Halloween, quite bluntly, is going to be rather nasty. It will be wet, windy, and eventually white by the end of the day.
Rain will continue tonight and throughout the morning hours of Thursday. Winds will increase throughout the day becoming sustained out of the north-northeast between 15 and 25 MPH, gusting up to 35-40 MPH. Because of this temperatures will be unable to warm up, starting off the day near 40, then gradually falling through the 30s during the afternoon. Rain will transition to snow from northwest to southeast late afternoon into the early evening.
Between 6pm and 8pm, the prime time for trick-or-treaters, temperatures will be in the mid-30s, but with the gusty winds it will feel like the low to mid-20s. After sunset (6:32pm) the precipitation type should be primarily snow showers. Overall, it will be an extremely cold and wet evening for the last day of October.
Given the timing of the snow during the evening after dark, minor accumulations are possible. The ground is very warm this early in the season, so that is expected to cut back on totals. In general, I expect 1 inch or less across much of mid-Michigan, although a localized amount near 2 inches is possible, especially across central MI. If you want a chance to see more than 2 inches of snow, you'll need to head northwest of a line from Muskegon to Clare. High temperatures will be back in the low-40s on Friday, so all the snow will melt rather quickly.
Winter Weather Advisory:
The National Weather Service has issued a winter weather advisory from 2PM Thursday until 8AM Friday for the following counties: Clare, Newaygo, Mecosta, Isabella, Muskegon, Montcalm, Ottawa, and Kent. This means snow accumulations of 1-2 inches in these areas, combined with gusty winds, will lead to hazardous travel conditions at times. You should use extra caution while driving and allow extra time to reach your destination.