How many LA voters will show up at the polls on Election Day?

Roughly three-quarters of registered voters in Los Angeles County will cast a ballot this year for president, United States Senator and other races, if history is any guide. County turnout in the last three presidential elections was 71 percent in 2012, 82 percent in 2008 and 79 percent in 2004.

The main motivator is a nominee for president on the ballot, according to Jessica Levinson, a professor at Loyola Law School. Other factors that can boost turnout include exciting Senate races and ballot propositions. But she doesn't see any of those happening in 2016.

"I think all of those factors would indicate that we're not going to have record-breaking turnout this time," Levinson predicted.

She points to the presidential candidates as the culprit: "Unfortunately, what we have this cycle aren't two candidates that are exciting people. It's more of two presidential candidates that are turning people off."

Levinson thinks L.A. County turnout is unlikely to break 80 percent, as it did in 2008, and could fall short of 70 percent.

"We're on a historical downturn in terms of voter turnout," she noted.

General election turnout always tops the primary figure, and they often track one another. When primary turnout, seen in the blue, dipped in years like 1996 or 2008, then the orange line showing general election turnout followed suit.

If that trend holds for this year, turnout could get near the 70 percent mark set in 2012. About 42 percent of L.A. County voters cast ballots in June's primary, far ahead of the 22 percent primary mark four years earlier. Since 1940, the average jump from primary to general turnout has been about 26 percentage points.

In truth, we won't know where turnout lands until well after election day.

When polls close, we'll quickly see vote-by-mail and early-voting ballots counted. Next will come precinct totals. But other votes will take longer to count. Provisional ballots are scrutinized one at a time, and vote-by-mail ballots can show up as late as Nov. 11 and still be counted by the Registrar Recorder/County Clerk, as long as they're postmarked by Election Day.

The vote total won't be finalized until Dec. 6, when the county Board of Supervisors certifies the results.

This year, half a million ballots were processed in Los Angeles County after the date of the primary election. Keep that in mind as you hear about close races.

The statewide and regional picture

Statewide, a record number of Californians are registered to vote. The Secretary of State reported last week that 19.4 million people are registered, up from 18.2 million in 2012.

Those figures reflect half a million new L.A. County voters since 2012. But it's not clear yet how many of those voters will show up at the polls.

"Registration doesn't always equal voter turnout," Jessica Levinson said. She added that registration is a first, positive step in the political process even if it doesn't immediately translate into voting.

If many voters stay home, it wouldn't be the first time Southern Californians shrugged at the prospect of casting a ballot. In terms of political participation, the region could use a morale booster. Low turnout has been a storyline in many recent elections. And L.A. County's turnout in the 2016 primary was among the lowest in the state, in 54th place out of 58 counties.

It was also lower than turnout elsewhere in Southern California.

Note: The Secretary of State uses the registration totals 15 days before the election, while the registrar uses the figure from 29 days out, so the turnout percentages differ slightly.

Riverside and San Bernardino counties both edged out Los Angeles in turnout, but came in below the statewide turnout figure of 47.7 percent.

In Orange County, turnout fell just short of half of registered voters casting a ballot, at 49.6 percent.

Southern California's overachievers were Ventura and Santa Barbara counties, where 51.8 percent and 59 percent of voters cast primary ballots, respectively.