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The Big Picture: Warm air out, Cool air in

Is it a cool change, a cold change or a normal change?  Temperatures over the next 12 to 24 hours will drop nationwide as the large low that has caused so many problems around the country crosses northern New Zealand, moves out to sea, and drags in a “cooler” south to south west wind change.

Yes, it will feel ‘cold’ compared to how mild it has been lately – but much of the air moving in this weekend will bring temperatures back to more normal levels.  Therefore – it might feel cold in comparison…especially in the wind. 

However the temperatures aren’t really what we, as forecasters, might class as “cold” as we don’t see major wintry conditions moving in.

Why the big temperature change?

With low pressure systems in the Southern Hemisphere winds spin around them clockwise – and highs spin anticlockwise.  This means the low (when it was south west of NZ) was pulling down warm northerly quarter winds for many regions of NZ.  With the low soon to be north east of NZ we get the tail end southerlies spreading up over us.  

Add on top of that a powerful high around Aussie’s east coast and that helps fuel the south to south east wind flow around New Zealand too…the high and low work in tandem to dredge up cooler air from the Southern Ocean.

So, in a nutshell – the air over New Zealand won’t be spreading down from the sub-tropics for the next several days – instead it will be spreading up from the Southern Ocean area.

The cooler air will certainly be noticeable  – and we won’t argue with anyone who thinks it’s ‘cold’ (and no comment on if we had our heat switched on as we were putting this graphic and story together!).

Have a good weekend!

(C) –


Serenity on 15/05/2015 7:10am

These big picture summaries are great 🙂

WW Forecast Team on 15/05/2015 9:49pm

Many thanks! We’re working to improve them further and have more of them – early days at the moment 🙂
Thank you for the feedback
– WW Weekends

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