How you know you're close to the election: Weather.com has forecasts ready:
Denver, CO Sunny, 60F
Las Vegas, NV Sunny, 75F
Albuquerque, NM Sunny, 65F
Billings, MT Scattered Showers, 49F
Kansas City, MO Sunny, 64F
St. Louis, MO Scattered Showers, 67F
Minneapolis, MN Showers, 54F
Milwaukee, WI Scattered Showers, 57F
Indianapolis, IN Scattered Showers, 65F
Cleveland, OH Scattered Showers, 60F
Cincinnati, OH Scattered Showers, 65F
Pittsburgh, PA Scattered Showers, 58F
Philadelphia, PA Showers, 58F
Manchester, NH Scattered Showers, 54F
Arlington, VA Scattered Showers, 62F
Roanoke, VA Rain/Snow Showers, 49F
Charlotte, NC Scattered Showers, 61F
Atlanta, GA Mostly Sunny, 65F
Jacksonville, FL Mostly Sunny, 74F
Miami, FL Scattered T-Storms, 80F
Temperatures look to be above-average in most swing states, although there's a chance of rain most everywhere but the Mountain West. Too early to say if anything truly nasty will develop.
Conventional wisdom (and at least one econometric study) holds that poor weather does indeed help the Republicans. But might the reverse be true in a year when Democratic enthusiasm significantly outpaces Republican enthusiasm?
Two implications worth considering. Firstly, the most important factor might be the weather patterns within a given state. For example, if it's rainy and dismal in Democratic-leaning Cleveland, but relatively dry in Southern Ohio, that probably helps the Republicans. If it's nice in NoVa but there's freezing rain in the Virginia panhandle, that probably helps the Democrats.
Secondly, a candidate would prefer depressed turnout in a state where he has a substantial advantage in early voting. The states where Democrats have the most significant advantages in early voting seem to be Nevada and North Carolina ... they might want to root for poor weather there.