Wednesday sees the start of a cold outbreak which will progress during the day over the South Island. In the north, however, while becoming wet in the west, it will still be reasonably warm, especially on the east coast where temperatures in the high teens are possible.
Increasing northwesterly winds affect much of the North Island in the west with increasing cloud, while rain moves onto the southwestern corner of the North Island in the afternoon, then reaches the likes of Auckland later in the evening. Heavy falls are possible as this front moves through. The East Coast is mainly dry although spots of rain do spread into the Wairarapa at times. Hawkes Bay and Gisborne may not see any spots of rain till evening.
For the South Island, we see rain for the West Coast from morning, possibly heavy, then easing during the afternoon. From afternoon, rain becomes fairly persistent about Southland, Otago and perhaps parts of South Canterbury. Overnight rain pushes into the remainder of the east of the South Island with a chance of a few heavy falls, more so inland.
Snow will move into different parts of the South Island at different times during the day due to the complex nature of a pair of low pressure systems moving over the South Island. It must be said that the current forecast could change a little, as a subtle move in a front could result in a fairly large difference come Wednesday, for a few areas. At this stage, snow is looking to fall to around 600m about Southland, Otago and parts of South / Mid Canterbury, then push northwards overnight. Snow lowers overnight to 400 or perhaps even 300m from Mid Canterbury southwards. Snow is looking to be heavy in the high country for most, although not becoming heavy for North Canterbury till overnight.
– Aaron Wilkinson, WeatherWatch.co.nz