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What Antarctic storm? It’s 20 degrees right now!

Forget the winter blast last week – as predicted by last Wednesday the spring warmth has raced back into a number of regions today.  In Christchurch the mercury has risen to 20 degrees with a westerly breeze, with other parts of Canterbury hovering around the 20 degree mark.

But unlike last week the air today isn’t coming from the Southern Ocean – it’s instead coming from South Australia and up over the Southern Alps.

Weather Video: Watch Philip Duncan talk about the weather this week and weekend across NZ, plus the latest on Hurricane Irene

As the air moves over the ranges it deposits most of the moisture on the West Coast and the drier, warmer, air moves over the east coast.  “The dry air moves quickly down the eastern side of the Southern Alps and that friction heats it up even more” says head weather analyst Philip Duncan.  “As we head into spring we’ll see more and more of these 20 degree days with highs in the mid 20s possible coming as early as September”.

But Mr Duncan says farmers shouldn’t become complacent with both and NIWA warning of the possibility of more snow storms.  “We don’t see anything in the next week or two but that risk remains with us up until the end of October, we have that type of weather pattern this year”.

Despite the cold blast last week winter has, overall, been mild for most places.  Even last weeks cold blast was short lived, hanging on for less than 7 days before the warmer weather returned.

What are weather conditions like where you are today?  Post a comment below!


Guest on 24/08/2011 2:29am

Is there any particular influence that will cause days as high as the mid twenties in september (possibly), or is this just normal….. what about Chch, we’ve had days up to 28 in September before, could we get some high temps this spring? Whats the overall outlook? (Sorry about the lengthiness)!

WW Forecast Team on 24/08/2011 2:37am

Usually the air comes from Australia when we see the South Island hit high temperatures.  For example earlier this year when Timaru had the heatwave and hit 42 – the air was coming off Australia where they had also had a heatwave.  So the air is warm and fairly dry already.  Usually that’s our best bet for temps 25+.  So track the isobars and see where they come from – if they stretch into the tropics or out over Australia you know that we’re in for some heat.  Cold nor’westers happen too – this is when the air is coming from the Southern Ocean and the warming affect over the Southern Alps isn’t so noticeable (ie, 14 degrees in Greymouth, 16 degrees in Christchurch).

The angle of the wind, the source of the air and the time of year all contribute to the big and not so big highs with a nor’wester.  Can be very tricky to forecast too.

– WW

Guest on 24/08/2011 1:54am

I’m not sure if “friction” is what causes the warmer weather on the other side of the moutnains. I think it has more to do with the the pressure / compression acting on the air?

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