It's only May, but in Alaska, September feels like it's just around the corner.

Sen. Mark Begich (D) of Alaska at Washington Post Live's Energy & the Election breakfast forum at the Democratic National Convention in Charlotte, North Carolina. (The Washington Post)

That's because Republican and Democratic groups and candidates have been rushing to reserve TV air time for commercials in the fall to influence the outcome of the U.S. Senate race, one of the most important showdowns in the battle for control of the Senate. No other top-tier Senate contest has seen such a flurry of groundwork. Then again, no other top-tier Senate race is being held in a state where advertising is so cheap.

The National Republican Senatorial Committee became the latest group to reserve time in the fall, shelling out $2.2 million for a period between Labor Day and Election Day -- the most important part of the election cycle, when voters begin seriously looking at the campaign and candidates.

As Reid Wilson reported on GovBeat earlier this week, Sen. Mark Begich (D) and two groups backing his campaign have purchased a combined $6.4 million in television time for the fall.

The NRSC fall reserve comes as GOP frontrunner and former state attorney general Dan Sullivan and a well-heeled group backing him have also reserved lots of fall air time.

As Reid reported in the Read In, Sullivan has reserved about $480,000 in air time from late-September through the election. American Crossroads, a Republican super PAC supporting Sullivan, has reserved $700,000 worth of cable advertising in September.

Okay, that's a lot. But it's not nearly as much as advertising would cost in more populous state like North Carolina and Georgia, which are also hosting battleground Senate contests. And that's why both sides are lining up early in Alaska.

Only three states have smaller populations than Alaska. That means the cost of gross ratings points, which measure the percentage of an audience likely to see a given ad one time,  is substantially cheaper there than it is in other states. North Carolina and Georgia, by comparison, are both in the top 10 most populous states.

As the battleground races come into sharper focus as the year goes on, groups will have to make decisions about where to spend (and where not to) down the stretch. But given the low cost of advertising in Alaska, it's a no-brainer to be on the air there unless the race drastically swings toward one side or the other, which seems unlikely.

The contest is shaping up as a close one. The Republican primary isn't settled yet, but Republicans have begun to coalesce around Sullivan, believing him to have a strong chance against Begich.

Another reason groups are shelling out money for the fall: Reserving early means paying lower rates. This is true everywhere, not just in Alaska.

The ad reservations, it should be noted, are subject to change.

The key takeaway is that overall spending will probably be pretty close to even when all is said in done in Alaska. That's probably good news for Begich. Whereas in North Carolina, Sen. Kay Hagan (D) has been barraged by the well-heeled Koch brothers-backed group Americans for Prosperity and may continue to be outspent on the whole, Democrats can afford to hang with AFP and other conservative groups in Alaska.

That's why the Last Frontier is actually first on the minds of many Republican and Democratic strategists this year.