MetService’s road snow warnings for the district’s alpine passes have helped keep locals safe on the road for many years, but this year the national weather authority’s warnings have been a little less reliable than usual.

MetService has issued around 12 snowfall warnings so far this month, and so far only a handful have predicted snow accurately.

Wānaka App co-owner Tony O’Regan has been updating road conditions daily for eight years, including snowfall forecasts that impact alpine passes.

He said the forecasts had been less accurate this winter than in previous years.

The Wānaka App went to MetService with a few questions about the accuracy of its forecasts, and its record keeping.

Communications meteorologist Andrew James said it was “challenging” in the first half of this winter to get “the exact combination of ingredients right in the marginal cases”.

“There are many variables that affect snowfall – temperature through the atmosphere, wind speed, temperature of the road, freezing level, precipitation, time of day and others too.”

Most of the MetService’s road snow warnings are not routinely verified, and Andrew said the authority is “currently exploring options for verifying our road snowfall forecasts”.

“Observing snowfall amounts is problematic,” he said. 

“For most roads, we estimate snow depth from webcam images, infer snowfall from temperature and precipitation at nearby weather stations, or get ad hoc reports from people on the ground.”

Road snow forecasts are issued as part of MetService’s contracts with the Ministry of Transport and NZTA Waka Kotahi to keep New Zealanders safe and informed, he said

“Whenever there is a risk of any snow affecting even the summit of a road our team will issue a road snowfall warning.”

Andrew added that the paucity of snowfall this year is “partly down to the warm northwesterlies that dominated the weather across New Zealand for the start of winter”.

“However, over August we have seen the winds turn more southwesterly and this has brought with it the return to colder weather and the risk of snowfall.”

PHOTO: Wānaka App