Stormy weather could complicate final get-out-the-vote efforts for both presidential campaigns on what is expected to be a rainy Election Day in key battleground states.

Weather forecasts in Pennsylvania, Virginia and North Carolina — all of them potential swing states in this year’s race — are predicting rain on Tuesday, according to the National Weather Service and The Weather Channel. Slightly lower chances of rain are predicted for the Western swing states of Nevada, Colorado and Montana.

Strategists and scholars have debated the effect of rain on voter participation, but if it does lower turnout Tuesday, forecasts favor Sen. John McCain (R-Ariz.) in Pennsylvania and Sen. Barack Obama (D-Ill.) in North Carolina, Colorado and Nevada, based on which precincts are likely to get wet.

In Pennsylvania, where Obama leads by 7.3 percentage points, according to RealClearPolitics’ average of major polls, a 70 percent chance of rain is predicted for the southeastern part of the state, which includes heavily Democratic Philadelphia. The rest of the state is likely to stay dry. If rain lowers turnout in Philadelphia, it could keep Obama supporters indoors.

North Carolina’s right-leaning coast looks to get the state’s worst weather, with 70 percent chance of rain forecast for the city of Wilmington. Meanwhile the Democratic precincts in the more Democratic-leaning Raleigh-Durham metro area have a 40 percent chance of rain. Obama and McCain are tied in North Carolina, according to RealClearPolitics’ average.

In conservative western Colorado and northern Nevada, 30 percent chances of rain and snow could also keep McCain supporters from the polls. In the smaller battleground of Montana, rain and snow in the western part of the state could favor McCain.

Obama leads in Colorado and Nevada, while McCain leads in Montana, according to major polls.

Forecasts for other battlegrounds, such as Virginia and Georgia, appear to favor neither candidate. Rain is forecast at 30 percent for the southeast portion of Virginia, which is home to both conservative and liberal districts. Conservative central Virginia and the balanced D.C. suburbs are expected to stay dry.

Georgia, which voted statewide for President Bush in 2000 and 2004, is predicted to see rain in the Savannah area.

The effect of weather on voter participation has been long debated by political strategists. A 2007 study by researchers at the Universities of Georgia, Pittsburgh and California found that rain lowers turnout by 1 percent per inch of rain, and that it helps Republicans more often than Democrats.

Researchers Brad Gomez, Thomas Hansford and George Krauses studied turnout information and more than 22,000 weather reports and found that every inch of rain beyond average Election Day levels benefited the GOP presidential candidate by an extra 2.5 percent of the vote.

Gomez suggests that, according to traditional turnout models, registered Democrats are more likely to be “peripheral” voters, less engaged in the political process than Republicans. Others have speculated that, since a larger percentage of Democratic voters are poor and do not own cars, Democrats are less likely to walk or take public transit to polling places and vote.