Temperatures plummet as high pressure spreads

Could we see temperatures dropping to - 10 this weekend? Temperatures look set to plummet as a ridge of high pressure spreads over the South Island and southern and western North Island later this weekend bringing little wind and clear skies to inland regions.

In the past few days we've seen temperatures drop to - 5 in the eastern Waikato and Taupo, - 6 in Tokoroa and - 7 on the Desert Road. We saw - 8 on some of the ranges of Southland and that was during cloudy, windy, conditions. So under clear skies and little wind is it possible that we'll see the mercury fall to - 10 in some centres? Well there are some things working against this. Firstly, it's been a number of days since that polar air was delivered to us... it's certainly had a chance to warm up a little under the sunny skies Secondly, winds may turn a little more westerly for a time...which may flush the coldest air out of Central Otago (an area well known for 'holding in' the coldest air). Thirdly, the top right hand side of the high will be over the north eastern part of the North Island meaning south easterlies may blow over the next few days, limiting frosty conditions in places that often get the coldest North Island weather such as Taupo, Tokoroa, Rotorua and Waikato.

The ideal weather conditions to get to - 10 and colder is to have a high move in within 24 hours of a cold snap. The cold arrives, settles in the valleys, then instantly the high comes in to 'lock it in'. But even if we don't make it to - 10 it's still going to be very cold this weekend at night in southern and western areas. Sunday night and Monday night may see the most widespread frosts of the week.

Southerly winds have been affecting Auckland and other regions for a number of days now and they aren't going anywhere else soon. In fact, winds from the southerly quarter will affect the northern and eastern North Island until mid next week. It's helped keep temperatures well down but due to sunny conditions it's been relatively pleasant.

I had to get a couple of small things fixed on my car yesterday and the mechanic mentioned I must know it's about to get warm because I was wearing a t-shirt. Thing is, I don't really feel the cold so much. I love sleeping with a window open or even a fan going. I just don't like the air being 'locked up'. Besides it wasn't cold in Auckland yesterday...well, it was if you were in the shade, but in the sun it was lovely. In New Zealand you're pretty safe with a sunny, wind-free, day. Chances are even in the middle of winter, no matter where you are in New Zealand...if there's no wind and clear skies the temperature will most likely be around the 9 to 13 degree mark. So I wear a t-shirt. It's something we as New Zealanders may take for granted...our warm winter days. I remember being in Canada in spring - that's right, not winter, but spring...we had clear skies and only a very light breeze. It looked warm. So I went out in a t-shirt and jeans....it was - 25 in that "light breeze". I think I lasted 3 footsteps before the pain hit me. Even the lightest of breezes felt like a million needles stabbing my face and making my lungs shrink (and that wasn't all that shrunk). I don't know how Canadians live in conditions that cold. Not to mention being trapped in doors all day because it's too cold to go out. It's unthinkable to go to sleep in winter with your window open a crack too (which I did...good ol' Kiwi-boy).

So enjoy the sunny, cold but pleasant, weekend - and make the most of getting outside in the dry weather. If July is anything like last year we may be rained out.

Philip Duncan

Pictured above: Frost on a staple on farmland east of Waikanae on the Kapiti Coast. Photo / Mark Mitchell