Storm cuts road

DAVID HALLETT/The Press

UNSEASONAL DUMP: hail coats a hillside near Porters Pass after yesterday's storm.

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Thunderstorms dumped torrential rain on the Canterbury foothills last night, blocking the main highway to the West Coast at Castle Hill and causing surface flooding in the Weka Pass.

Debris from the downpour blocked the State Highway 73 bridge over the Thomas River, near Castle Hill, making the road impassable from about 6pm.

As the storm eased traffic began using the bridge again about an hour later, police said.

Surface flooding and small slips were also reported in the Weka Pass, on State Highway 7.

Castle Hill village resident and guest-house owner Phil Stephenson said the downpour was "the heaviest rain burst in 10 years".

"It lasted a good couple of hours. There was hail and a river through the streets."

Stephenson ventured out onto the street and reported stormwater drains had broken and the road was missing seal in places.

Auckland tourist Doug Anderson, who was renting a bach in the village after his wife had run the Coast to Coast, said the teeming rain had flooded his garage with up to 7cm of water.

After the deluge the streets were carpeted with hail, he said.

The MetService said the thunderstorms were caused by a layer of warm, moist air under a cooler upper layer, with the foothills acting as a trigger.

The thunderstorms also brought large hailstones and more than 3600 lightning strikes were recorded in Canterbury, North Otago and the Nelson Lakes in six hours from yesterday afternoon.

Severe weather forecaster Andy Downs said gauges in the central Canterbury foothills recorded between 30mm and 55mm of rain in an hour late yesterday afternoon, enough to cause flash flooding.

He said the thunderstorms weakened as they moved east, skirting to the north of Christchurch last night.

Downs said rain and showers were expected overnight and today. Unlike the heavy downpours which tended to run-off the dry ground, the rain that followed would be more useful for parched areas of North Canterbury. Earlier yesterday temperatures peaked in the high 20s around the region.

Cool, showery weather was expected to slowly clear today.

- © Fairfax NZ News