To modify an expression used to describe the weather in Ireland, if you don’t like the results of the latest Washington Senate poll, wait five minutes and it’ll change. One day incumbent Patty Murray is up by double-digits. The next, her challenger Dino Rossi is the one with the insurmountable lead. So why are the state’s voters so hard to predict? Polling guru Nate Silver thinks he has an answer. Three, in fact.From The New York Times:First, Washington, a technologically-savvy state, has a somewhat higher than usual number of cellphone-only adults, which pollsters may not be capturing. It also has a fair number of Asian-American voters, who can sometimes be hard to reach because of language or cultural barriers.And that third reason? That would be because we’re one of only two states where voting takes place almost entirely by mail.This can wreak havoc with traditional likely voter models, which oftentimes ask questions like “Have you voted in the election precinct before?” and “Do you know where people in neighborhood go to vote?” — questions that are nonsensical in the context of an election that takes place by post. Also — probably because of mail balloting — turnout in Washington and another vote-by-mail state, Oregon, has generally been very high, so targets that might work well in other states could fail there. Finally, since many voters in Washington return their ballots in well in advance of Election Day, a pollster surveying the race close to Election Day will encounter another type of voter — those who claim to have voted already — which traditional likely voter models are not well-designed to handle.Nice work, Silver. But now that you’ve diagnosed the problems, would you care to lay a little skin on the line and take a guess as to who might win?That would point toward Ms. Murray indeed holding a small lead, one that could be somewhat more meaningful than usual given that many ballots in Washington are sent in before Election Day proper and it is hard to make up ground late — although Mr. Rossi obviously retains decent chances.Pffft. Some guru.