All the weather action is in the southeast

Our weather pattern has the combination of large areas of high pressure and a lack of moisture feeding in from the tropics.

High pressure is the antidote to wet weather, as it’s the exact opposite to instability, one of the key ingredients for rain.

A lack of tropical moisture (the other key ingredient for rain) is thanks to a climate driver known as the Madden Julian Oscillation (MJO). The MJO is a pulse of energy that travels around the globe in the tropics, and wherever it is visiting gets an increase in wet weather. It’s currently over the western Pacific - just out of reach of Australia, but will help deliver huge rainfalls over the next week to our Pacific neighbours. 

It’s not all dry though. The southeast has a very active weather pattern.

High pressure can’t cover everything, and the southeast is missing the guard at the door. There’s no bouncer at the nightclub and any bit of low pressure can walk through. 

Tasmania is copping the full brunt of this open door system with cold front after cold front sailing through. They come in from the west, so the western ranges are seeing 100 to 200 mm of rain over the course of a week. The terrain in Tasmania means that the east is on the dry side of the ranges and receives a lot less. 

High pressure is just far enough north that southern Victoria catches these fronts from time to time. Not a direct hit like in Tasmania, but more like a brushing of the edge of them, producing an increase in showers as a front passes. This adds up to 25mm at best over the course of a week for exposed parts, while most see less than 5mm - and if you are inland it’s a bit of cloud and not much else.

The series of fronts could have a shake up early to mid next week. A ‘cut-off’ low pressure system could come to the party. 

Cut-off is the important part here, as it’s separated from the fast moving westerlies to our south, that would usually whisk these systems through at a great pace.

When the low detaches from this conveyor belt it is at leisure to wander through at a slower pace - and slow moving low pressure means an increase in rain for those in its path. 

A slow moving low is a great producer of rain, but it is only half of the rainfall equation. You also need moisture. We like that feed to be tropical as it holds a huge amount of moisture. But even a feed of moisture from the Southern Ocean can make for a decent rain system.