(CNN) -- Presidential candidates have been wooing voters in Iowa for months, but who wins Thursday may simply come down to where the caucus-goers live, where they meet and the weather.
Iowa is a mixed bag politically, and one of the most evenly divided states in the nation. But the candidates will likely watch two regions more closely than others.
The central part of the state -- including industrial Des Moines -- is Iowa's most Democratic area.
Western Iowa, on the other hand, is home to the most Republicans -- especially the rural counties in the northwest.
The Mississippi River city of Davenport is expected to be one of the most significant battlegrounds, with Linn County -- dominated by the university town of Cedar Rapids -- also attracting lots of attention from both parties.
Past Iowa caucuses have been nail-biters for the candidates.
Democrat Al Gore won the state by a margin of just 0.3 percent in 2000, while President Bush carried it in 2004 by 0.7 percent. In fact, Bush was the first GOP presidential candidate to carry Iowa in 20 years.
The support of Iowa's largest newspaper, the Des Moines Register, may also play a role in Thursday's caucuses. The paper's presidential endorsements began in 1988 and have become a highly sought-after prize in Iowa presidential politics.
George W. Bush was the Register's pick in 2000 and went on to win Iowa, the GOP nomination and the White House. Republican presidential hopeful Bob Dole won the state in 1996 and 1988 after receiving the paper's support.
Democratic candidates haven't had as much success with the Register's endorsement. John Edwards finished in second place in Iowa in 2004, while Paul Simon was also a close second in 1988.
The paper endorsed Sen. John McCain and Sen. Hillary Clinton for their respective parties' nominations.
The candidates have to appeal to voters with strong opinions.
On the Republican side, 37 percent of participants in the 2000 Iowa GOP caucuses identified themselves as members of the religious right and 73 percent described themselves as conservatives.
Meanwhile, 56 percent of the participants in Iowa's 2004 Democratic caucuses described themselves as either very or somewhat liberal. About 37 percent said they were moderates.
Iowans who take part in the caucuses must traditionally brave freezing temperatures and lots of snow.
Presidential candidates know bad weather may affect how many people turn out, but 1972 was the only time rough winter conditions played a role in the caucuses, according to Drake University's Hugh Winebrenner -- the nation's leading expert on Iowa caucus history.
Caucus-goers that year encountered heavy snowdrifts from a blizzard the previous day.
Temperatures dipped below zero across most of the state. The weather forced about one-fourth of Iowa's 99 counties to postpone their Democratic caucuses up to two days after the scheduled date.
The forecast for Thursday is much better. Temperatures will be in the 20s during the day and dip just below that as the caucuses begin, according to the Des Moines Register. E-mail to a friend