The road opened shortly before 1pm.
NZTA regional transport manager Mark Owen said they placed teams on the hill during the night, but the road was being hit with passing snow showers, which undid the clearing work.
The MetService had been "quite reliable" with snow predictions, including a last shower at noon.
"We want to make sure the road is safe, we've got to take care of all road users."
Snow in low-lying areas was particularly notable on the flats near Masterton and to the north, with heavy snow showers reported near Mt Bruce.
Mr Owen said they were monitoring conditions there, with Mt Bruce being a greater transport priority than Rimutaka.
Masterton police senior sergeant Mike Sutton said there were no reports of vehicles in any difficulty yesterday.
However, the Times-Age team, heading to Mauriceville School, had to be towed out of snow and mud after pulling over for the photographer to take pictures.
Mauriceville School's grounds turned white, delighting the morning classes and prompting some to create miniature snowmen, before rain washed the snow away.
Snow warnings were lifted for Masterton and south at 3.20pm yesterday.
Today is expected to be warmer (9 degrees) with showers clearing in the afternoon and southwesterlies easing.
Thursday is predicted to be fine and 13 degrees.
But with a calm, clear day, Mr Owen is warning Thursday carries a risk of black ice on Rimutaka Hill Rd and Mt Bruce.
