WEATHER

Welcome to our weather page, with information kindly provided by the Bureau of Meteorology.

For up-to-the-minute weather reporting and forecasting, please go to www.bom.gov.au  or download the BOM weather app.

12/09/2019

Don't sweat the small stuff

ENSO this, IOD that, SAM what? Long-range weather forecasting is complicated. Factoring in all of the influences on the months and season ahead can get confusing. But it doesn't have to be with the Bureau of Meteorology's Climate Outlooks.

In the past, the ability to forecast monthly and seasonal weather depended on an understanding of the major influences, or drivers, of our climate. But since 2013 the Bureau has been using a dynamical computer model that accounts for all of the major influences and much, much more—even rare events like the recent Sudden Stratospheric Warming. The state-of-the-art physics- based model uses ocean, atmosphere, ice and land measurements, to simulate future scenarios on the supercomputer.

When the computer forecasts align with conventional wisdom, decision makers can have extra confidence in the outlook. It's one of the reasons why the Bureau provides a commentary on the state of Australia's climate drivers, rather than just churning out raw forecast data.

In Victoria, three of the climate drivers that influence our weather are the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM).

ENSO is a natural cycle in tropical Pacific Ocean sea surface temperatures, wind and cloud. ENSO swings between three phases: El Niño, neutral and La Niña. Typically, an El Niño or La Niña will start in the first half of the year and last until the following autumn. When ENSO is neutral, it has little effect on rainfall and temperature patterns. But during El Niño, Victoria usually has a drier than normal winter–spring, while La Niña usually brings a wetter winter–spring for many areas.

Similar to ENSO in the Pacific Ocean, in the Indian Ocean we have the IOD. Again, the IOD naturally cycles through three phases: positive, neutral and negative. Positive or negative IOD events typically start in autumn and finish in spring. For Victoria, a negative IOD normally means above average rainfall and cooler than average days. In contrast, a positive IOD normally means below average rainfall and warmer than average days.

SAM is the irregular, north-south movement of the strong westerly winds that bring storms and cold fronts to Victoria. And, you guessed it, SAM has three phases: neutral, positive and negative. But SAM's influence changes during the year; a positive SAM in summer usually means above average rainfall in central and eastern Victoria but in winter it's often drier than average in central and western Victoria. Broadly, a negative SAM has the opposite effect.

Victoria's climate drivers interact with one another—they don't work in isolation. So, don't look to just one indicator or driver for guidance on the months and season ahead. Instead, look at the Bureau's Climate Outlooks for the complete picture.

www.bom.gov.au/climate/outlooks

Recent Weather Updates

  • Don't sweat the small stuff | 12/09/2019  

    ENSO this, IOD that, SAM what? Long-range weather forecasting is complicated. Factoring in all of the influences on the months and season ahead can get confusing.
  • Weekly and fortnightly climate outlooks now available | 5/09/2019  

    For the first time, outlooks for the four weeks ahead are now available, closing the information gap between the seven-day weather forecast and the existing monthly to seasonal climate outlooks.