Voters are casting ballots today in a special election to fill a Senate seat left vacant by Virginia Attorney General Mark Herring, left. (Steve Helber/AP)

Control of the Virginia state Senate may be determined by which party’s loyalists have the best snow tires. Voters will have to contend with up to half a foot of snow as they head to the polls to fill a seat left vacant by new Attorney General Mark Herring (D).

The district, based in suburban Loudoun and Fairfax Counties, leans Democratic. President Obama won 59.3 percent of the vote there in 2012, but Herring won reelection in 2011 with just 54 percent of the vote; turnout in a special election, especially with such bad weather, is expected to be much lower, giving Republicans a chance at the upset.

Democrats need to keep Herring’s seat, and a seat formerly held by Lt. Gov. Ralph Northam (D), to maintain a 20-20 tie in the state Senate. Northam would cast tie-breaking votes if the chamber remains evenly split; Republicans have requested a recount in the race for Northam’s seat, where Democrat Lynwood Lewis won just nine more votes than Republican Wayne Coleman  out of more than 20,000 cast.

But Republicans face another hurdle: a soon-to-be former Republican delegate, who was upset in last year’s primary, running as an independent. Our colleague Ben Pershing explains:

In a race that could determine control of the Virginia Senate, in a bellwether county of a purple state, in a party that is split ideologically, Joe T. May is the man in the middle.

Between a Republican lauded by the party’s right flank and a Democrat backed by her side’s leadership, May is trying to shoot the gap[.]

May is running as an independent, just days after his service as a longtime Republican member of the House of Delegates came to an unexpected end. As he tries to lure support from Democrat Jennifer Wexton and Republican John Whitbeck, May hopes to persuade voters to ignore party labels and choose him — a grandfatherly engineer and veteran legislator who lost his House seat last year in a primary against a more conservative Republican.

“There are three of us in this race,” May explained to a roomful of AOL employees Thursday, “and we have somebody who’s relatively far right and somebody who’s relatively far left and quite frankly, they’re pretty much paralyzed by partisan politics. One of the nice things about being an independent is that you have a great deal more latitude in doing what you think is the right thing.”

May visited AOL’s office in Sterling as part of a tour of businesses in the 33rd District, which is split roughly 70-30 between Loudoun and Fairfax counties. Before he spoke, May was introduced as “somebody who transcends politics.”

The 76-year-old May said he’s always been a Republican and expects to caucus with the GOP if he wins — which would give the party control of the Senate. “But I’ve also been pretty darn independent,” May said.

The three candidates’ differing strategies are clear in their ads — Wexton and Whitbeck hope to fire up their respective bases, and May is aiming for the middle.

Wexton, a former Loudoun prosecutor, has sparked controversy with an ad featuring her in a courtroom discussing her fights on behalf of rape victims. “In the Virginia Senate, I’ll fight just as hard against tea party Republicans who would take away a woman’s health care and her right to choose, even in cases of rape and incest,” she says.

Whitbeck, a lawyer who heads the 10th Congressional District Republican Committee, has aired an ad saying there’s “not a dime’s worth of difference” between May and Wexton, calling both “liberal politicians with risky agendas” who support higher taxes.

May’s tone is a bit lighter.

“Legends of the game! Joe Namath. Joe Gibbs. Joe May?” asks the narrator of a May ad — before noting his role in designing the first-down line.

“That’s cool, but kinda nerdy,” says a woman pictured on-screen. The ad concludes with the narrator urging, “On Jan. 21, vote for the nerd.”

Polls are open from 6 a.m. to 7 p.m.