May 28th: Why its raining, and not raining for others...

There are a few things bringing the current pattern of weather.

Southern Annular Mode - SAM

Have you heard of this seasonal weather driver? This is the one that controls the path of the cold fronts and lows.

A negative SAM (in winter) lets them travel up over Australia, increasing the wet weather.

A positive SAM contracts them, so the fronts only clip the southern coast, and high’s get in the way.

So, if you want rain at this time of year, you like a negative SAM. That’s what we have now.

-> So, tick, the fronts and lows are strong now.

Blocking Highs

The negative SAM is great, but only for one part of Australia. Blocking high’s stop the action for the rest.

This current pattern has a huge block over southwestern Australia (that is where the high is), so there is no wet weather there. Instead, front after front after front is able to cross southeastern Australia.

-> So, tick, nothing blocking the path of low pressure into southeast Australia.

Rain Shadow Ranges - the Great Divide

The terrain of Victoria is very important in which areas get the rain. This is a weather pattern of cold fronts (with no tropical moisture injection ahead of them). So, all the rain comes from the west/southwest.

If there are mountains in between you and the water source (the Southern Ocean), then you are in a rain shadow, and the amount will steadily decrease on the other side.

This pattern ensures that western Melbourne (blocked by the Otways), central and eastern Gippsland (blocked by the Strzelecki ranges and Tasmania), plus all areas north of the Great Divide receive less rain.

Instead, its much bigger falls from southwest VIC, over to western Gippsland, and up into the northeast ranges.

Our terrain:

vic_elevation1.png

The rain still to come over the next week:

ec forecast rain.png

Check the full details for your spot here:

Jane Bunn