Perceived Temperature For Runners Version 1
This chart gives an idea of what the perceived temperature is while running. This chart has been replaced by a more sophisticated approach at Perceived Temperature For Runners Version 2.
Normal heat indexes assume a person walking outdoors at 3 mph and generating 180 watts per square meter of skin. The original work states "higher levels of activity would increase the sensitivity to humidity… few people, however, sustain activity above the level considered here for long enough to reach a steady state". This is not very helpful to runners that are moving far quicker than 3 mph and generating a lot more heat. Ideally, I'd go back to the original perceived temperature work, recreate the mathematical models and plug in different values for the heat generation for runners. Sadly, I've not found an easy way of doing that. Instead, I have taken a simple approach based on the idea that in cold weather, the perceived temperature is about 20f warmer than the actual temperature. The chart below is based on the standard perceived temperature calculation, but with 10f added to the actual temperature. The chart below is a first pass at what running at a given temperature and humidity would feel like to someone walking. So running at 76f and 80% humidity would feel like walking in 100f temperatures.
2 Impact of Humidity
The graph below shows how core temperature (of walkers) on the Y-axis rises with humidity on the X-axis for different air temperatures (lines). You'll notice that at 24f/75f there is no impact of humidity on core temperature. For temperatures between 33c/92f and 45c/113f, the humidity does not change core temperature until a critical point is reached and then there is a dramatic rise. By 50c/122f, even changes in very low humidity make a big impact on core temperature. It seems reasonable that a similar response would be seen in runners, but at lower temperatures.
3 Dew Point
Runners World suggested that dew point could be used in isolation, and published the simple table shown below. This seems an overly simplistic and flawed approach. For instance, at 3:51 pm 23 Jul, Phoenix, AZ was 105f with a dew point of 55f, which the table below would say is at the low end of "Comfortable, Hard efforts likely not affected". I believe that 105f, even with low humidity would not be comfortable and it would impact my performance.
|DEW POINT (°F)||RUNNER\'S PERCEPTION||HOW TO HANDLE|
|50–54||Very comfortable||PR conditions|
|55–59||Comfortable||Hard efforts likely not affected|
|60–64||Uncomfortable for some people||Expect race times to be slower than in optimal conditions|
|65–69||Uncomfortable for most people||Easy training runs might feel OK but difficult to race well or do hard efforts|
|70–74||Very humid and uncomfortable||Expect pace to suffer greatly|
|75 or greater||Extremely oppressive||Skip it or dramatically alter goal|
4 Other Sports
This page is focused on runners, but may apply to some other sports such as soccer. It would not apply to cycling or similar sports where there is more air movement.