A little wave of low pressure will zip into the region early Saturday morning. For the race’s start time at 7:30 a.m., rain may not have yet begun, but by around 9 a.m., rain is likely. The rain shouldn’t be particularly heavy, but may well fall steadily between 8:30 a.m. and 1 p.m. or so. Amounts will probably be around 0.1-0.2 inches.
It will be a chilly rain too, with temperatures in the low 40s to begin and only rising into the mid-40s by the race’s conclusion early afternoon.
Winds out of the north and northeast at around 5-10 mph shouldn’t be a major factor.
Here’s a graph showing predicted temperartures, rain, and wind from the National Weather Service during the day Saturday.
For marathon newbies, here are a couple good resources that provide tips for running in rain and cold rain:
Runner’s World: Marathon in the rain tips
New York Daily News: Expert tips for running in the rain