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A tale of two lows

A real battle will be taking place over the skies of New Zealand this weekend.

First, a little background.

High pressure means sinking air.  The big “H” that you see on a daily weather map means that the air under the influence of that “H” will be sinking.  This is also known as a “stable” atmosphere.

Showers and thunderstorms don’t like a stable atmosphere.  They want drama.  They thrive on instability.

This is why high pressure usually means settled weather.  It’s also why lows often bring us unsettled weather.  They contain unstable air.

Fast forward to Saturday.

It looks like we are going to have a ridge of high pressure draped across the islands.  Like taking a piece of chewing gum and stretching it out from the Tasman Sea to the southern Pacific.  It is going to do it’s best to keep most of the country dry this weekend.

Working against that high will be two lows.  One to our north and one to our south.

The one to our south looks like it will stay well south of the country.  It may try to throw some rain northward into the south Island, that ridge of high pressure is going to try to keep it away.

On the other end of the country is a low coming out of the tropics.  This too will try to spread rain into New Zealand.  This too will have to fight the ridge of high pressure in order to do that.

So who is going to win?

At this point, it looks like the two lows will be able to spread enough moisture and energy across the islands to make for a somewhat unsettled weekend.

Saturday looks to be a bit rainy over most of the South Island.  A few showers here and there with some dry breaks.  Sunday is looking a bit more settled.

For the North Island, Saturday looks to be the better day.  Sunday rain may spread across the Island.  But right now it looks to be a mainly late afternoon event for all but the Bay of Plenty.

From WeatherWatch Analyst Howard Joseph

Photo by Tony Kissel


Guest on 4/01/2012 1:38am

…yet more rain!!!! Usually get a bit of a tan in summer…this year it’s rust!!!!

Guest: "Wally B"(Kawau Is) on 4/01/2012 12:07am

Who says the weather is boring – this report reads like a novel..look forward to the next chapter!! Welcome to NZ Howard.! A Happy New Year to all at WW

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