June 7th: The pattern changes - what rain to expect in the next week

High pressure has moved to southeast Australia, letting the weather systems peak in the southwest. Then the high controls how those systems move across the country.

A point to note: to make it rain you need moisture and instability to work together. These systems have a feed of tropical moisture - so the moisture part of the equation gets a big tick. The instability part is strong too, but only for those in the right path. You can see that unfold in the shape the rain takes below. It comes down to where the front/low wants to pass through, then the ranges/mountains or distance from the coast play a big part in reducing or building the amount of rain.

The models shown are:

  1. The Euro/EC. Consistently the best, but can over estimate totals in the long term (like they all do).

  2. The new US model (FV3). Better than the original ‘GFS’ by falling into line with the other models much faster, but initial operations show that it is too cold.

  3. The Canadian.

  4. The Australian (ACCESS G). Generally the worst in the long term for now. A new release is coming later this year.

WESTERN AUSTRALIA

Distinct pattern of higher falls near the west and southwest coast, then decreasing as you go inland. Typical strong winter “storm” pattern.

Local falls of 100mm at the coast and generally more than 50mm. At least 15mm in the green areas, at least 30mm in the yellow areas.

Mainly falling on Friday through to Tuesday. Strongest winds are Sunday and Monday.

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SOUTH AUSTRALIA

The pattern shows that the amount of rain this week depends on whether the path of the trough is inland, or closer to the coast.

The highest falls will be 30 to 60 mm, then 10 to 30 mm away from the ‘main zone’.

Keep an eye out for where this one actually moves, to see which areas will see the most.

Falling on Sunday, then most of it Wednesday/Thursday.

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VICTORIA and Southern NEW SOUTH WALES

The ranges will play a big part here, as well as the path of the trough.

The Mallee (and some of southern NSW) will either see hardly anything, or be in line for some of the bigger totals - keep an eye on the path of the Wednesday weather system.

This is not a system for central and east Gippsland. No matter what happens, something that has affected WA will not bring rain to the other side of the Great Dividing Range. Its physically impossible to get over that.

The biggest falls should be on the northern slopes of the Divide, with 20 to 50 mm.

The southwest will do well if the path is a little further south - or its blocked by the ranges like the rest of the south.

Falling on Sunday night/Monday, and again (the bigger one) Wednesday/Thursday.

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TASMANIA

Highly likely that the bigger falls will be in the west and northeast, with more than 30mm, and potentially widespread falls over 50mm. These weather systems are coming down from the northwest, so southeast Tasmania is in the rain shadow.

Mainly falling on Monday and again on Wednesday.

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Jane Bunn