Beyond The Forecast: Marathon Monday Weather--And Some History

BOSTON (CBS) -- Here we are counting down the few remaining hours until the beginning of the 121st running of the world's oldest marathon. The great Boston Marathon truly signals the official start of spring here in New England, as tens of thousands of people run past a packed Fenway Park on Patriots Day. How sweet it is!

In true New England fashion, the weather isn't always that cooperative. Over the decades, runners here in Boston have had to brave just about every imaginable extreme weather condition from snow squalls to downpours. In the last 10 years alone, we have experienced a veritable potpourri.

In 2007, a nasty coastal storm released 2-4" of rain the night before the race. Strong winds caused some tree damage across the region. Fortunately, the storm accelerated enough so there was only residual drizzle and some showers with brisk conditions for the race. A week before that marathon, there were some early indications that it could turn into a monstrous snowstorm especially farther inland especially out closer to Hopkinton and I mentioned on my WBZ-TV weathercasts that if in the outside shot that solution verified, the race might have to be rescheduled. Race director Dave McGillivray called and stated that I almost gave him a heart attack! Anyway, as the big event got closer, it appeared the storm would hug the coast more tightly enabling the atmosphere to stay sufficiently warm to negate the snow threat. Whew!

Snow has not been a major factor over the years, but there were a few cases such as the snow squalls that accompanied the runners for the first 5 miles back in 1967. Statistically, the chance of rain falling during the race is about 10%. Rain was a factor for many runners in the 2015 marathon as the temperature dropped into the lower 50s to upper 40s. Over the past decade, the 50s have been the dominant temperatures during most of the marathons.

On the flip side, an absolute scorcher struck the 2012 Boston Marathon as temperatures topped out in the range of 85-90 degrees. Chris Troyanos, medical coordinator of the Boston Marathon, frequently consulted with me about the specifics on that impending wretched heat and humidity and his team elected to offer the 26,716 race entrants to defer entry until 2013. As a result, about 4,000 runners heeded the warning about the "red-zone condition."

The 1976 Boston Marathon was the hottest ever, with blistering heat and stifling humidity. It was dubbed the "run for the hoses" marathon for obvious reasons. More than 40% of the runners were not able to finish the race--That year there were only 1,942 starters!

Last year, it started out rather chilly in the 30s to lower 40s, but there was a steady and rapid rise through the 50s into the middle 60s topping out at 67 in Boston during the afternoon.

The city's Easter Sunday high temperature today almost matched that record 87 set during the 2012 Boston Marathon! Fortunately, a cold front will shove this heat offshore tonight but it will be quite mild from the get-go with early morning low temperatures in the upper 50s to lower 60s. However, there should not be a rapid rise in temperature during the race. It will likely rise about 4-6 degrees during the marathon topping out near 70.

The humidity will actually increase a bit tonight as dew points climb into the lower to middle 50s but with the passage of that cold front in the early morning hours, the humidity will drop with dew points slipping quickly back to the middle to lower 40s by race time with even drier air yielding dew points in the 30s by late morning or midday. So, thankfully, we will not experience the dangerous heat of 2012 when over 2,000 runners were treated for heat stroke. Nevertheless, it appears that the heat will still be of concern for doctors and race officials once again this year. Running 26 miles at near 70 degrees can lead to some heat-related problems but the very low humidity will lessen the threat. Nevertheless, those running this year should consult their doctors and be aware of the warning signs and best practices to avoid heat stress complications.

The good news is that the projected west-northwesterly wind of 10 up to 25 mph in gusts will act as an evaporative and cooling agent. It will be primarily a tale wind with some cross components at certain intervals along the race course. The wind will decrease and become more northerly during the afternoon. The sky will feature varying amounts of high and some mid-level cloudiness which will filter and perhaps even blot out the sunshine at times through midday. The visibility will be excellent. The weather will be fantastic for spectators and volunteers but perhaps a bit too warm for some of the runners.

No matter what you have for a race time, completing the Boston Marathon is an amazing accomplishment. GOOD LUCK runners!!!!