MetService meteorologist Ngaire Wotherspoon said parts of Southland and Otago woke up to heavy rain that is expected to gradually move northward, with heavy snow forecast for inland areas.
The primary focus is on heavy snowfall predicted around inland Canterbury, south of the Rangitata River and over the Mackenzie Basin, where a warning starts at 5pm and continues into tomorrow morning, with 15 to 20cm of snow expected above 500 meters.
Lower elevations will experience less snow, but with a chance of significant accumulations from about 200m of elevation in inland areas, and 400m closer to the coast.
Additional heavy snow watches are in place for Queenstown Lakes, Central Otago and inland Southland north of Lumsden, along with several road snowfall warnings.
Wotherspoon said the most concerning road warning is for Lindis Pass, where 8-15cm of snow could accumulate around the summit and lesser amounts down to 400m.
“That amount of snow is incredibly disruptive,” she said.
“There’s also a warning for Porters Pass, but we’re not expecting as much snow there.”
As the front moves up the South Island, it is expected to weaken by tomorrow. Rainfall will decrease later in the day on Sunday, and weather warnings are set to expire by 9 am.
“The situation is very different for the North Island,” she said.
Calm weather expected for sold-out Wellington Phoenix game
While the South Island braces for severe weather, Wellington is expected to experience relatively calm conditions tonight.
“We are expecting some showers late at night, but I suspect that will be well after the game itself,” Wotherspoon said.
Although clouds and strong northerly winds are predicted, these should ease off by the afternoon and evening.
A late southerly change might bring showers around midnight, but this will be well after the final whistle.
The A-League Men’s semifinal between Wellington Phoenix and Melbourne Victory kicks off at Sky Stadium at 6.30pm.
Elsewhere in the North Island, the weather is looking favourable.
While there will be some cloud cover in western areas and a few showers near the Bay of Islands later today, these are not expected to be significant, Wotherspoon said.
“Tomorrow, there might be some morning frost in some of those inland areas, we are starting to see some of those cooler temperatures as we head into winter.
“That’ll be the same tomorrow morning for places further south where that front will be clearing ... Invercargill has a forecast low of -3 C tonight, so they’ll be getting a good frost there.”
MetService Road Snowfall Warnings, Issued at 10.23am today:
Porters Pass (SH73) Valid for 8 hours from 9pm Saturday, May 18 to 5am Sunday, May 19. Forecast: 1-2 cm of snow could accumulate near the summit with lesser amounts to 900 meters.
Haast Pass (SH6) Valid for 6 hours from 5pm to 11pm Saturday, May 18. Forecast: 2-4 cm of snow could accumulate on the road south of the summit.
Lindis Pass (SH8) Valid for 14 hours from 2pm Saturday, May 18 to 4am Sunday, May 19. Forecast: 8-15 cm of snow could accumulate near the summit with lesser amounts to 400 metres.
Crown Range Rd Valid for 4 hours from 11am to 3pm Saturday, May 18. Forecast: 3 -5cm of snow could accumulate near the summit with lesser amounts to 400 metres.
Milford Road (SH94) Valid for 3 hours from 11am to 2pm Saturday, May 18. Forecast: 3-5 cm of snow could accumulate above 700 metres, with lesser amounts to 400 metres.
Ben Tomsett is a Multimedia Journalist for the New Zealand Herald, based in Dunedin.