Looking back to a Spring storm and ahead to settled weather

With a slow moving ridge over New Zealand bringing few weather worries for the start of the week ahead, we have a chance to review how extreme our weather can be. During the latter half of last week, a warm, northwest flow picked up a huge amount of moisture as it crossed the Tasman Sea, and dumped it on the West Coast and Southern Alps. Then, on Friday, a cold front from the southwest moved over Canterbury and Otago, undercutting the moisture-laden flow aloft and resulting in significant snowfall there.

In terms of rain amounts, Westland Council’s Cropp River Waterfall rain gauge recorded 793mm from Wednesday 7th to Friday 9th November , 631mm of which fell on Thursday 8th. To put that into context, rainfall totals for 2018 up to the end of October in Auckland, Wellington and Christchurch are 1083mm, 1027mm and 694mm respectively. Rivers on both sides of the Alps rose rapidly, which resulted in flooding, slips and bridges on the West Coast being washed out, as well as the tragic death of a person when a river bank collapsed on Thursday.

“One the hardest aspect of that event to forecast was the distribution and amount of snow expected,” said Meteorologist Rob Kerr, “with the significant Canterbury and Otago snowfall resulting from the precise alignment of the surface cold front from the southwest, and the moist conveyor belt aloft during Friday morning,” he added.

“The start of the week ahead is much more like summer than the weather conditions many saw last week, with a broad ridge of high pressure dominating proceedings. Fine weather and light winds will be the story for most, so make sure the sunscreen is handy, but keep a look out for afternoon or evening showers bubbling up over inland parts of New Zealand,” he concluded.

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