Weather: 'Hazardous' wintry temperatures to hit New Zealand this weekend

Even if Cyclone Oma misses us this weekend, there'll be no escape from "hazardous" wintry temperatures.

A colder change is arriving on Friday, bringing with it dramatic temperature drops. Some places are forecast to fall 20degC from recent highs.

"Oma or not, a high impact weather system from the Southern Ocean will likely cause heavy rain, wind, much colder temperatures, and even some snow on Sunday-Monday!" NIWA warns.

"You'll definitely want to stay close for updates on the Sunday-Monday forecast. It could be hazardous. And you might just have to pull out the jumper."

Weather Watch says it's being caused by cold airflow coming up from the Southern Ocean and then being dredged up over New Zealand. This will mean temperatures drop "significantly" this weekend.

"Overnight lows in the upper North Island look set to drop, from the low 20s for a time this week to around 12 and 13degC by next Monday in Auckland," Weather Watch NZ says.

"Sunday and Monday daytime highs around a large portion of Southland, Otago and Canterbury will be just 11 to 14 degrees at the hottest part of the day. In recent weeks these places have highs in the low 30s at times."

But there is good news - for many people this will make sleeping easier.