Perth 28-day rainfall forecast
Chance of rainfall somewhere within district
Issued 14 Nov 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 southwest Indian Ocean, the Indian Ocean, New Zealand, and South America. Summary: Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 20 November to 24 November, 3 December to 7 December, and 17 December to 21 December. Rain events originating in the tropics and moving south are possible about 20 November to 24 November, 29 November to 3 December, and 7 December to 11 December. Over Western Australia the strongest cold fronts should occur about 20 November to 24 November, 3 December to 7 December, and 17 December to 21 December.
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.