As of Monday morning, at least 40 percent of registered Oregon voters had returned ballots to their county elections offices ahead of Tuesday's general election.

That's a big jump from the previous statewide turnout estimate of 32 percent, which reflected ballots tallied as of the close of business Thursday.

The 8 percentage point jump reflects ballots tallied in each of Oregon's 36 counties Friday. But the bigger reason it increased so dramatically: Elections workers in the state's four most populous counties — Multnomah, Washington, Clackamas and Lane — toiled Saturday to process 10,000 (Lane) to 20,000 (Washington) ballots that reached their offices on Friday and Saturday.

Those counties lean Democratic, which probably helps explain why Democrats held a tiny edge in turnout rates, as tallied by the Oregon Elections Division at 8:30 a.m. Monday. According to that office, 49.3 percent of registered Democrats had returned ballots compared with 49.0 percent of Republicans.

Nationwide, voting has also surged at this point in the elections cycle. At least 28 states and the District of Columbia have already surpassed their total early-vote tally from the last midterms, University of Florida professor Michael McDonald told Bloomberg News. There was unusually high turnout in special and primary elections this year and that's continuing, he said. "People are engaged and voting in this election."

One has to be careful when looking at early voting, however. In many cases, it can just simply be a shift in timing by people who would otherwise head to the ballot box on Election Day. However, Bloomberg reports there are indications that this year's surge isn't just cannibalizing Tuesday voters, but instead bringing out new voters who wouldn't normally vote in a midterm election.

In Oregon, ballots must reach elections offices or official dropout boxes by 8 p.m. Tuesday in order to be counted.

The Oregonian/OregonLive, with the state's largest team of reporters, editors and results-gatherers, will bring you complete up-to-the minute results Tuesday starting at 8 p.m.

—Betsy Hammond