Rob Macedo, KD1CY, writes on wx1box.org:
.Strong Storm System will bring mild temperatures through Southern New England including along the Boston Marathon route along with the potential for rain and heavier downpours and potentially isolated thunderstorms with attendant lightning risk. There is also the potential for strong winds during Marathon Monday under any heavier rain showers and thunderstorms and then as a cold front pass through the area late Monday Afternoon as the marathon ends, through Monday Night and into early Tuesday Morning..
..Boston Marathon volunteers and runners should prepare for the rain and changeable temperatures with largely mild conditions but a slightly cool start and a cooler mid to late afternoon from west to east across the marathon route..