The Milford Road (State Highway 94) closed from East Gate (Hollyford) to Donne River (Westgate) at 5pm and was likely to reopen tomorrow morning after a road inspection.
Milford Road Alliance manager Kevin Thompson said there was low cloud and rain today, and thunderstorms were likely in the Homer Tunnel area tonight.
The unsettled spring weather was expected to bring heavy rain, thunderstorms and snow over the next few days - conditions that heightened the risk of avalanche.
"Warm, heavy rain onto our high level snow fields increases the likelihood of a larger natural avalanche," Mr Thompson said.
"While we have been seeing small natural avalanches in the last month, it is only in the last week we have had enough snow arrive to affect the road."
The avalanche hazard risk was increased from low to moderate at 5pm today.
Milford Road Alliance said it was "highly possible" that SH94 would close again on Thursday evening due to predicted snow to the road overnight.
More heavy rain and snow was forecast for the rest of the week.
Forecast for the Homer Tunnel area
Today: Showers turning to rain with heavy falls later.
Thursday: Periods of rain, with snow developing.
Friday: Morning snow showers about the tunnel easing.
Saturday: Morning rain, with heavy falls, followed by a few showers.
Sunday: Early rain with possible snow about the tunnel.
