Your amateur meteorologist has summarized the "tracking polls" for tomorrow's Manchester, New Hampshire, weather forecast. Snow is possible. Read on for details.
Taking Manchester, New Hampshire, as the forecast center for the state,
Weather.com (which bases its forecasts primarily on the National Weather Service) predicts that snow will start at around 9 a.m. on Tuesday, increase in intensity starting around noontime, and continue past the close of the polls. However, even if the snow doesn't start until mid-morning, the forecast is for bitterly cold temperatures, in the low to mid single digits, and that might keep some old folk away. Those numbers should still be higher than Al Sharpton's vote percentage, however.
Accuweather predicts only a "chance of snow" with a couple more degrees of temperature (but still pretty cold, especially in the morning).
The National Weather Service predicts snow to start Tuesday night, "especially after midnight." They also predict slightly warmer (but still cold) temperatures than Weather.com.
The aviation weather products that cover some of Tuesday's weather have been released, but they make no mention of snow yet. (Not surprisingly they're consistent with the National Weather Service's general forecast, since they come from the same source.) I believe the next set of aviation forecasts comes out at 7:00 p.m. Eastern tonight, and they'll be much more precise.
Weather effects are a bit unpredictable for this race. However, in a close race, it could make a difference.
Candidates may need to be very careful about arranging their safe departures from New Hampshire to continue on to February 3rd states for appearances on Wednesday morning. However, I'm expecting them to have no significant problems unless there's a true blizzard, something not expected at this point. As long as Manchester can keep its airport runways relatively clear, and as long as the snow doesn't reduce visibility too much, all the candidates should be able to escape. However, South Carolina could still have some problems with ice. (Trying to land on an ice sheet is never a good idea. I did it once when there was some sand spread over the ice, with a really long runway, but it wasn't fun.) I didn't check the runway conditions in Charleston, so I don't know what they're like at the moment, but southern ice storms can keep some airports effectively out of commission for days if bad enough.
Conventional wisdom suggests that bad weather disproportionately keeps more seniors from getting to the polls, and it also drives down turnout among less committed voters. Ultra-urban areas are perhaps less affected by bad weather (since you can vote in your own building), but New Hampshire has very few such polling places.