The world number three played nine holes at Augusta National before it was closed in the early afternoon.
World number three Day played nine holes at Augusta National, his fourth consecutive day on the fabled course, before it was closed in the early afternoon when the area fell under a tornado warning.
Day withdrew from the World Golf Championships Match-Play event two weeks ago to be with his mother, Dening, as she faced cancer surgery. Her uncertain prognosis through chemotherapy kept his status in doubt for the Masters.
But Day said Monday that his mother is improving and she might even be at the course on the weekend to watch him compete for the green jacket.
"She's good," Day said. "She had the left quarter of her lung taken out... I was with her pretty much every day back home. She is in a fair amount of pain but hopefully things are looking up."
A severe thunderstorm closed the course for more than an hour and forced evacuation of the course even before the tornado warning shut down the course the remainder of the day.
Heavy rains and strong thunderstorms are expected again on Wednesday on the eve of the opening round, which could soften the greens and lead to more showers for early starters Thursday.
After that, the forecast is for dry conditions at Augusta National, where weather has not suspended play since the third round in 2008 and not postponed a round since the opening round in 2003.
Even if greens and fairways are more receptive, it's likely the lightning-fast trademark putting surfaces will be back at full speed for Sunday's final round.
"You've got to hit the shots in the right spots," warns world number one Dustin Johnson.
Among the newcomers hoping to become the first Masters debutante to take a green jacket since Fuzzy Zoeller in 1979 is Spain's Jon Rahm, who won his first PGA crown in January at Torrey Pines.
"A guy like Jon Rahm, obviously he has been playing great golf. I don't see any reason why he can't go and play well or be in contention this week and have a chance to win," said eighth-ranked Rickie Fowler.
"It's not a golf course that you have to be any certain type of player. He's shown that he can play and compete with the best. He has already won. So it will just be him going out and learning this golf course for himself."
One of the crucial areas to master is Amen Corner -- the noted par-4 11th, par-3 12th and par-5 13th holes. Jordan Spieth was on his way to defending his title in Sunday's final round last year only to find a watery grave twice into Rae's Creek and take a quadruple bogey at 12, helping England's Danny Willett take the title.
"Yeah, it's a really good stretch of golf especially with the way the forecast is looking for Thursday and Friday," said 2016 PGA Championship winner Jimmy Walker.
"The winds look like they're going to pretty gnarly, and that's a section of the course that gets really tough, especially if the wind swirls. You get through there even par, you're doing really well against the field.
Seventh-ranked Justin Thomas says level par through the three-hole stretch is his goal too.
"If I went through those even each day, I probably wouldn't be complaining too much," he said.