The south of the country was much cooler today and temperatures would be cooler still tomorrow.
"The colder air means that some of these showers are likely to fall as snow over the highest ground of Fiordland, Southland and Otago."
Things were a bit better in the north, with the east of the North Island set for some sunshine later today, he said.
Later in the week, showers were set to become more widespread across the North Island, while an area of high pressure would bring some more settled weather to the South Island from tomorrow.
"After the weekend's windy finish, followed by hefty showers on Monday and Tuesday, we should see finer weather returning to the South Island for the second half of the week.
For the North Island the weather would take a little longer to improve, with better but cooler weather expected to return by the end of the week, Mr Law said.
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Tomorrow's forecast:
Auckland -- Cloudy periods, with a few showers and a southwest breeze. High 17C, low 8C.
Hamilton -- Cloud with the odd shower, then a clear afternoon and then fine. Westerly winds. High 17C, low 4C.
Tauranga -- Mainly fine with a chance of evening showers and light winds. High 18C, low 7C.
Wellington -- Showers develop in the morning with light southerly change. High 14C, low 6C.
Christchurch -- Few showers from afternoon with possible hail and a cold southerly. High 13C, low 3C.
Dunedin -- Few showers from afternoon with possible hail and a cold southerly. High 11C, low 5C.