NEW ORLEANS—Parades managed to roll Sunday despite inclement weather, but Monday's Lundi Gras celebrations may not be so lucky.

Lundi Gras—Fat Monday—includes the final festivities before Mardi Gras. Forecasters say rain threatens Monday's parade of the Krewe of Orpheus, the star-studded group led by entertainer Harry Connick Jr.

And Fat Tuesday could be a wet one: The National Weather Service forecasts rain for much of the day, when traditionally as many as 1 million people revel in the streets.

Wars and even a police strike have prevented Fat Tuesday parades from rolling several times, but only once—in 1933—has foul weather led to the cancellation of the Rex parade, according to Mardi Gras historian Arthur Hardy. Rex's parading history dates back to 1872.

"It's not looking good, but we're still hoping," Hardy said of Tuesday's forecast. "Winds are much more damaging than rain. That's the ultimate concern."

Hardy said it would be a "mighty sad day" if stormy weather nixed the big Mardi Gras parades this year.

City officials have the ultimate authority to decide whether a parade will roll.

"But it's always done in cooperation with the (krewe's) captain," he added.

If parades on Tuesday are canceled they would not be rescheduled. Lent begins on Wednesday. Mardi Gras is the festival that leads to the solemn season.

The inclement weather and a shooting Saturday night on Bourbon Street didn't appear to dampen the spirits of visitors.

Lisa Preston of Charlotte, N.C., said she was determined to enjoy her first Mardi Gras in New Orleans.

"I'm having a blast," she said, sporting a purple top hat and neck full of beads. "After the shooting, I'm keeping my eyes open, but Mardi Gras has really been a lot of fun, and the food. Oh my goodness, the gumbo here is out of this world."

Monday's festivities include the traditional meeting of the kings of the Rex and Zulu, which was to take place on the Mississippi riverfront in the late afternoon.

Orpheus is scheduled to roll at 6 p.m., with celebrity riders Connick, actor Gary Sinise and New Orleans musician Troy "Trombone Shorty" Andrews.

Others who were scheduled to ride in Orpheus Monday evening were Emmy and Golden Globe winning actress Mariska Hargitay, the Imagination Movers, a New Orleans-based rock band for kids, and Animal Planet's Tillman, the skateboarding bulldog.

Carnival season culminates Tuesday with the Rex and Zulu parades. So far, they haven't canceled parade plans.

Monday's Orpheus marks its 20th anniversary, and the parade will include more than 30 ornately-decorated floats, some designed to reflect parade themes of the past. The krewe was co-founded in 1993 by Connick and Sonny Borey, captain of the 1,200-member organization.

At the ball that follows the parade, Borey said Connick would be performing an original song he wrote for the anniversary, called "Smokey Mary Boogie Woogie Choo Choo Train." The song is on Connick's new album of Carnival music, titled "Smokey Mary," which was released this month.

Sinise, who stars in the CBS crime drama "CSI: NY," was scheduled to perform at the ball with his Lt. Dan Band—named after the character he played in the 1994 film "Forrest Gump," which also starred Tom Hanks.