Rain is forecast in Philadelphia tomorrow, Election Day.

The question is: Will it rain Katz and dogs? Or float a boat for Street?

The answer is tricky because it depends in part on just how committed voters are to electing Republican Sam Katz or Democrat John Street their next mayor.

Experts say bad weather affects turnout, but it is more of a factor for voters who are less motivated to vote for a particular candidate.

"The more fervent your base of supporters, the less of a factor weather is," said Fred Voigt, executive director of the non-partisan political watchdog group, Committee of Seventy.

If voters are motivated and the interest level in an election is high, little short of a hurricane or blizzard will deter them from going to the polls, said Curtis Gans, director of the Washington-based Committee for the Study of the American Electorate.

Gans noted that voters stood in line at some polling places for as long as 21/2 hours in a steady downpour in Atlanta during the 1992 general election so they could vote for Bill Clinton.

Voters who are less likely to turn out in bad weather are so-called "soft voters," said Larry Ceisler, a Democratic political consultant, and he notes that both of the mayoral candidates have a degree of soft support.

Daily News pollster Terry Madonna, of the Center for Politics and Public Affairs at Millersville State University, said such voters, whom he calls "marginally interested," could determine the outcome in a close election.

Most pollsters, including Madonna, rate the contest between Katz and Street a tossup.

"The less interested people are to vote, the more likely they are to be influenced by external factors, like bad weather," Madonna said. "The question is, which candidate are these marginally interested voters more likely to vote for in this election?"

According to the Daily News/ Fox Philadelphia Keystone Poll released on Oct. 27, marginally interested voters - those who are likely to vote but not certain to vote - favor Street by 43-33. Voters who are certain to vote favor Katz by a 44-34.

That means Street stands to lose the most if tomorrow turns out soggy, right? Not necessarily.

"First, the weather would have to be really bad to have any measurable impact," Madonna said. "Second, a good field organization can mitigate the impact of bad weather on turnout by providing transportation that can whisk a voter from their front door to the polling place."

The forecasters say simply that rain is likely. Not a downpour. And Street is believed to have a better organized field army than Katz. So, who wins if it rains? It's a wash.