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Weekly Update: 4th April 2025

Jane Bunn

Rain is contracting northeastwards through Queensland with a quiet period ahead for much of the state. A low delivers 25 to 50 mm of rain for a large part of the southwest over the next few days. Cold fronts slide across the southeast bringing bursts of cold air, but little if any rain for those inland as there is no connection to tropical moisture.

Potential rain over the next week
Potential rain over the next week

The Pacific Ocean is currently neutral and is likely to head towards El Nino later this year.

This stops tropical moisture from being pushed towards Australia - however, we have our own source (all the warm waters off the east coast) to offset this drying trend.

The Pacific Ocean is neutral, and may go near El Nino later in the year
The Pacific Ocean is neutral, and may go near El Nino later in the year

The Indian Ocean is currently Positive and remains near there for the next few month - also working to stop tropical moisture from being pushed towards Australia - however we also have incredibly warm waters off the west coast, so we also have our own source of moisture to offset this drying trend.

Later in the year the modelling has it nearing or potentially crossing into Negative. This works to push tropical moisture towards Australia - so that's a double dose from the west.

The Indian Ocean is Positive and remains near that for the next few months, before tending Negative later in the year
The Indian Ocean is Positive and remains near that for the next few months, before tending Negative later in the year

So, despite a potential El Nino, and the current Positive IOD, we have our own sources of moisture.

That's just one part of the rain equation - you also need the moisture to run into low pressure to turn it into rain.

That's determined by the weather pattern.

When a climate driver known as SAM is Positive, the pattern is dominated by troughs and lows. These are very polarising, bringing rain to one side, but leaving it dry on the other. Those to the north and east pick up the rain... those the south and west do not.

A Positive SAM also limits the strong cold fronts, instead giving us sliding fronts like we're seeing this weekend in the southeast. It encourages high pressure to become stubborn and block the connection between tropical moisture and the weather systems in the south.

All of this leads to a lack of rain, no matter how much moisture we have to play with.

We don't know what SAM will do this year, but so far it has been fairly Positive... and it was Positive for the majority of last year which led to significant drought for those southwest of the low pressure that didn't see the regular cold fronts they are used to.

The Southern Annular Mode (SAM) shows lots of positive or near positive, indicating troughs and lows are more likely to feature on the weather map
The Southern Annular Mode (SAM) shows lots of positive or near positive, indicating troughs and lows are more likely to feature on the weather map

The Bureau's latest outlook reflects this picture... better odds for rain to the northeast, and lower odds to the southwest.

The Seasonal Outlook from BoM reflects that tendency for troughs and lows rather than strong cold fronts
The Seasonal Outlook from BoM reflects that tendency for troughs and lows rather than strong cold fronts

For a full update, don't miss my video, walking you through all of this in detail:

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