DETROIT (AP) — A limited, potentially frustrating Democratic ballot combined with a fresh blanket of snow appeared to be holding down Michigan voter turnout in Tuesday's presidential primary.

Election officials estimated roughly 20 percent of Michigan's 7.14 million registered voters might participate in either the Democratic or Republican primaries by the time polls closed at 8 p.m. But the lack of an active Democratic contest appeared to be driving turnout below that in some communities.

Republicans had a full ballot but Democratic primary voters had fewer choices, since Hillary Rodham Clinton was the only major candidate on the list. Barack Obama and John Edwards pulled their names from the Democratic ballot after Michigan broke national party rules by moving up its primary date. Some of their supporters were urging voters to vote for uncommitted, which could leave some delegates free to back Obama or Edwards. Write-in votes weren't being counted.

"Some people don't understand why their candidate isn't there," said Lansing Clerk Chris Swope, who estimated voter turnout in Michigan's largely Democratic capital city might be about 15 percent unless there was a late rush.

Some voters, who had written in Obama or Edwards on their absentee ballots, were frustrated their votes wouldn't count if they called to fix their error after votes already had started being tabulated.

"I'm only voting the Republican ballot because the Democrats didn't give me any choice," said Lansing's Betsy Reum, 59, a self-described independent who voted for Arizona Sen. John McCain. "I might have voted Democratic had I had a choice."

Oakland County Clerk Ruth Johnson said voter turnout might dip below 20 percent in the politically mixed region in southeast Michigan, unless there's a late rush.

The Republican ballot was expected to attract the most voters because it has a full slate of candidates. McCain and Michigan native Mitt Romney were in a close race, while former Arkansas Gov. Mike Huckabee also was expected to do well.

Snow fell across much of the state Tuesday morning, leaving up to six inches or more in areas including Bloomingdale, east of South Haven, and Burton near Flint, according to the National Weather Service.

But not all areas got new snow. Chippewa County Clerk Diane Cork said Tuesday morning voter turnout appeared slow in her Upper Peninsula county, but she couldn't blame the weather.

The primary date itself is unusual for Michigan, which typically doesn't hold presidential primaries until later in the election cycle. The date was moved up to try and give the state more say in the selection of presidential candidates, but the move at least temporarily cost Michigan all of its Democratic national convention delegates and half its Republican ones.

Party leaders are confident the delegates eventually will be seated.

Precinct returns were expected to come in normally for the most part. Some smaller Michigan counties were going to have to hand count some uncommitted votes, but secretary of state officials did not expect big delays in results.

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Associated Press writers David N. Goodman and Jeff Karoub in Detroit contributed to this report.