Could it get any worse? Snow and rain for sodden south

An aerial view of the flooding in Otago on July 22. Photo / Otago Regional Council

Hard-hit regions of the South Island have just days to prepare for yet another onslaught of wintry weather.

With vast tracts of farmland submerged by murky floodwater, hundreds forced out of their homes and slips spilling over roads and properties, another spell of bitterly cold weather is set to bear down on flood-ravaged southern regions just starting to recover from the weekend.

MetService has issued a severe weather outlook with snow expected to fall as low as 200m in Southland, Otago and Canterbury and even lower in the far south.

As well more rain is forecast for sodden eastern districts in a swift moving front that is expected to race up the South Island on Thursday.

Duty forecaster Tom Adams said while the amount of rain wasn't expected to come near the normal warning threshold it was being treated a little differently given the impact it would have on already saturated regions.

Said Adams: "If the weekend hadn't happened it would be just another rainy day but because of the saturated ground it's significant."

He said it looked like up to 40mm could fall overnight on Thursday and MetService and regional council officials were now discussing how best to handle the unfolding situation.

"At the moment we issue warnings for 100mm [of rain] but it's not looking likely to be anywhere near that but it won't take much to create problems," he said.

Any special warnings or watches would be issued closer to Thursday, he said.

Snow was likely to fall on higher parts of Dunedin, Adams said.

Weatherwatch.co.nz said while heavy rain looked focused on the west of the country there was a fairly high chance rain would set back into parts of Otago and Canterbury late on Thursday with a chance of heavy snow on alpine passes.

The brief cold snap would give way to a weekend of fine clear skies and icy cold nights.