It's anyone's guess who will show up to the ballot box on Tuesday.

Mark Goins, Tennessee's coordinator of elections, knows there's somewhat of a formula to follow.

You can look at spending in the main races, totals that have exceeded any other year on record. You consider the weather forecast for Election Day — which, on Tuesday, is expected to include storms.

But the early voting numbers are perhaps the most telling, and this year in the Volunteer State, they're record-setting.

"We are telling counties: 'Be ready,'" Goins said. "We expect that we're going to have a historic midterm election."

In two weeks of early voting, which ended Thursday, voters in the state have cast almost as many ballots as they did in the entire 2014 midterm election.

On Friday, the Secretary of State's office announced 1,378,840 people had voted early, just 50,000 fewer than the total in the last midterm.

Tuesday, Goins expects nearly as many more voters to turn out.

Elections officials comparing 2018 midterm to 2016 turnout

At almost every early voting polling place in Davidson County on Thursday evening, there was still a line when polls closed at 7 p.m, according to Goins.

"I think the last person voted around 10 o'clock," he said, describing the long lines as abnormal for midterms.

"We have had lines before in early voting," he said. "But I don’t ever recall having that large of lines at that time."

The early voting turnout has been so high this election, Goins said, that elections officials have shifted to comparing numbers to the 2016 presidential election rather than the 2014 midterm.

On the ballot in the state are two open races — elections for both governor and U.S. Senate —in addition to three congressional races.

U.S. Rep. Marsha Blackburn, the Republican nominee, is up against former Democratic Gov. Phil Bredesen for the seat held by retiring Sen. Bob Corker, a Republican.

Bill Lee, a businessman, is the Republican nominee running against former Nashville Mayor Karl Dean, a Democrat, for governor. Republican Gov. Bill Haslam is finishing his second term in office.

The last time two open competitive statewide races have appeared on the ballot in Tennessee was 2006.

More:What time can I vote on Election Day in Tennessee?

Compared to 2014 — when incumbents Haslam and U.S. Sen. Lamar Alexander were up for re-election — there has been a 119 percent increase in early voting totals, or more than twice as many voters.

Early turnout in the 2016 election is just 18 percent higher than this year.

Williamson County has seen the highest level of turnout, as 50 percent of registered voters have already cast ballots, followed by Loudon, Wilson, Rutherford and Davidson counties.

In addition to leading voter turnout this election, Williamson County has seen more of an increase — 182 percent — than any other county compared to 2014 early voting numbers.

Shelby County's early voting increase over 2014 turnout was 123 percent, while Knox County's was 106 percent higher.

Reach Natalie Allison at nallison@tennessean.com. Follow her on Twitter at @natalie_allison.