As pundits furiously analyze last-minute ground organization, media buys, and legal challenges, there is one factor that no campaign can control: inclement weather, which, as Nate Silver pointed out yesterday, can lower turnout so dramatically as to swing an election, as it did in 2000 and 1960. According to a 2007 study in the Journal of Politics, "for every one-inch increase in rain above its election day normal, the Republican presidential candidate received approximately an extra 2.5 percent of the vote."
So how could weather alter the voting results in battleground states this year? Today we'll look at Pennsylvania, where Obama is leading by 10.8 points. Using the Journal of Politics' metric, for McCain to close the Bush-Kerry margin in Philadelphia County, there would need to be 24 inches of rain--unlikely given that next Tuesday there is only a 10 percent chance of precipitation and the November average precipitation in Philly, for the entire month, is 3.16 inches.
But what about a more rural area, like Bucks County, which Kerry won by only 3 percent in 2004 and where Politico has Obama up by the same slim percentage? The forecast for next Tuesday there is pretty similar to that of Philly, with a 10 percent chance of precipitation but with a slightly higher average precipitation for November at 3.85 inches. So in this case, precipitation could actually make a difference; even if there was only an inch of rain, the gap would diminish greatly.
But in a year where Democrats' current enthusiasm far outweighs that of the Republicans, inclement weather could actually hurt Republicans more than Democrats. Yesterday morning, for example, when both candidates were in the Keystone state, Obama still managed to attract 9,000 people to an outdoor rally in the rain at Widener University in Chester, as compared to McCain's crowd of less than 5,000.
The Obama campaign doesn't seem to be worried. Zach Friend, the PA press secretary, told me yesterday: "As for the weather, we're simply telling people to bring comfortable shoes, a warm coat, and even some coffee. Pennsylvanians are excited for change. The lines may be long and the weather might be rough but we've waited eight years for this--and we can wait a few minutes more to put this country back on the right track."
While we'll have to wait and see what effect--if any--the weather has in Pennsylvania next week, the Plank will continue keep you posted this week on weather updates in the key battleground states.