Weekly Update: 21st March 2025

Big rainfalls moved through parts of southeastern Australia and this week we focus on why some parts received huge rain and others hardly anything.

In order to make it rain you need two things to work together: moisture and instability.

The moisture side of the equation has a huge tick mark, the instability is the variable part.

As long as high pressure is 'in the way' then low pressure can't move into the spots that most need the rain - especially these areas in significant drought in the south:

The latest rain system delivered big falls further east of these drought zones, but once again missed these key drought-affected areas:

What will the next few months look like?

Moisture

Australia is surrounded by warmer than average water, so there is more moisture available to us than 'normal'. This has been the case for the past five years, either in La Nina, or El Nino (as the drying trend was offset by this alternative source of moisture), and in a negative or positive IOD (again as the drying trend was offset by this alternative source of moisture).

- 2025 is showing weak signs of heading into El Nino (or close to) later in the year (later Spring/Summer), with neutral conditions before that.

- 2025 is showing stronger signs of heading into a negative IOD in Winter, with neutral conditions before that.

So that's the Indian Ocean sending moisture our way, and the Pacific suppressing it - but the waters around Australia offset that suppression.

Moisture gets a big tick.

Instability

This is the hardest thing to forecast.

We don't have confidence in where a weather system will move a week out, let alone the next few months or year.

One climate driver to look at is the Southern Annular Mode (see daily updates here - scroll to the SAM map).

If that is positive (as it was for much of the past year) then it encourages high pressure to sit across southern Australia. It doesn't tell us where it will sit, but it is one factor in stopping big rainfalls from reaching those drought affected areas - just like we saw with the most recent weather system.

For my full analysis settle in for my weekly update video:

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In this series I'll take you through the drivers of our weather, highlighting any changes over time and things to watch out for (generally every Friday). It covers weather elements like temperature and rainfall, and how they are driven by moisture from the Pacific and Indian Oceans, as well as bursts of energy from low pressure (SAM and MJO).

See and hear my commentary as I take you through the weather pattern's effects on our rain and temperatures in detail over the next week, with a brief look at week 2 and beyond as well.

Plus what is driving our weather in the weeks and months ahead, with the latest on El Nino/La Nina, the Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM controls our weather systems), and the Madden Julian Oscillation (MJO connects tropical moisture to our weather systems).

I update this commentary each week, generally on Friday's. Make sure you are signed up (free or a subscription) so you don't miss an update.

Stay up to date with the forecast specifically for your area in our hour by hour outlook for the next 10 days. Download our app for iPhone and Android.

As always, you can see each of these graphics as soon as they update, as well as more information about them under our Rain Outlook and Seasonal Outlook pages within Jane's Update, along with our Snow Forecast in the snow season.