US presidential election turnout could be affected by 3,000 km band of rain and stormy weather

In a country where voting is not compulsory and the margin of victory is small, weather has the potential to influence election results.

Research has shown that good weather in 1960 helped Democrat John F Kennedy, while rain in 2000 helped secure Florida and an eventual victory for Republican George W Bush.

This year’s race for the White House between Donald Trump and Kamala Harris is a classic case where the atmosphere could be the deciding factor, with a 3,000 kilometer band of heavy rain and thunderstorms forming from Texas to Canada predicted that will bring a stretch of severe weather over the next 48 hours to several states.

Professor Benjamin Reilly, senior non-resident research fellow at the University of Sydney’s Center for United States Studies, said the contest between the candidates was one of the tightest in US election history.

“It’s too close to call. Opinion polls put it very close,” he said.

Rosalind Dixon, law professor and director of the Gilbert + Tobin Center for Public Law at the University of NSW, said the race was “extremely close”.

“I think all the polls suggest it comes down to a few states, most of which are within the margin of error,” she said.

Professor Reilly said that while the severe wet weather would “adversely affect” turnout, it was too difficult to determine how significant the impact would be for the current election.

So could weather make a difference? During periods of inclement weather, such as rain or snow, turnout is affected for fringe voters who are less politically active.

And since people on the fringes of politics are more likely to be working class, the drop in voter turnout is greater for one party than another.

Two swing states could be affected by weather

Even without the backdrop of a US election, the current weather system is newsworthy.

A very moist air current from the Gulf of Mexico is feeding into a low pressure system over the central US.

This system is already causing severe weather with excessive rainfall and strong thunderstorms across much of the south-central US on Monday, leading to areas of flooding.

This low is slowly moving east and will extend a band of rain and thunderstorms from Canada to Texas on Tuesday (US time).

The heaviest rain is likely to fall on relatively safe states, including the Republican-leaning South and Democratic-leaning Illinois.

However, up to 50 millimeters is also possible in the critical swing states of Wisconsin and Michigan.

Professor Dixon said these two states were the ones to “watch” for this reason.

While Detroit is expected to remain east of the main rain band, northern Michigan and southern Wisconsin, including Milwaukee, are likely covered by the rain band for most of Tuesday’s voting hours.

How a rainy day affects turnout

Several studies look at the influence of weather on elections around the world and the results are clear – rain and snow have a significant impact on voter turnout.

A 2023 study of the Danish election showed that rainfall decreased turnout by 1% at 10 mm.

A 2007 The study looked at US elections and found that compared to normal conditions, rain reduces voter turnout at a rate of just less than 1 percent per inch or 1 percent at 25mm.

That could mean a 2% drop in participation in Michigan, Wisconsin and other counties hit by the heaviest falls (and even more in states farther south, where 100mm is possible).

A separate weather system dumping snow in Montana is also likely to dampen voter turnout, but is unlikely to prevent a sure win for Trump.

Republicans are no longer praying for rain

So does rain or snow favor one party over another? The old saying “Republicans should pray for rain” proved correct during the last US election.

As the theory went, bad weather may be the last straw for outlying voters, especially young people who haven’t developed a voting habit and were disproportionately inclined to support the Democratic candidate.

This link was tested in the Gomez study, and the data indicated that for every 25 mm increase in rainfall, the Republican presidential candidate received just over 2% of the vote—easily enough to swing a state and therefore an entire elections.

Professor Reilly said that because the generally heavily Republican states in the South – Texas, Oklahoma and Arkansas – would be hardest hit by the rainband, it would have an impact on the overall vote share for the party.

However, going by academic studies, including Gomez’s study, Professor Reilly said the Republican Party had been “speculated” to benefit more from the historically bad weather.

Professor Dixon said he suspected the weather would have “a very modest impact”.

“If you’re asking me to bet on it, I’d say it’s not going to turn out to be significant. Could it be? Absolutely,” she said.

Professor Dixon said the “more determined” and “politically engaged” voters would turn out regardless of the weather.

“There are certainly motivated voters on both sides, and I think it’s very relevant to say that the weather is a factor and we should be careful.

“But I think it’s very ill-advised to make firm predictions about how it’s going to go down.”

Indeed, the weather may have contributed to two electoral college results in the past.

In the closely contested 1960 election, very rainy or snowy weather is estimated to have given Richard Nixon an extra 106 electoral college votes over John F Kennedy.

The reverse results—if it was dry, not wet, revealed two situations that would have changed the outcome of an Electoral College—Bill Clinton won North Carolina in 1992 and Al Gore won Florida in 2000.

The latter change would have swung the incredibly close election of 2000 in favor of Mr. Gore to George W. Bush.

However, recent evidence suggests that this pattern may have reversed, as working-class voters now lean more toward the Republican Party and college-educated voters toward the Democrats.

A paper by Spencer Goidel and co-authors in 2023 showed the change in voter turnout by studying US federal elections from 2010 to 2020.

“Our findings show that increased voter turnout largely benefits the Democratic Party in the pre-Trump era. However, this pattern has changed drastically. In 2016, 2018, and 2020, the Democratic Party sees a much smaller gain in vote share as simulated turnout. increases, but also a large vote share advantage when turnout is extremely low.”

That implies Mr. Trump should probably be praying for sunshine rather than rain over Michigan and Wisconsin on Tuesday.