Perth 28-day rainfall forecast
Chance of rainfall somewhere within district
Issued 21 Sep 2017
The hemispheric long wave pattern has been relatively slow moving in recent weeks. There are four main troughs. Currently the most significant troughs are near the longitudes of South Africa, Western Australia, eastern Australia, and the south Pacific. Summary: Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 2 October to 6 October, 7 October to 11 October, and 13 October to 17 October. Rain events originating in the tropics and moving south are possible about 28 September to 2 October, 3 October to 7 October, and 14 October to 18 October. Over Western Australia the strongest cold fronts should occur about 24 September to 28 September, 8 October to 12 October, and 13 October to 17 October.
This forecast is produced by a multi-model ensemble consisting of dynamical atmospheric models, which are forced by the latest observed atmosphere, ocean, land and ice conditions. The models are designed to simulate features of the real atmosphere, including the daily movement of long and short wave patterns in the Southern Hemisphere.
The future probability of rain in each district is estimated using output from the multi-model ensemble, combined with historical information about the difference between the model forecasts and observed rainfall.
In this deterministic framework the skill of the forecast tends to decrease with time, however the forecasts are updated daily to provide the latest estimates of rainfall probability out to 28 days.