Summary
Below median rainfall for autumn (March to May 2024) in the South West Land Division is indicated by half of the national and international models.
Further ahead, the majority of models are indicating neutral chances (neither below or above median rainfall) for winter (June to August 2024).
Warmer temperatures than normal are expected to continue.
Things to consider:
- Year to date rainfall was above average for some parts of the South West Land Division (SWLD), from ex-tropical cyclone Lincoln, on 24-25 February and a series of thunderstorms in January. Plant available soil water is variable.
- Bureau of Meteorology temperature outlook for autumn (March to May 2024) is for above average maximum and minimum temperatures. There is an 80% chance of exceeding median temperature.
- El Niño is continuing in the tropical Pacific Ocean but is expected to decay by May.
- From the models surveyed by the Bureau of Meteorology, 2 out of 7 are indicating a La Niña to develop in the Pacific Ocean by July. Remember skill is poor at this time of the year.
- The Indian Ocean dipole is now decayed. One out of 5 models is indicating a positive Indian Ocean Dipole in July.
- Rainfall is forecast for 3-7 March, with up to 15-25 mm for the central Wheatbelt and Great Southern forecast districts, from a period of tropical activity north of Australia, driven by intra-seasonal variations.
Rainfall outlook for the South West Land Division
A summary of 20 national and international models show that 10 models indicate below median rainfall for the SWLD for autumn (March to May 2024).
Further ahead, the majority of models is indicating a neutral chance of exceeding median rainfall (neither above or below median rainfall expected) for winter (June to August).
A neutral outlook doesn’t mean average rainfall, but normal climatology (anything is possible).
Remember, however, the further out the model forecasts, the least skill it has. Also, because of the ‘autumn predictability barrier’ climate models forecasting past autumn (March to May), have the lowest skill and should be viewed with caution.
The Bureau of Meteorology in their climate outlook webpage, gives the rainfall outlook for individual locations 5 months ahead. Example below is for Coorow, with average rainfall expected in June.
The bar graphs show the variability in the ensemble run of the Bureau’s ACCESS model, and the stars indicate the skill of the model. There is lower skill the further out the outlook is.
Climate driver outlook
The Bureau of Meteorology’s survey of international models suggests ENSO to be at neutral state in July. Although, 2 out of 7 models is indicating a La Niña to develop.
La Niña has variable influence on the SWLD climate. The last La Niña was in 2020, a decile 2-3 growing season rainfall year.
The Bureau of Meteorology survey for the Indian Ocean Dipole, shows one model indicating a positive Indian Ocean Dipole.
A positive IOD generally means drier winter-spring rainfall and warmer temperatures for the SWLD. The last positive IOD was in 2019, a decile 2-3 growing season rainfall year.
Remember, that we are currently in the ‘autumn predictability barrier’ for forecasts, which means models predicting past autumn must be viewed with caution as they have the lowest skill at this time of the year.
For information on climate drivers refer to the Bureau of Meteorology’s Climate Driver Update.
Recent Climate
1 January to 28 February rainfall was above average for the majority of the South West Land Division. Highest amount was in Esperance with 102 mm.
Bureau of Meteorology’s Water and the Land, which is a consensus of 6 national and international models, is expecting between 5-25 mm of rain for 29 February to 7 March from a period of tropical activity north of Australia, driven by intra-seasonal variations.
