Boston Marathon 2018 Weather Forecast: Impact on Finish Times

By Raymond Britt 

Weather forecast for 2018 Boston Marathon: raw, wet conditions, 40 degree range at start, mid 50 degrees at end, for an average race temperature of low-50s. Some are terrified of the possibility of heavy rain later in the day. Rain or drizzle I expect; a rainstorm, no. Still, you want to know . . .

How does weather impact finish times in Boston? We've run the numbers correlating weather and average finish times between 1999 and 2017, and it's clear when temperatures exceed 55 degrees, finish times rise, too.
  • Averages 1999 to 2017: Temperature 59 Degrees, Finish Time 3:54
  • Impact of High Temperatures 2004 and 2012: 85+ Degrees, Finish Time 4:13 to 4:18
  • Impact of Low Temperatures: Under 50 degrees in 2000, 2002, 2009, 2015 times ranged widely from 3:41 to 3:54

What about a predictable weather forecast? For those Boston entrants hoping (and perhaps praying) to run the marathon in fairly reliable, comfortable race day temperatures and conditions, I'm sorry to report that it's quite possible you'll be disappointed. I've seen it again and again; on race day, things change from hour to hour. Be prepared.

I've been in Boston for the marathon since 1996 (13 consecutive finishes, recent years as a journalist) and my experience is not encouraging, I'm sorry to say, But I'll share because you should be prepared: weather conditions can range from brutal nor'easter forecasts (wicked winds + heavy rain) to oppressive heat, as in 2004.

This chart illustrates race day temperatures from Hopkinton to Boston between 1999 and 2013 show they fluctuate from year to year.

Temperatures will vary during the 3, 4 or 5 hours it takes to cover the 26.2 miles between Hopkinton and Boston. But there’s no comfort in knowing that because the odds of temperatures increasing or decreasing from start to finish are 50/50.

Since 1999, temperatures have risen on the way to Boston in seven years; they declined in seven other years, and remained flat once.

What about just waiting until the race weekend, or even race morning forecast? Surely they will be accurate enough to give the Boston runner confidence in conditions. Nope. The race weekend and race morning forecasts are no guarantee of what you’ll experience on the starting line a few hors later.

I’ve experienced the surprise weather in nearly half of the 13 Boston Marathons I’ve finished. 1999, 2004, and 2007 stand out as races that differed sharply from the forecast.

In 2004, we were told the day might be a little warmer than usual, and many runners were crushed by overheating and dehydration as temperatures soared well above anyone’s guess.

Three years later, we fully expected to be slammed by headwinds from an all-but-guaranteed Nor’easter storm; instead it was a little windy with drizzling rain.

To try to avoid being crushed by conditions, I learned to take enough gear to Hopkinton so I could suit up in running gear that best seemed to match weather, just minutes before the race began. Everything else went into the gear-check bag, to be driven back to Boston for post-race retrieval.

This year, however, with the elimination of a gear check in Hopkinton, runners will have to decide what to wear for the marathon hours before the race begins. That just made things a little more difficult for runners concerned about being prepared for the right temperatures and running conditions.

But no one said anything was easy about the Boston Marathon. Tough, incredibly unpredictable and unstable weather conditions will be one more reason you can have an awesome feeling of achievement when you finish in Boston.

You will have not only qualified, but you’ll have started the best race in the world shoulder to shoulder with the best runners in the world; you’ll have battled your way through any and all obstacles weather changes might throw at you; and when you finally reach the last half mile on Boylston Street, you’ll see the greatest finish line in racing.

Nothing stopped you, especially unpredictable and potentially devastating weather.

Enjoy every moment as you approach the end, allow yourself to celebrate your incredible achievement, cross the line, and become a member of one of the most exclusive clubs in racing: Boston Marathon Finishers.



Boston Marathon Weather Impact 2012: The Heat Year

Featured by USA Today
What's the impact of weather conditions on Boston Marathon Finish Times? We've analyzed weather conditions and finish times by age forecast temperatures soar into the 80-degree range on race day, as they did in 2004 and 2012, we would expect:
  1. Slower Overall Finish Times by 20+ Minutes on Average
  2. Men Tend to Suffer More --  Extreme Heat Reduces Men's Finish Times More than Women at Most Age Levels
  3. More Women Won't Finish -- Up to 20% of Entrants Will DNS (Not Start) or DNF (Start but Not Finish) 
  4. Expect the Unexpected: Boston Conditions Could Defy Forecasters
1. Slower Overall Finish Times by 20+ Minutes on Average
Featured by Runner's World

Our analysis comparing average finish times with race day conditions indicates that temperatures averaging above 60 make a clear difference. Temperatures in the 2012 race exceeded 86 degrees; the brutal heat slowed runners by 28 minutes, on average.

2. Men Will Suffer More --  Extreme Heat Reduces Men's Finish Times More than Women at Most Age Levels

3. More Women Won't Finish -- About 18% of Entrants Will DNS (Not Start) or DNF (Start but Not Finish) 

4. Expect the Unexpected: Boston Conditions Could Defy Forecasters

However, often forecasts can be somewhat unreliable as the weather changes unexpectedly on race day. In 2007, a major storm with significantly high winds was forecast, but conditions eased hours before the race began, to a merely windy and chilly rainfest.

In 2004, a relatively warm day was forecast, but the temps soared beyond expectations. The heat caused much suffering on the course, as the very slow finish times indicate. Then again, in 2005, similar temperatures were forecast, but race day conditions, while warm, did not come close to 2004 levels.

Regardless of the forecast, what you experience at the starting line in Hopkinton can differ radically from what you'll face once past Heartbreak Hill, heading toward Boston. Variability in conditions has been significant in recent years, from one of the hottest races in decades (2004) to the cool, rainy conditions in 2007. See weather conditions for the last 12 years below.

Wondering how weather affects finish times elsewhere?

The 2010 Chicago Marathon was a hot one, temperatures soaring into the 80s. A total 36,159 runners made it through high temperatures to cross the finish line. While the heat did not rival 2007, and the mid-event cancellation of that race, the 2010 race was marked by a much higher than average finish time -- 4:43:38 -- and roughly 2000 runners dropping out. And this result was consistent with an analysis we had conducted before the event.

Before the Chicago race, we wondered: how do differing temperatures impact average finish times? We plotted the average finish times and average race-day temperatures for the last 11 years to find the answer.  And it seemed to be generally good news for runners as long as temperatures stay below 65 degrees. However, when the average temperature soared over 65, average times would drop, we noted.

And that's just what happened in 2010: high 70s average temperature, and a 4:43:38 average finish time.

In earlier years, when the average temperatures are between 40 and 65 degrees, average finish times may vary within a range of between 4:19 to 4:27. Only an 8-minute difference. Not bad. The exception year was 2008, when a 57 degree average temperature was met with a very slow finish time; we'd venture to say this is because runners were being extremely cautious, in the wake of the 2007 meltdown.

What conditions will Boston marathon runners experience on race day? Time will tell, in more ways than one.

[And for everything else, see our Complete Boston Marathon Coverage and our Boston Marathon Stats and Analysis page.]

As Published in USA Today