By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer

BOSTON (CBS) – One day closer to the big race and the weather is coming into sharper focus. The main headline has not changed. It still looks wet. I think it is pretty near a lock – there will be some rain around for a good portion of the day on Monday. However, there are some reasons for optimism.

The latest trends show the heaviest of the rain may come very early in the day, largely predawn (say, 1-7 a.m.). The rain wouldn’t shut off after that, but it may become a bit more scattered and light. In fact, by midday and afternoon, there may be large areas where there is no rain falling at all and a few breaks in the clouds. Certainly, it appears as though the later your start time is, the less wet you may get.

(WBZ-TV Graphic)

Then there are the temperatures. Looks like a frontal boundary will likely stay to our south for most of the morning. This would mean onshore winds and temperatures largely in the 40s. One of the biggest remaining questions in this forecast: How far north will the front (and milder air) push? It MAY push though Boston and the race route in the afternoon. If that were to happen, temperatures would spike at least into the 50s, perhaps 60s. These wavy, meandering fronts are very tough calls, certainly not something we can forecast with confidence several days in advance.

(WBZ-TV Graphic)

Finally, the winds – always a vital part of the forecast to runners. The course, in general, goes from southwest to northeast (meaning runners are running east-northeast, for the most part). A west-southwest tailwind is ideal. That is not going to happen. Winds in the morning will be a full-on headwind out of the east-northeast. That being said, wind speeds won’t be nearly as dramatic as last year, generally sustained between 5-15 mph, gusting 20-30 mph. Assuming the front pushes through during the latter portions of the race, winds would shift to a more southerly direction, a crosswind for runners.

(WBZ-TV Graphic)

Lastly, there is a small threat of a scattered thunderstorm on Monday. At this point, the chances are low of this occurring, but it’s worthy of a mention. It’s tough to say how race officials would react to such an occurrence; it is a rarity in mid-April. At this point, just something to keep in the back of your minds if you are running or spectating on Monday.

(WBZ-TV Graphic)

Race Day Forecast

Monday morning: Temperatures in the 40s along the route with a light east-northeast wind (5-15 mph and gusting to 20 mph.) Overcast sky with scattered showers of varying intensity.

(WBZ-TV Graphic)

Monday midday: Temperatures start to creep up with the approaching front. Some 50s now along the route. Shifting winds (with that front) from east-northeast to south (sustained 10-20 mph, gusts 20-30 mph). Again, scattered rain showers.

Monday afternoon: Assuming that front does push through, temperatures are solidly in the 50s, perhaps a few 60s. Winds 10-20 mph out of the south and gusts of 20-30 mph. Few breaks in the clouds possible along with widely scattered showers.

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