Think you'll know who won on Election Night? Not so fast . . .

If you plan to stay awake on Election Night until you know the outcome of every race - or even until you know who controls the House and Senate - you may need to buy a lot more coffee.

An unusual number of key races are expected to be nail-biters, which often take a while to sort out. Quirky rules and procedures may prolong other races. And you can be sure that somewhere on Nov. 6, something that never happens will occur - and will delay the count in some unlucky jurisdiction.

Here are some ways Election Day could turn into Election Week, Election Month or longer.

• Some states count slowly: Sometimes, it's the scale. Hundreds of thousands of votes take longer to tally than just a few, so huge urban areas often lag behind smaller places.

Other times, it's the mail. California, for instance, where there are seven tight House races, is notoriously slow, in part because more than half of voters opt to use vote-by-mail ballots (a.k.a. "absentee" ballots in some places). California ballots postmarked on Election Day have three days to show up at county elections offices. A few other states allow a week or 10 days; Alaska will accept ballots from abroad up to 15 days later.

"I've always speculated about a worst-case scenario where an Alaska Senate seat could determine control of the U.S. Senate, and there may still be ballots sitting at local 'post offices,'" said Paul Gronke, director of the Early Voting Information Center at Reed College, in an email. "Post office," he said, could actually mean a remote bait shop or grocery store from which ballots would need to be airlifted, validated and counted.

Gronke said some jurisdictions that depend heavily on mail-in voting get quicker results by processing the ballots as they arrive rather than saving all the envelope-opening, signature-validating, scanning and such until after the polls close. That way, they just need to hit the button to count the ballots.

Traffic could be a factor, too. A few jurisdictions do "central counting," where all ballots are delivered to a single location after the polls close to be counted all at once. One of those is massive Los Angeles County, where some votes arrive by helicopter and boat.

"It's like a scene out of 'M.A.S.H,'" said Doug Chapin, an elections expert and adjunct professor of election administration at the University of Minnesota. "The choppers land and people run in and unload the ballots and then load in empty boxes, and the chopper goes back out to get more."

Caution plays a role as well. When races are close, elections officials may wait to release information until they're confident that their "unofficial" results are nevertheless pretty accurate, Chapin said. It's a pressure-filled balancing act. In 2010, a longtime Riverside County, Calif., registrar was fired over a slow count.

• Random glitches cause delays: Snowstorms strike. Voting machines break down. Squirrels knock out power. "There's always going to be one place at least that just has a bad day," Chapin said. "There are so many ballots being counted in so many jurisdictions in so many different ways, that something is going to go wrong. Even if nobody does anything wrong, something is going to go wrong."

That may lead courts to order that polling places be kept open later, which slows counting on top of the original problem.

Also, more states are switching from touchscreen machines, which are widely considered to be less secure, to paper ballots with optical scanners, which take a little longer to process.

• Runoffs may be required: In most races, the person who gets the most votes wins. But the winner of certain races in a few states must also get 50 percent of the vote. If no one does, the top two vote-getters compete later in a runoff.

One of those races is Mississippi's special Senate election, where four candidates are vying to serve out the term of Thad Cochran, a Republican who resigned in April for health reasons. The runoff, which is considered to be very likely, would be Nov. 27.

Another is the Georgia governor's race, where Democrat Stacy Abrams and Republican Brian Kemp are running neck-and-neck. Libertarian candidate Ted Metz could siphon off just enough votes to keep Abrams and Kemp under 50 percent and trigger a Dec. 10 runoff.

Louisiana has no pre-election primaries to cull the herd of candidates, and each of its six House races has between three and seven names on the ballot. Any needed runoffs will be Dec. 8.

And then there's Maine's House and Senate races, where the "ranked-choice voting" ballot has a built-in runoff. Instead of voters choosing just one candidate in a race, they can rank all the candidates in order of preference. If no candidate gets more than half of first-place votes, all ballots will be trucked to Augusta for re-sorting.

First, elections officials will eliminate the candidate who got the fewest first-place votes. If you voted for that candidate, your vote will instead go to the candidate you ranked second. This continues, round by round, until someone gets a majority.

Confused? The state made an animated explanatory video that includes the fantastic sentence, "In this example, the skipped ranking will be ignored, and Spider-Man will be counted as your second choice."

• Provisional ballots could come into play: If you go to the polls and run into a problem - say your name isn't on the registrar's list, or you forgot to bring your ID - federal law requires most states to let you cast a provisional ballot. (A few states that have same-day voter registration are exempt because you can register instantly.) Later, county election officials review those ballots and resolve the issues.

Not enough provisional ballots are cast to affect the final outcome of most elections, but they can delay results of a very close race.

And recently, several states, most notably Georgia, tightened voter ID laws and purged a large number of people who hadn't voted recently from the rolls, which could mean more people cast provisional ballots than usual.

• Someone can demand a recount: In some places and for some races, recounts are automatic if the winning margin is below a certain percentage. In other places, a candidate (or even some other person) can request one.

Either way, the process can be excruciating.

The longest contested election in Senate history was for an open New Hampshire seat in 1974. After an initial count showed Lewis Wyman, R, beat John Durkin, D, by 355 votes, a recount showed Durkin won by 10 votes. Then a re-recount came up with Wyman winning by two votes. A re-re-recount was done by the Senate itself - and ended with no resolution.

Finally, the candidates gave up and agreed to a do-over, and Durkin won a special election the following September.

• Lawyers could get involved: Gerrymandering. Perceived voter suppression. Lost ballots. Hacking.

Plenty of issues have the potential to cause a tight election to go into overtime in the courts.

"All of the skirmishes we're seeing now have the potential to reemerge or ramp up after Election Day if they seem to have had an impact on the outcome," Chapin said.

Unlike a recount, which simply seeks a new tally, a post-election legal challenge alleges that the count wasn't accurate for some reason and doesn't represent the true result. (This is also called "contesting" the election.)

In 2008, the race between incumbent Minnesota Sen. Norm Coleman, a Republican and challenger Al Franken, a Democrat, was so close - 206 votes - that it triggered an automatic recount, then a legal challenge by Coleman based on how absentee ballots were counted (or not), then an appeal to the Minnesota Supreme Court. Franken was finally declared the winner nearly eight months after Election Day.

All of these scenarios cause heartburn for elections officials who'd much prefer smooth-running contests with clear winners whose victory speeches are finished by bedtime.

"The election administrator's prayer," Chapin said, "is, 'Let the margins be wide.'"

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