Perth 28-day rainfall forecast
Chance of rainfall somewhere within district
Issued 27 May 2017
The hemispheric long wave pattern has remained stable in recent weeks. There are five main troughs. Currently the most significant troughs are near the longitudes of South Africa, the Indian Ocean, eastern Australia, the southeast Pacific, and the Atlantic Ocean. Summary: Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 30 May to 3 June, 17 June to 21 June, and 25 June to 29 June. Rain events originating in the tropics and moving south are possible about 12 June to 16 June, 18 June to 22 June, and 22 June to 26 June. Over Western Australia the strongest cold fronts should occur about 8 June to 12 June, 24 June to 28 June, and 28 June to 2 July.
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.