Road Weather Alerts are issued for metropolitan areas (excluding Darwin), or state-wide in Tasmania, when weather elements or phenomena are expected to contribute to hazardous driving conditions.
Alerts are issued only when conditions are likely to be worse than normal for the season and location. For example, alerts for ice on roads are not normally issued for alpine districts in winter unless expected to be unusually severe or widespread.
Criteria for issuing Road Weather Alerts are if the following conditions exist and NO severe weather warning, severe thunderstorm warning or flood warning is in force:
a) Reduced visibility below 200 metres due to the presence of thick fog, dust, smoke, heavy or very heavy precipitation. Metropolitan areas only, excludes Tasmania.
b) Significant snowfall. Below 500 metres in Tasmania.
c) Snow or snow showers of moderate or heavy intensity from 12 hours before the warning start time, or during the warning validity period.
d) Flooding.
e) Predicted localised flash flooding due to heavy rainfalls or inundation from anomalously high tides.
f) Slippery roads due to rainfall after a prolonged dry spell of more than 4mm of accumulated precipitation, from 6 hours before the warning start time or during the warning validity period following a dry spell. A dry spell is defined as less
than a total of 4mm of precipitation accumulated from daily totals over 5 days, using only daily totals of more than 2mm or ice build-up on roads due to frost or freezing rain, in particular the occurrence of ‘black ice’ or where it is suspected
that water draining across roads may freeze.
g) Ice on roads. Defined by the presence of: (accumulated precipitation of greater than 2mm or PoP of greater than 25%) and temperature of less than +2 degrees) within 12 hours of the warning start time or during the warning validity period.
h) Hail (moderate to heavy precipitation with hail).
i) Average wind speeds of at least 65 km/h, or gusts of at least 90 km/h.
They are generally issued 12 to 18 hours prior to the onset of the hazardous conditions, updated 6 hourly thereafter until cancelled.
Road weather alerts, which are issued by each Australian State/Territory have been combined into a national product for Web Map Service and Web Feature Service layers.
