The small slip blocked part of the left southbound lane making for a long trip into the city for commuters.
There are also heavy rain watches in Taranaki, Taumarunui and Taihape.
Further north, a strong wind warning is in place for the Hauraki Gulf and the area from Bream Head to Cape Colville.
MetService has lifted a heavy rain warning for Buller and Westland.
No further widespread heavy falls are expected although heavy showers are possible and thunderstorms are likely until late afternoon.
A heavy rain warning has also been lifted for the headwaters of Canterbury lakes and rivers.
But motorists are being urged to take care with snow expected on some roads including Porters Pass, Lindis Pass and the Crown Range Road.
Between 1cm and 4cm of snow could settle.
"It won't be a very big dump but it could be significant for motorists," Haddon said.
Strong wind watches are also in force around Wellington and Wairarapa as the system makes its way over the North Island, Haddon said.
A large high is expected to come in early tomorrow which will clear any early showers away from Banks Peninsula, WeatherWatch has reported.
A few lingering showers may still affect northern Hawke's Bay and Gisborne.
Most of the country is set to be dry by Wednesday.