Arrangements for Flood Warning Services in Victoria
February 2001

A4. Flood Warning Categories & Warning Definitions

A4.1 Flood Category Definitions

Current definitions are:

Minor Flooding. Causes inconvenience. Low lying areas next to watercourses are inundated requiring the removal of stock and equipment. Minor roads may be closed and low level bridges submerged.

Moderate Flooding. In addition to the above, may require the evacuation of some houses. Main traffic routes may be covered. The area of inundation is substantial in rural areas.

Major Flooding. In addition to the above, causes inundation of extensive rural areas and appreciable urban areas. Properties and towns are likely to be isolated and major traffic routes likely to be closed. Numerous evacuations may be required.

A4.2 Warning Definitions for Flood

Official notices for flooding come in three main types. These are either a Flood Advice, Flood Warning or notice of thunderstorms. The types are:

Flood Advice. Advice issued by the Bureau of Meteorology to media, agencies and the public. The message contains specific weather information and limited comment on potential flood impacts. The main purpose of the advice is to inform the public and agencies that a weather situation is developing which could result in flooding.

Flood Warning. Warning issued by the Bureau of Meteorology or Local Government (especially for flash flooding) to media, agencies and the public. The message usually contains details that flooding is about to occur or is happening, predictions, expected impact, and can include what actions should be taken. It also contains detail on when the warning was issued and when the next update can be expected. Other tailored information can also be included such as operation of weirs, lochs, comparison to historic events, contact numbers for information etc.

Some warnings issued by the Bureau of Meteorology are in consultation with water authorities where the authority's activities are inherently a part of the flood warning service. Melbourne Water prepares flood warnings for Greater Melbourne for issue through the Bureau.

A severe thunderstorm is defined as having one or more of the characteristics below:

  • Hail with diameter equal to or greater than 2 cm
  • Wind gusts equal to or greater than 90 km/hr (48kt)
  • Tornadoes
  • Heavy rain leading to flash flooding

In the case of thunderstorms which may cause flash or localised flooding the Bureau of Meteorology issues the following:

Severe Thunderstorm Advice. Advice valid for up to 6 hours, issued to the media and appropriate agencies whenever a severe thunderstorm has been identified or there are strong indications that severe thunderstorms will develop. A severe thunderstorm advice is used for weather based districts outside the Greater Melbourne area.

These districts are North Mallee, South Mallee, North Wimmera, South Wimmera, Lower North, Upper North, Lower Northeast, Upper Northeast, East Gippsland, West Gippsland, East Central, West Central, North Central, Western Plains, and West Coast.

Severe Thunderstorm Warning. Warning which covers the Greater Melbourne area and is valid for up to 2 hours. It is issued to the media and appropriate agencies whenever a severe thunderstorm has been observed in or close to the Metropolitan area (including Geelong), or when there is radar evidence for a severe thunderstorm or when there is significant evidence that severe storms are about to develop.

Significant Weather Chart. Chart issued routinely at 11:30 am during the convective season from October to April regardless of whether severe weather is expected or not. This chart is sent to emergency management agencies (VICSES, police, fire authorities), public utilities, and local and interstate Bureau of Meteorology offices.

It shows parts of the state where a watch is maintained for severe weather, and severe and non-severe thunderstorms. For other times of the year, this chart is only issued when severe weather is observed or expected.

Severe Thunderstorm Warning Chart. Chart issued showing the location and expected movement of severe thunderstorms with the Greater Melbourne area. This is issued to VICSES, Police, Melbourne Water and other utilities whenever a severe thunderstorm warning has been issued.

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