South Islanders are starting to feel the effects of the a cold snap forecast to bring snow to some alpine areas today, while in the north rain is causing trouble for some.

State Highway 1 was closed between Otaki and Levin due to surface flooding just before 5.30pm, but reopened an hour later. Motorists were also warned to expect delays on SH2 as some sections of the Rimutaka Hill road were down to one lane because of slips.

However, all alpine passes remained open as of 6pm, after the Metservice earlier today warned motorists in the South Island and the North Island's Desert Rd to take care as the southerly change brings snow down to 500 metres above sea level in some places.

While the dusting won't arrive in the North Island until the early hours of tomorrow, the southerly was making its way up the South Island this afternoon.


Arthur's Pass Alpine Motel owner Fiona Neale said snow began falling close to the alpine settlement between Christchurch and Greymouth mid-afternoon.

"We had about half an hour of snow down to about 850m, so it's in the treetops."

There were also snow showers at nearby Porters Pass today, and, in the North Island, falls of between 2-4cm were expected to accumulate near the summit of the Desert Rd overnight. Dustings are also expected on Milford Rd, north of Te Anau.

However, up to 5cm was expected on the Lewis Pass, SH7, this afternoon, with lesser amounts down to about 500m.

Maruia Springs Thermal Resort managing director James White said about 5.30pm it had just begun to snow about 150m above the resort, which is 600m above sea level.

"It's looking like a winter wonderland at the moment. The temperature has dropped in the last couple of hours, it's definitely winter."

The unusually warm June temperatures - where Auckland's 19.9C was one of its highest June temperatures recorded - are now coming to an abrupt halt.

In Christchurch the high reached 13C today, but had plummeted to 5C by nightfall.

Dunedin was marginally warmer, at 6.6C just before 6pm, while the capital was 7.8C but "felt like" a bone-chilling 3C according to the weather service's website.

Duty meteorologist Peter Little said the cold front would be followed by cooler southerlies that would see temperatures plummet to more usual winter levels.

"Over the lower South Island will be single digit maximums and those temperatures over the North Island which we have seen in the high teens or early 20s as the southerly blows through tomorrow they will be more early to mid teens."

The fronts were also forecast to bring heavy rain to the upper South Island and Tararua Range, with a low risk of thunderstorms over northern Marlborough and the west of the North Island up to Auckland this evening.

However, there was some good news on the horizon as a ridge of high pressure makes its way towards the country. For the South Island that would mean clear skies, little wind and, inland, severe frosts.

WeatherWatch analyst Philip Duncan said tomorrow morning would be a bit cooler for many, but the week will generally be dominated by westerlies in the lower two-thirds of the country and more high pressure and lighter winds in the north.

Most showers this week will be confined to the West Coast. Temperatures should be around average to slightly above average overall in most places.

• Mon 16C, sunny
• Tues 18C sunny

Mon 15C, sunny, chance early shower
Tues 17C sunny

Mon 13C, sunny
Tues 16C, sunny

Mon 15C, sunny
Tues 17C, sunny

Mon 13C, mostly sunny
Tues 15C, sunny

Mon and Tues 14C, fine and frosty

Mon and Tues 15C, fine and frosty

Mon 12C, fine and frosty
Tues 13C, fine and frosty