Experts explain the week to come: Expect lead changes as mail votes are counted

In 2016, the call came at 2:40 Wednesday morning, just under eight hours after the first polls closed.

"The Fox News decision desk has called Pennsylvania for Donald Trump," Brett Baier reported to viewers on Fox News Channel. "This means Donald Trump will be the 45th president."

In 2012, the call came at just after 11 Tuesday night and Brett Baier again reported the outcome.

"Our decision desk is saying they are confident that we are projecting Ohio for President Obama," Baier said.

MORE: President Trump, Joe Biden making final push for Florida on Election Day Eve

But those declarative moments may not come Tuesday, not just because the battleground states are close, but because we won't even know how close they are.

For instance, in critical Pennsylvania, officials can't start counting mail votes until 7 a.m. on Election Day. Some counties don't expect to be done even by the end of the week.

In Wisconsin, counting may not be done until late Wednesday morning.

Officials in Michigan predict counting won't be done until Friday.

During those days, expect lead changes in all three of those states.

"It doesn't mean that anything is wrong with the system," said political science professor at the University of Central Florida, Dr. Aubrey Jewett. "It doesn't mean anybody is cheating. It just means it is taking a long time to count all these votes."

But if you're eager to start reading tea leaves, keep an eye on the four states that are allowed to start counting before Election Day: Arizona, Georgia, North Carolina and Florida.

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All of their results won't be in right away, but we will likely know if we are headed for a landslide or a barnburner.

"Once we get an idea of which way those states are going, and we will by late Tuesday night, even though they may not be final calls, it will give you a much better idea of what will happen," said FOX 13 political editor Craig Patrick.

And for even better insight, look deeply into the Florida returns.

How did President Trump do in areas with lots of Hispanic voters?

How about Former Vice President Biden in areas with older white voters?

Did either win a certain county by more, or less, than expected?

"When you break down Florida county by county, region by region, it will give you a sense of how other regions and other states are going to vote," said Patrick.

And remember, as the counting stretches on, there could be lead changes in individual states.

More Democrats are expected to have voted by mail, while most Republicans did so in person or on Election Day.

Early returns could favor Democrats, while later ones could favor Republicans.

Leads can change several times as counting different groups of ballots proceeds.