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Predicting the highs and lows

As we know, weather is not an exact science and at times there seems to be more chance of winning first division in lotto than getting the forecast 100% right all of the time!

One element of weather forecasting is predicting the minimum and maximum temperatures. On some occasions, when an anticyclone is overhead and we’re bathed in sunshine, it can be a relatively simple task but take yesterday for example. A humid northerly was blowing over the country and it seemed quite obvious that temperatures would be mild to warm, however more sunshine in certain regions saw the thermometer go considerably higher than predicted.

Auckland looked as if 22 or 23 degrees was going to be on the cards but by the end of the day, 27 degrees had been cracked. Christchurch was looking at about 23 or 24 degrees but the sun prevailed there in the afternoon and a high of 26 was accomplished at the airport with an even warmer 28 in the city.

The Garden City has a reputation of being the hardest city in NZ to predict the daily highs because cool easterlies can give way to warm nor’ westers but the warmer fohn winds don’t always arrive ‘on time’. Sometimes they come too early, other times they are very late and worse, they will sometimes not come at all – perfect ingredients for a forecasters nightmare!  Canterbury forecasters tussle with several options: a) will it reach 32 degrees or b) will the northwesterly not  break through and a high of 20 is likely or c) will the high cloud hover over the city and prevent any warming at all?!

Overnight lows can have their challenging moments too. In Central Otago you can almost guarantee that most winter nights will be near freezing and at the other end of the scale during the summer months, night time temps in the far north are in the mid to high teens.

Of course not everything runs according to plan and I know a few vineyard owners who have been called out in the wee hours of a November morning on the mainland to jump in the helicopter to try and stop frost from forming on the vines – this can happen when suddenly the still night air brings colder temps than predicted and can lead to mass panic amongst horticulturalists!

The predicted highs and lows are often no more than a guideline and while more often than not they’re on the money, there are occasions that nature can play a few tricks and it all becomes a bit of a lottery.

Weather Analyst – Richard Green


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