A cold southwesterly airflow / front is set to spread northwards over New Zealand today, starting about the lower South Island this morning then reaching the western North Island overnight.

Northland, Auckland, Waikato & Bay Of Plenty
Conditions may be dry first thing then showers spread into most areas during the morning from the west, expect sunny spells at times. Showers ease in the evening with long dry spells developing then overnight heavy showers move into western regions. Westerly winds.
Highs: 15-17

Western North Island (including Central North Island)
Rain about Taranaki spreads elsewhere during the morning, easing in the afternoon as northerlies tend northwest then clearing by evening. Overnight heavy showers move in with a chance of thunderstorms.
Highs: 12-15

Eastern North Island
High cloud, a few spots of rain possible during the afternoon / evening. Light northwesterly winds.
Highs: 15-17

Wellington
Mostly cloudy, spots of rain mainly from afternoon then clearing in the evening. Northerlies tend northwest late afternoon.
High: 13

Marlborough & Nelson
Morning high cloud with a few spots of rain then becoming mostly sunny in the afternoon, cloud thickens up again overnight with further spots of rain. Northwesterly winds.
Highs: 14-16

Canterbury
High cloud with light winds, late afternoon or evening southwesterlies freshen about South Canterbury bringing showers then rain later. Rain may become heavy then overnight this rain moves into North Canterbury. Snow lowers overnight to 400 or possibly even 300m south of Banks Peninsula, 500m further north.
Highs: 12-14

West Coast
Early heavy rain then easing to mostly cloudy skies and the odd shower, rain picks up again from afternoon about South Westland then moving into North Westland in the evening. Northwesterlies change southwest overnight.
Highs: 10-12

Southland & Otago
A mainly dry morning with high cloud, there may be a spot of rain. Showers develop about Southland towards midday as cold southwesterlies freshen, these showers move into Otago late afternoon becoming heavy. There may be some hail at times with showers and snow flurries lower to 400 or perhaps 300m in the afternoon about Southland then overnight for Otago.
Highs: 8-12

By Weather Analyst Aaron Wilkinson – WeatherWatch.co.nz