Weather: Snow possible in lower South Island as front nears

Meteorologists are monitoring the possibility of "unseasonal snowfall" in the lower South Island late on Wednesday, as cold southwesterlies approach the region.

MetService forecaster Aidan Pyselman said a front would move up the South Island late tomorrow, with a deep low to the south of it.

"Then we have quite a reasonable southerly change and that's actually got quite a long stretch that goes way back down towards the Antarctic shelf.

"So there's going to be a pretty good river of cold air in behind that front during Wednesday."

It had the potential to bring a little bit of rain to drought-stricken Southland farmers and some snow down to about 800m-1000m late on Wednesday, and possibly some frosts later in the week.

"It's not usual for this time of year, but it's also not a given. We're keeping an eye on the situation."

At this stage, it was likely rainfall accumulations would meet warning criteria in Fiordland and Westland tomorrow and on Wednesday.

It was possible northwest gales could become severe for inland parts of Southland and Otago and the Canterbury high country to Marlborough tomorrow and on Wednesday.

It was also possible gale southwesterlies could become severe about coastal Otago on Wednesday and again on Friday, he said.