The answer to "How bad can Boston weather be on Marathon Day?" is . . . very, very bad.
Ideal Boston Marathon weather means a temperature of around 45-50 degrees, overcast skies, enough moisture in the air to make breathing comfortable and minimize dehydration - and a southwest breeze to act as a tailwind.
Sometimes Boston Marathon weather really does hit this ideal mark.
But not very often.
After all, April weather in Boston usually includes plenty of cool damp gray days, and average April temperatures hit the ideal comfort range more often than not.
But...this is a good example of why "average" can be misleading.
For example, let's look at 2012. Weather forecasters predicted the worst type of weather for a marathon runner: sizzling hot, with temperatures zooming up to 90 degrees and sunny, cloudless skies.
Unfortunately for the runners, they were right . . . even though the thermometer topped out at only 87°.
How often does Boston weather on Marathon Day soar to almost ninety - or above?
More frequently than you might expect.
We get questions periodically about the weather, such as this one from Tim. We did some research using historic weather data, and we were shocked by what we found. You may be too.
Is there a record of the high temperatures for each Boston Marathon?
I'm planning to run in the Marathon - so I'd like to see what the high temperature was on each day the Boston Marathon has been run. That way, maybe I'll know what to expect?
We dug deep into Boston Marathon weather history to find temperature highs to answer Tim's question, expecting not to find any days hotter than around 70 degrees. After all, April is still usually a cool month, right?
To our surprise, we discovered that while the 87° high temperature for 2012 may be atypical, it wasn't unusual and it didn't even set a Marathon Day temperature record.
Take a look at these Marathon Day high temperatures for Boston - and prepare yourself for a few surprises:
1905 - 100 degrees
1907 - Occasional snow
1908 - Snowflakes, drizzle
1909 - 97 degrees
1925 - Cold wind, snowflakes
1927 - 84 degrees
1952 - 84 degrees
1961 - 39 degrees; snow squalls
1967 - Snow squalls
1961 - 39 degrees; snow squalls
1967 - Snow squalls
1970 - 38 degrees; driving rain, sleet
1976 - 96 degrees
1982 - 68 degrees
1987 - 87 degrees; 96% humidity
1999 - 68 degrees
2000 - 47 degrees
2001 - 54 degrees
2002 - 56 degrees; heavy mist
2003 - 59 degrees
2004 - 86 degrees
2005 - 66 degrees
2006 - 53 degrees
2007 - 50 degrees; strong wind, torrential rain
2008 - 53 degrees; heavy mist
2009 - 47 degrees
2010 - 49 degrees
2011 - 55 degrees
2012 - 87 degrees
2013 - 54 degrees
2014 - 63 degrees
2015 - 44 degrees; driving rain, wind
2016 - 61 degrees
2017 - 73 degrees
2018 - 43 degrees; drenching rain, strong wind
2019 - 63 degrees; light to heavy showers, thunderstorms
No, the 1905 high temperature for Boston is NOT a mistake - it really did soar to 100 degrees, according to the Boston Globe.
And the temperature reached almost that high (97 degrees) just four years later in 1909 and then again when it hit 96 degrees almost 70 years later in 1976.
Keep in mind that because the Boston Marathon is held on the third Monday of the month, it falls on slightly different dates each year, ranging from April 15 through April 21.
So the temperatures that you see above are not necessarily the highest temperature ever recorded for that particular date - they're just the highest for that date when it also happened to be Marathon Monday.
How to Train for the Boston Marathon's Unpredictable Weather
Given Boston's unpredictable weather and the wide range of high temperatures on Marathon Day, you're best bet is to train for extremes so that you'll be prepared for whatever you encounter.
In addition to training in hot and cold weather, try also to train in heavy rain, sleet, snow, strong wind, and high humidity.
Don't forget about the Boston Marathon race course's hilly terrain, especially the hills you'll encounter late in the race.
All of these conditions add up to the reason why the Boston Marathon can be challenging!
Can You Expect Any Weather Accommodations for the Boston Marathon?
In recent years, weather accommodations have been made in a few cases:
In 2007, the start time for the Elite Men's race (where the fastest runners compete) moved to 10am from noon.
After a volcano erupted in Iceland in late March and again on April 14, 2010, European flights were disrupted and Marathon entrants who could not reach Boston were allowed to defer their entry until the following year.
When extremely hot weather appears likely, as in 2004 and 2012, the usual number of medical tents will be increased. Typically, about 2-4% of the racers seek non-injury medical attention, but in 2004, with a temperature high of 87°, the total rose to almost 10%, mostly for heat-related reasons.
Due to the 2012 heat predictions, the BAA (the Marathon's sponsor) offered deferrals to the following year to anyone who chose not to run due to the heat. Runners had to elect the deferment BEFORE the race began . . . no opting for the deferral midway through!
Where to Stay for the Marathon: Hotels Overlooking the Route