The good news, however, is the weather is expected to improve as the day goes on after driving rain, wind and even some thunderstorms dumped on the region early Monday morning.
Those changes are aimed at keeping runners and the race's army of volunteers warm and dry. At one point, the forecast called for morning temperatures in the 30s, with the potential for wind chills in the low 30s, but that has changed significantly. Tent walls and heat will be added at the staging areas, and more ponchos will be available.
In order to minimize the amount of time runners are waiting in the rain, the Boston Athletic Association adjusted start times to condense the amount of time between the third and fourth wave of runners.
Last year's edition of the race was run in cold and windy conditions that made it hard for Kenyan athletes to perform well in the full marathon.
Boston may be in for heavy rain and possibly a thunderstorm, according to the National Weather Service, and wind gusts could reach 28 miles per hour.
"The marathon is run on Patriots' Day or it's not run", BAA CEO Tom Grilk said Friday, according to 4WBZ.