Weather: Southerly blast howling up North Island

The North Island is next in the firing line as a cold southerly blast works its way up the country.

Fresh from dumping snow on the South Island on Tuesday night, it now prepares to blanket the central North Island on Wednesday.

"A southerly blast, the second one in a week, is today pushing into the North Island after last night bringing snow to Southland, Otago and Canterbury for a time," Weather Watch warns.

Snow is expected to hit the North Island down to as low as 400m-500m, with road snow warnings out for Desert Road, Remutaka Hill Road, and the Napier to Taupo road.

"Snow may now affect North Island highways later today and into Thursday morning, especially SH1, the Desert Road, and SH5 - the Napier to Taupo highway" says Weather Watch head forecaster Philip Duncan.

"Hail showers to sea level are possible in both islands as the cold change sweeps through".

Localised heavy rain and isolated thunderstorms will be possible and winds may be strong in exposed coastal areas.

Minimum temperatures will be 4degC to 8degC in most areas tonight but might not drop into freezing levels lower down due to winds or cloud cover. However frosts are most likely well inland.

"By Thursday frosts return to the South Island interior but the daytime highs do start to lift - while Thursday looks to be the North Island's coldest day this week," Weather Watch says.

"By Friday most places are back to 'normal' under a big high. That high looks to dominate the North Island this weekend and will encourage westerlies over the South Island."