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Anti-cyclonic gloom affects western coastline

It may have been sunny in many areas on Sunday but not for Aucklanders and others along the west coast.

While highs (or anticyclones) often bring sunny, dry, weather they never guarantee it.  In fact, quite often coastal areas of New Zealand receive at least a day or two of cloudy, or partly cloudy, weather when a large high moves through.

For western areas, such as Auckland, Waikato and Taranaki it’s more common near the centre of the high or to the west of the centre – this is because the eastern side of the high is often accompanied by a gentle southerly flow (due to the anticyclone wind).  Southerlies and south-easterlies often bring sunny weather to the west coast, just as westerlies bring cloud to the west and sun to the east.

The low cloud trapped under these highs is called anti-cyclonic gloom.  It’s low level cloud pushed down and trapped by the high air pressure – and with no winds to blow it away it can often last 24 to 48 hours. 

It usually hangs around the coastline but can’t make it up and over the large hills – so eastern areas on the other side of the ranges normally have stunning blue skies.

It’s especially noticeable when flying – once you takeoff through anticyclonic gloom you climb out of the clouds often in less than half a minute after a take off and into blue, cloud-free skies above.

Sometimes light showers and drizzle can be caught up in them too, usually just around the middle of the low – which we saw north of Auckland on Sunday.

But don’t worry, the gloom shouldn’t last all week with sunnier weather returning throughout Monday and Tuesday to western areas.

On the satellite maps the low level cloud is usually indicated as a very faint grey colour – not as dramatic as big clouds indicated as bright white or orange in most satellite maps.

Image – File, anticyclonic gloom over Auckland in 2010 / Joanne Ottey



Derek on 2/08/2011 2:22am

Hi WW, We have had anti cyclonic gloom over last three days in Whangarei. Get an occasional burst of sun but does not last long..Quite miserable really and temp drop is noticeable.
No rain though so that is a good side.

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