CHICAGO (CBS) — Polls have opened in Illinois as voters prepare to cast ballots in the primary election for governor, U.S. Senator, and many other races.

The polls opened at 6 a.m., and will stay open until 7 p.m. In the Chicago area, the forecast calls for one of the warmer days so far this year, with a high of about 52 degrees. There will be only a minor chance of rain late Tuesday afternoon.

Election authorities weren’t making predictions, but voter registration and early voting trends suggest low turnout, likely less than 20 percent.

The biggest races in Tuesday’s primary are on Republican ballots, starting with the GOP race for governor. Billionaire venture capitalist Bruce Rauner is the frontrunner against state senators Kirk Dillard and Bill Brady and Illinois Treasurer Dan Rutherford.

In the Republican race for U.S. Senate, state Sen. Jim Oberweis is facing off against businessman Doug Truax. Oberweis has been leading in pre-election polls, but his campaign came under fire recently after he spent several days vacationing in Florida less than a week before the primary. Oberweis has said he was fulfilling a promise to his wife to spend her birthday in Florida, but Truax has said the trip shows he’s out of touch with voters.

On Democratic ballots, most of the statewide races are uncontested, and Gov. Pat Quinn faces only political novice Tio Hardiman, and Quinn is expected to win easily against his underfunded challenger.

Voters can only cast a ballot for one party on Tuesday.

In Chicago and suburban Cook County, election officials should be able to confirm voter registration much quicker than in the past, after replacing old bulky books of voter signatures with tablet computers to confirm a voter’s signature. Election officials said it should help speed up the voting process.