Feeling the Heat: How Temperature and Course Conditions Affect Western States 100 Finishing Times

An analysis of the effects of heat and course conditions on finish times at the Western States 100.

By on June 22, 2023 | Comments

I love when quantitative data helps us spot patterns and gain insights that we may have otherwise overlooked. Sometimes, though, the numbers simply help us articulate a phenomenon we already knew existed. That’s certainly true when it comes to talking about the impact warm temperatures play on runners’ performances at the infamously hot Western States 100, which takes place annually in California in the summer.

There is an existing body of research confirming warmer temperatures are linked to slower finishing times in endurance running. Many of these studies focus on the marathon distance, such as these from 2019, 2012, and 2012). Ultrarunners are also affected by the heat, of course, which is why we incorporate heat acclimation into our race preparation, adopt strategies for coping with the mental strain of racing in the heat, and utilize cooling strategies to mitigate its physiological effects.

When Joe Uhan described the Western States 100 as a “killing machine” that chews up and spits out ultrarunners, he identified the heat as a significant contributor to that carnage.

This month’s edition of “Running the Numbers” is here to tell you the same thing, but with some charts. We also look briefly into how course conditions — namely residual snow in the race’s higher elevations — affect runners’ finishing times.

We’re publishing this article just ahead of the 2023 edition of the race, where temperatures are forecasted to be well below normal for the region. It’s still going to be warm though, and that warmth will play into the race dynamics. The region saw historically high snowfall in the winter of 2022-2023, and not all of that snow has melted, so runners will experience the effects of this, too.

In this article, we uncover some great nuance by digging into the data, so read on for insights on how temperature and course conditions impact runners by finishing hour, age group, and gender.

Beth Pascall - 2021 Western States 100 - Robinson Flat

Beth Pascall leading the women at Robinson Flat (mile 30) on a hot day at the 2021 Western States 100. Photo: iRunFar/Bryon Powell


The Western States 100 is one of my favorite races to analyze because it has a strong culture of data: All of the data for this article comes from the Western States website and its results on UltraSignup. For this article, I only considered race results from 1985 onward because, according to the Western States website, previous editions of the race were shorter than its current distance of 100.2 miles. I also didn’t want finisher rates from the earliest years of the race to skew the results since, for example, the first four editions had a combined 17 runners start the races with only five finishers.

To compare race results across years, I took a subset of race results from the hottest and coolest editions of Western States, based on the warmest temperature reached on race day (the daytime high). I coded any year where the daytime high was 85 degrees Fahrenheit (29 Celsius) or cooler as a “cool” year, and years where the daytime high was 95F (35C) or warmer as “hot” years. This on its own emphasizes how much heat plays a factor in performances at Western States, because I probably wouldn’t consider 85F to be cool in many other contexts. Using this coding system, nine years were classified as “cool” years — the most recent being 2019 — and 12 were considered “hot” — including the 2022 and 2021 editions.

2019 Western States 100 - Jim Walmsley

Jim Walmsley on his way to resetting his own course record at the 2019 Western States 100. With a high of 83 degrees Fahrenheit, 2019 falls under the heading of “cool” for this analysis. Photo: iRunFar/Bryon Powell

Finish Rates Aren’t Strongly Linked to Temperature

First, the good news for Western States entrants: There is not a strong correlation between higher temperatures and lower finish rates. While the data does indicate the heat slows you down, it is not necessarily a DNF sentence. The actual risk of getting a DNF on a particularly hot day at Western States may depend on an individual runner, their pacing strategy, and how close they would be to cutoffs on a cool day.

The chart below shows each edition of the race, from 1985 onward, as a data point. We did not include a trend line because a linear trend line would have a low R2 value, or coefficient of determination. That figure, between 1 and −1, is intended to measure how reliably you can predict, in our case, the finish rate based on the temperature. In other words, we can’t confidently say there’s a strong correlation between hotter temperatures and lower finish rates.

Feeling the Heat at Western States 100 - graph 1 - v2

Scatter plot showing the correlation between daytime high temperature and finisher rate at the Western States 100.

Western States publishes finish rates for each edition of the race on its website, but data on which runners did not finish (DNF) is not available on UltraSignup for all years. Therefore, I did not drill down into whether factors such as age group or competition level impacted a runner’s likelihood of getting a DNF.

How the Distribution of Finishing Times Changes with Different Temperatures

Proportionally speaking, the most pronounced effects of the heat are seen at the very front and back of the pack. There are relatively more runners finishing in 19 hours or less on cool years when the daytime high was 85F or cooler. There are 3% more runners finishing in what is called the Golden Hour of the race on hot years, pushing hard for finishes of 29 hours or longer but within the event’s 30-hour cutoff.

Bar chart

Bar chart showing the distribution of finishing times on hot and cool years at the Western States 100.

This general trend of finishing times being slower on hot years is true of both men and women. On particularly hot years, both the men’s and women’s fields have proportionally more runners finishing in the final hours of the race.

One interesting trend highlighted in the charts below is that there are proportionately more runners in the men’s field finishing between 23 and 24 hours. Western States awards a silver buckle to every runner finishing in 24 hours or less, and it appears that incentive has a more visible impact on men’s finishing times.

Bar chart

Bar chart showing the distribution of male finishers by the hour on hot and cool years at the Western States 100.

Bar chart

Bar chart showing the distribution of female finishers by the hour on hot and cool years at the Western States 100.

With respect to age group, the heat appears to have a less pronounced impact on the finishing times of finishers aged 40 and under. When comparing results in cool and hot years by finishing hour, the proportion of these runners finishing within a particular hour never varied by more than 1%.

The effects of heat were a little more pronounced among runners aged 40 and over. Finishers in these age groups were relatively closer to the 30-hour cutoff in the hottest years. Notable findings for these runners included:

  • Meghan Canfield is the only grand master (runners aged 50 and over) to finish in under 20 hours on a hot year; finishing in a time of 19:30:50 at the age of 52 in 2013, when the temperature peaked at 102F on race day.
  • On hot years, 37% of all finishers aged 50 or over have a finishing time of 29 hours or more, compared to 32% of grand masters finishers in cool years.
  • The proportion of masters runners (aged 40 to 49) finishing in the Golden Hour jumps from 16% to 23% when comparing results from the races coolest and hottest years.

Course Conditions Also Affect Finishing Times

Continuing with our findings you already knew but can now quantify, the Western States course is faster when there’s no snow on it.

The Western States course starts in Olympic Valley, California, with runners climbing an escarpment and then spending some miles in the high country before descending into the canyons and eventually the low elevation finish line. Runners are ferried across the American River by boat, located at mile 78 on the race course, on years when water levels are high, and cross on foot with the assistance of a guide rope when water levels are lower. Western States publishes historical data for years when snowpack was notable and therefore water levels were likely high and boats were more likely used at the river crossing.

For years when Western States has noted moderate snowpack or a snow route in its results archive, the median finishing times are over 20 minutes slower compared to years where snow conditions were not noteworthy.


Table showing finishing times on years with snowpack conditions and boat-assisted river crossings at the Western States 100.

2022 Western States 100 - Adam Peterman - Rucky Chucky

Adam Peterman makes his way across the Rucky Chucky river crossing at mile 78 of the 2022 Western States 100. Photo: iRunFar/Bryon Powell

Closing Thoughts

Looking to the future, it will be fascinating to see whether the temperature factor will be different for runners at Western States. On one hand, more runners are adopting science-based cooling protocols to mitigate the physiological and psychological effects of warm temperatures. On the other hand, climate scientists warn we can expect warmer temperatures and extreme weather such as forest fires to continue affecting us. I am deeply invested in that future, but cannot comment on it. I have a spreadsheet, not a crystal ball.

Call for Comments

  • Did you expect the impact of heat on finishing times and finisher rates to be more or less pronounced?
  • Does your own experience of running in heat align with these findings?
  • Any last-minute advice for Western States 100 runners preparing to contend with the course and possible heat?
Mallory Richard

Mallory Richard is a data analyst and trail runner in Winnipeg, Canada.