By Julian Linden

AUGUSTA, Georgia (Reuters) - If the early weather forecasts are right, golf's old brigade will have their work cut out winning this year's Masters, according to three-time champion Phil Mickelson.

The 41-year-old American fears forecasted thunderstorms will turn the year's first major into a lottery that could favor the more inexperienced players.

Mickelson said the rain would soften up Augusta National's notoriously fast and tricky greens, making putting easier and allowing players to shoot straight at the pin.

"You don't have to fear the greens and you don't have to know where the ball will end up and you don't have to fear certain shots because you can get up and down from the edges. Those shots are not as hard.

"Therefore, I think there's a very good chance that a young player, inexperienced, fearless player that attacks this golf course can win if you don't need to show it the proper respect."

Mickelson has been one of the few players who has thrived on the super-slick putting surfaces at Augusta National, winning the green jacket in 2004, 2006 and 2010.

He comes to the April 5-8 event in great form after winning the Pebble Beach National Pro-Am in February and with genuine hopes of winning the Masters if Mother Nature co-operates.

But the left-hander fears the advantage he has built up over his rivals on the faster greens could be washed away.

The course was left drenched Tuesday after overnight showers and the forecast for Thursday and Friday, the first two days of the event, is worse as thunderstorms are expected.

"If it plays like this, then there won't be the big mistakes made by any of the young players. I think that it will be a crowded leaderboard and a big birdie feast," said Mickelson.

"If there's some firmness that comes out and the green speeds get a little bit quicker and get a little bit firmer, I think we will see some of the young players make some mistakes that will cost them the tournament and the experienced players who position the ball properly and vary their risk/reward shot making, I think they will have an easier time staying on top of the leaderboard."

Mickelson would not say who he thought would win the event, saying dozens of players had a chance, but does expect Northern Ireland's Rory McIlroy to be a perennial contender.

"He plays without fear, which is a great way to play. When you get soft conditions like at the U.S. Open, he's going to light it up," said Mickelson.

"And I think that he's going to continue his great play and if he ends up, if he ends up learning this golf course, I think he's going to win here a number of times."

(Editing by Frank Pingue)