A MetService spokesman said a deep low and associated fronts were expected to move across the Tasman Sea during the weekend and bring heavy rain to the west of the South Island from tomorrow.
"Watches for heavy rain are now in place for Fiordland and Westland."
An active front was also expected to bring strong north-to-northwest winds to much of the South Island tomorrow and Monday.
He said it was possible north-to-northeast gales would become severe over coastal parts of Fiordland and southern Westland, and north-to-northwest gales could affect eastern Fiordland and inland Southland and Otago.
On Monday and Tuesday, strong and very cold westerlies were forecast to bring snow showers to quite low levels over southern New Zealand, he said.
"At this stage, snow amounts and wind speeds are not expected to meet warning criteria, but they could affect livestock and driving conditions.
"People are advised to keep up to date with the latest forecasts, as these watches may be upgraded to warnings, or other areas could be added."
MetService Road Snowfall Warnings for all New Zealand
Crown Range Road
Valid: 4 hours from 12.00pm Mon 11 Sep to 4.00pm Mon 11 Sep
Forecast: Light snow showers are possible above 800 metres during Monday afternoon, but little snow (if any) is expected to settle on the road.
Milford Road (SH94)
Valid: 26 hours from 10.00am Mon 11 Sep to 12.00pm Tue 12 Sep
Forecast: Snow is expected to affect the road late Monday morning and afternoon. Expect 2 to 4 cm to settle near Homer Tunnel, with lesser amounts down to 700 metres. Further snowfall is expected Monday night and during Tuesday morning and a further 10 to 20 cm of snow is expected near the tunnel with lesser amounts down to 600 metres.
