CLEVELAND, Ohio -- This year's St. Patrick's Day parade could become the largest in its 145-year history and, because it's on a Saturday, it could see record crowds of watchers.

When the parade is held on weekdays, the city requires a strict 1 to 3:30 p.m. window so that it doesn't run up against evening rush hour. But parade organizer Shannon Corcoran said rush hour is not a factor this March 17, so Cleveland's long green line down Superior Avenue can get even longer.

And it has -- 16,000 marchers and counting, compared with 12,000 last year.

One reason for the swell is 1,600 Boy Scouts celebrating 100 years of the Cleveland chapter of Boy Scouts of America. This year also marks 100 years of the national Girl Scouts of America, so 2,100 Girl Scouts, Brownies and Daisies will be marching.

Add the cops, firefighters, politicians, high school marching bands, labor unions, military veterans and Irish wolfhounds and you've got a big shebang.

"This is huge," said Corcoran. "This is a one-time-only that we'll ever have this many."

Normally, the parade, which steps off at 1:04 p.m. at East 18th Street and Superior Avenue, takes about two hours and 15 minutes to move along Superior to Public Square.

Corcoran hopes this year's version won't last longer than 21/2 hours.

Weekend parades, she said, usually draw more watchers, especially if the weather is good. Last year, on a weekday, it was 65 degrees and sunny, drawing an estimated 375,000 to 400,000 along the parade route.

The very early forecast for this year is 62 degrees and partly cloudy.

"If we have nice weather this year," said Corcoran, "we could easily see 400,000 plus."

Parade Executive Director Pat Murphy, who has been involved in the celebration's organization for 30 years, said weekend crowds are better behaved.

"I think it's because you've got more families coming down, rather than just a bunch of unsupervised kids," he said. "And this year, with the Boy Scouts and Girl Scouts, we'll likely see even more families."

Murphy said the parade organization put out a call for marchers and floats in September and began sending invitations in November. As of Tuesday, he said, the organization still had unprocessed requests and more were coming in.

"Here we are, 10 days out and people are still calling us to march in the parade," he said.