnings are only issued for limited parts of the coastline
Typical weather patterns that can cause severe weather
- Recently decayed tropical cyclones moving inland or into southern regions - sometimes interacting with cold fronts
- Monsoon lows producing widespread gales and/or rain in the tropics
- "East coast lows": Deep low pressure systems that can form in the Tasman Sea and affect the east coast of Australia
- Vigorous squally cold fronts
- Strong pressure gradients, often due to cold fronts, causing land gales - particularly in exposed alpine regions
- Distant tropical cyclones or deep southern low pressure systems producing ocean swells at Australian shores causing dangerous surf
- Locally intense rainfall that can cause flash flooding