The Upshot will adjust vote tallies in real time:
More sophisticated analysts interpret leads through the lens of the outstanding votes. “There’s a lot of votes left to be counted in heavily Democratic Cuyahoga County,” Jeff Greenfield said on CNN in 2004. “Remember, some of the votes outstanding are down here in Marion County where Obama is winning,” John King said on the same network in 2008.
This year, The Upshot will aim to let you be your own John King. In about a dozen of the closest Senate races, we, like many others, will track the leads reported by The Associated Press. But we will also adjust those leads based on what we know about where the votes have come from. Our adjusted leads will be based solely on current and historical returns. They will not use data from exit polls, or any forecasts from Senate models. You’ll be able to find a link to the tracker on The Times’s midterm page and The Upshot’s home page.
Nate Cohn also has an extremely helpful primer on how the votes will come in in various states. On the Colorado race:
Our first real sense of where the night is heading might come just after 9 p.m., when the polls close in Colorado. Many counties will quickly count a significant number of mail-in votes, and these ballots will be fairly representative of the overall count. If one side is going to win by a few points, we could have a good idea by 10. But if you are thinking you’ll be able to go to bed then, put the pillow away. When the race in Colorado looks to be within one or two points, the networks might not even dare make a call until the next day. Despite the state’s fast start, just 80 percent of the vote was counted by midnight in 2012, and only 90 percent by 6 a.m. In 2010, Senator Michael Bennet’s 1.4-point victory wasn’t called until the next day.
And on Iowa:
The single most dramatic contest of the night might be Iowa. The first returns will disproportionately include Democratic-leaning early ballots, and Bruce Braley could hold a lead for hours even if Joni Ernst goes on to win by a slight margin. Eighty percent of the vote won’t be counted until midnight; a projection probably won’t come earlier unless Ms. Ernst wins by a clear margin.