A mild end to July but will winter return in August?

Wednesday, 24 July 2019

MetService meteorologist Georgina Griffiths talking about 'SAM' - the Southern Annular Mode or polar vortex, which plays an increasingly important role in determining our weather.

It's been another soft winter, with little sign of any major wintry outbreaks on the way as August looms.

For most Kiwis, this winter, so far, peaked in the first week of June.

Southerly gales blasted parts of central and southern New Zealand on the first two days of June, with heavy rain close to the coast and alpine passes blocked by snow.

A cold July morning with shallow fog patches in Hagley Park, Christchurch.

A few days later it was much of the North Island's turn, when another deep depression crossed the country.

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This winter's only significant snow on Porters Pass, which came on the first day of June and the first day of winter.

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Snow at Lake Lyndon about 10 days after the big snowfall that closed nearby Porters Pass on June 1.

Since then, winter has largely been free of significant rain and wind storms, with the kind of weather that comes as a result – some frosty mornings, and plenty of fog and drizzle lingering long into the day and out staying its welcome.

Forecasters can't see any huge change in the next week, although some computer models have been showing there could be the first cold southerly in a while around the first few days of August.

There have been many foggy days this winter, due to mild, damp air masses. Cars emerge from the fog on Stuart St in Dunedin.

It has been another winter with a lack of bitterly cold polar southerlies. In Christchurch it is now more than seven years since snow last settled in the central city and lasted longer than a few minutes. That was on June 6, 2012.

Blue Skies Weather forecaster Tony Trewinnard told Stuff the weather pattern for the next six weeks looked 'relatively settled'.

'We are stuck in this slack pressure zone this week, and next week will be more of a southwesterly week. There might be one or two rain events next week.

'It looks as though August will be mostly westerly or southwesterly airflows, so fairly settled and fine, dry.

'There are a couple of unsettled periods possible around the middle of the month and at the end of August, but it doesn't really look at this stage ike it will build up to anything major.'

Looking further ahead, spring might be 'reasonable active' with westerlies and there was a chance of a summer La Niña, Trewinnard said.

'That would potentially mean fewer west or northwesterlies and more east to northeasterly days. That would also increase the risk of tropical cyclones coming down this way later in the season. But it could be dry on the West Coast and in the south [of the South Island].'

La Niña – the opposite of El Niño – often brings mild, wetter weather to the east and north of the North Island. The South Island's east coast can also be cloudier than usual with more frequent rain than in most summers.

MetService meteorologist Georgina Griffiths said there would be 'a mixed bag of weather patterns for the rest of the month', which was fairly typical for late July.

WeatherWatch head forecaster Philip Duncan said New Zealand was now entering what was traditionally the coldest four weeks of the year.

'Westerlies return next week but look weak over most regions. There is a lack of frosts for this time of the year and no severe frosts in the forecast, and a lack of lower level snowfall for the ski fields and almost no snow for the tops.

'It will be drier than average almost everywhere in New Zealand this week, except coastal eastern areas between Gisborne and Masterton.'