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Interpreting Data

What do the different warning systems mean?

The website lists all current warnings issued by the Bureau of Meteorology. Warnings fall into a number of different categories. The first, and most common, type of warnings is the coastal wind warnings. These are issued by all states when winds are expected to exceed strong wind strength (25 knots). For winds averaging more than 25 knots and up to 33 knots, a strong wind warning will be issued. A gale warning is issued for winds averaging 33 knots and up to 47 knots. A storm warning is issued for winds averaging more than 47 knots. Note that gusts are generally up to 40% greater than the average wind.

The next type of warnings is the cyclone warning. A tropical cyclone watch is issued if a cyclone is expected to affect coastal communities within 48 hours, but not expected within 24 hours. The watch is upgraded to a tropical cyclone warning if a cyclone is expected to affect coastal communities within 24 hours, or is already affecting the communities. These warnings will provide details of the warning and watch areas, along with details about the cyclone?s intensity, location and movement. Extra information, such as expected intensification, flooding or storm surge forecasts, will also be provided in these warnings.

The next type of warnings is the winter weather warnings. These are most common in TAS, but are also occasionally issued in VIC, and in extreme cases NSW and SA. They include bushwalking alerts and sheep graziers warnings. They are issued when cold, wet and windy weather is expected, normally associated with strong frontal systems or deep low pressure systems during winter. They will often provide details of expected snowfall levels.

The next type of warnings is the severe weather warning. These warnings are provided when severe weather is expected that is not directly related to severe thunderstorms, tropical cyclones or bushfires. They may be issued for land gales, squalls, flash-flooding, dangerous surf or tides. They are issued when severe weather is expected to affect land-based communities within 6-24 hours. Examples of weather systems that may prompt severe weather warnings are ex-tropical cyclones, monsoon lows, east coast lows, strong cold fronts, strong pressure gradients, large ocean swells and local heavy rainfall events. They are usually updated every six hours while the weather system remains in place. They contain a list of the phenomena expected in the warning area, the threat area, a description of the weather pattern and a description of the threat.

The next type of warnings is the flood warnings. These are provided for most major rivers. A flood watch or advice is issued if flood producing rain is expected in the near future. This is upgraded to a flood warning if flooding is occurring or is expected to occur in a particular region. In areas where specialized warning systems are in place, warnings of minor, moderate or major flooding will be issued for specific river valleys and locations. These warnings will include predictions of the expected height of the river at towns along the river.

The next type of warnings is the fire weather warnings. These are issued when the fire danger rating is expected to be extreme over an area. In most states, these areas correspond to the Bureau of Meteorology forecast districts, but in NSW, they correspond to the Rural Fire Service Fire Areas. The fire weather warning will contain a description of the relevant meteorological conditions, the area affected and the time period of the warning. If a total fire ban has been issued by the local fire authority, this will also be included in the warning. These warnings are normally issued in the afternoon for the following day, but can be updated at any time.

The final major type of warning is the severe thunderstorm warning. These are issued when thunderstorms are expected to produce dangerous or damaging conditions. These conditions include wind gusts of 90km/h or more, tornadoes, heavy rainfall that is conducive to flash flooding or hail with diameter of at least 2cm. Detailed severe thunderstorm warnings are provided for densely populated cities and surrounding areas where radars are able to provide more information about storm structure and movement.

Broad-based severe thunderstorm warnings are issued for other parts of Australia, and these contain less detail. They will be issued every three hours however the detailed warnings may be issued every 30-60 minutes. The warnings will contain expected phenomena, threat area, time of issue, a broad description of the threat, detailed radar information including severe thunderstorm locations and expected paths, information on recent storm damage (if applicable), action statements and expected issue time for next warning.

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A hop, skip and jump for the Easter bunny to a chilly and wet Tassie

12:21 EST A series of cold fronts and a low pressure system will sweep over Tasmania during the next week, bringing showers on most days and keeping temperatures to those more likely to be experienced in winter.

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