637,581 people voted early in Minnesota. Here's what we watched.

Across a six-week stretch of early voting, the number of ballots cast in Minnesota nearly matched the early general election turnout in 2016, according to the Minnesota Secretary of State's data — an initial sign of potentially strong midterm turnout in November.

In 2016, more than 670,000 absentee ballots were received prior to Election Day. This year, more than 600,000 early votes were cast, which roughly matched 2016 and is significantly more than the number who voted early in the 2014 midterms, when early voting was first allowed.

The Star Tribune tracked the early vote here every week until Election Day, with new counts having typically arrived on Thursdays. Here's what we watched as the vote came in:

How does turnout compare to 2014 and 2016?

High early voting numbers could be a reflection of enthusiasm among voters of both parties. It could also suggest that Minnesotans are getting used to recent voting laws, enacted in 2013 and first available in 2014, which allow residents to vote early without an excuse about six weeks before the election.

This election year, 637,581 Minnesotans cast ballots — more than twice the number that had voted early in 2014 and about 40,000 votes behind 2016's tally.

Roughly matching 2016's pace is especially significant because midterm turnout is usually much lower in Minnesota than during presidential years.

Minnesota often leads the nation in voter turnout, and the U.S. Elections Project shows it's one of many states to surpass the last midterm's early vote total.

Are younger voters turning out?

Election forecasters are watching this year's youth vote closely since a significant increase in turnout among those aged 18-to-34 could strongly impact November's results.

This year's early youth vote comprises 12 percent of early ballots filed so far, roughly on par with their 2016 advanced turnout.

Note: About 3 percent of ballots were unassociated with a birth year and therefore not shown.

However, younger early voters also have the highest percentage among age brackets who didn't cast a Minnesota ballot in 2016. This surge of new early voters dovetails with sharp increases in newly-registered youth.

This may also signal many who weren't old enough to vote in 2016 are now engaging with the voting process.

Voters aged 65 or older had the highest early turnout last election and have turned out in similar percentages this year as those voting absentee and via mail often skew older.

Where are the early votes coming from?

Apart from being the state's major population centers, metro area counties like Hennepin and Ramsey often vote heavily Democratic in statewide elections. High turnout there could reflect Democratic enthusiasm, whereas high turnout in outstate counties could mean the same for Republicans.

So far, measuring the percentage of absentee ballots cast by Minnesota county — shaded from less to more — reveals the most early turnout in Hennepin, Ramsey and Dakota counties.

As a percentage of registered voters, counties in northern parts of the state and the Iron Range had among the highest percentages of early voter turnout in 2016. Mail and absentee ballots often comprise a significant percentage of the total vote in greater Minnesota.

What's happening in the suburbs?

The Twin Cities suburbs are home to two heavily contested Congressional races, which could play a role in driving up turnout. The suburbs are also a key battleground in statewide races, so voter enthusiasm there is important to both parties.

So far, more 2018 early votes are on pace to come from Hennepin and Ramsey counties than other areas, just as in 2016.

The other five metro counties — Anoka, Carver, Dakota, Scott and Washington — alone account for about a quarter of the early vote, indicating a significant number of suburban early ballots.

About 39 percent of the early vote has come from greater Minnesota, mostly from the central and southern regions.