Snow and rain chills Canterbury
MYLES HUME, ABBIE NAPIER AND PAUL GORMAN
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Snow has settled on the Port Hills and inland Canterbury today.
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Snow lies thick on the ground near Methven and has settled along the Summit Rd, on Christchurch's Port Hills.
Earlier fears of flooding for Christchurch have eased.
The MetService has a severe weather watch in place for Mid-South Canterbury and Otago with heavy rain forecast until tomorrow and snow set to fall over inland areas south of Darfield.
"This watch is for possible significant rainfall over lower-lying areas of Canterbury south of Christchurch, and eastern parts of Otago from Dunedin northwards, from later this afternoon through to Saturday night or even early Sunday morning," a spokesman said.
"There is also a possibility of significant snowfalls over higher inland parts of these areas during that time mostly above 500 metres."
Five to 10 centimetres of snow is likely to accumulate above 300m in these areas from this afternoon until tonight, with 10cm to 20cm possible above 500m near the Canterbury foothills.
MetService forecaster Andy Downs said adverse weather may create hazardous driving conditions in some inland areas such as Arthurs Pass, Lewis Pass and Porters Pass. Cold conditions may also cause stress to livestock.
However fears of flooding in vulnerable suburbs of Christchurch have been quashed.
"Significant rainfalls are now looking less likely for Christchurch, however a watch will be maintained for the time being," the MetService spokesman said.
With an expected high of around 5 degrees Celsius today, the MetService is forecasting a miserable weekend for Christchurch which will carry through until Wednesday.
POLAR VORTEX TO PUT END TO MILD WINTER
It was bound to happen - the revenge of the southerly is upon us.
Cold southerlies have been few and far-between to date this winter, while last month was one of the warmest Junes on record.
But that is all set to be swept away over the next week as our icy feed of southerly winds really digs in, bringing spells of rain, hail, sleet and snow.
Computer models even suggest the southerlies could persist until the end of the month, increasing the chances of further snowy periods.
The sudden reversal in meteorological fortunes is due to a change in the strength of the polar vortex - the ring of westerly winds that encircle the Antarctic.
What forecasters call the Southern Annular Mode (Sam), which measures the strength of the vortex, has gone negative.
That means the westerly vortex is weaker than normal, allowing polar air to break out from behind it, close to Antarctica, and head north towards the South Island.
Some models predict the weaker vortex may last into next month.
Victoria University earth sciences Associate Professor James Renwick said high-pressure areas tracked further south when Sam was negative.
''When they move south, that's a recipe for southerlies.
''We're going into the negative phase of Sam. That means less westerlies and a much great chance of more southerlies and cold-air outbreaks.''
Auckland meteorologist Bob McDavitt said the arrival of the southerlies in mid- to late-July - on average the coldest couple of weeks of the winter - could maximise their impact.
''New Zealand is in for a south to southwest flow next week and around the coldest time of the year, so prospects for snow are good.''
Blue Skies weather forecaster Tony Trewinnard said there was ''a risk of snow'' next week.
''But not a likelihood of anything heavy and problematic at this stage.
''[We] need to keep an eye on it, but it's nothing to panic about yet.''
- The Press