Soaking South: How does weather affect elections?

For most of the South, it's a rainy Election Day. According to The Weather Channel, Floridians can expect "scattered thunderstorms" and central/mid-Atlantic states are in for a "good soaking."

The media and pundits all agree that weather is bad for voter turnout and can impact tight elections. But just how much of a factor is it?

According to an exhaustive study of election data released last year, the answer is "potentially a lot." And historically, it's been Democratic Party candidates that have suffered the most from bad weather.

As political scientists Brad Gomez and Thomas Hansford (University of South Carolina) and George Krause (University of Pittsburgh) argue in the abstract of their report, "The Effect of Bad Weather on Voter Turnout and Partisan Vote Share in U.S. Presidential Elections, 1948-2000" (PDF):

The relationship between bad weather and lower levels of voter turnout is widely espoused by media, political practitioners, and, perhaps, even political scientists. Yet, there is virtually no solid empirical evidence linking bad weather to voter participation. This paper provides an extensive empirical test of this claim [...].

We examine the effect of weather on voter turnout in fourteen U.S. presidential elections (1948-2000). We employ meteorological data drawn from over 22,000 U.S. weather stations and GIS interpolations, providing us with data for each of the roughly 3000 U.S. counties during these elections.

We find that rain significantly reduces voter participation at the polls by a rate just under one percent per inch. Snowfall also decreases turnout, but only in rural counties. Moreover, we show that the estimated number of voters lost due to precipitation significantly benefits the Republican Party's vote share and GOP incumbents particularly.

We also show that weather may have been a determinative factor in at least one Electoral College outcome, the 1960 presidential election.

One interesting twist: some studies suggest (pdf) that, in a reversal of previous decades, in recent years Republicans have benefited most from higher turnout. So today's rain will clearly impact some races -- but it's not clear which party that helps.