storm over town

Heat Index: Deadlier Than Lightning

When we think of weather-related dangers during the summer months, our minds tend to wander towards the catastrophic. Things like tornadoes, floods, fires, or hurricanes. Even lightning is frightening. But are these huge events really the things we should be worried about, day in and day out? On average, heat index kills and hospitalizes more people than all of these other things combined.


Heat Index

Heat index is a basic calculation using temperature and relative humidity and is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. The National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) has put together this easy to use chart to explain the relationship.


NOAA heat index chart

As you can see, the dangers of heat stroke and heat exhaustion can start to set in at temperatures as low as 80 degrees Fahrenheit. As humidity rises, you quickly get into the Extreme Caution and Danger zones.

Physical activity also contributes to your body’s ability to withstand high heat indexes. The more humid the air around you becomes, the more difficult it is for your sweat to evaporate and cool your body properly.


Heat Index – the silent killer

heat index sun

As noted in the article that accompanies the chart above, the heat index numbers were calculated assuming shady and light wind conditions. However, when we’re out hiking, working, and enjoying the outdoors, chances are we’re in direct sunlight and there may or may not be any wind. This can intensify heat index up to 15 degrees Fahrenheit. Your round of golf on the back nine just got a little riskier under the “right” conditions.

Additionally, it goes on to say that “strong winds, particularly with very hot, dry air, can be extremely hazardous.” This might sound contrary to what was just said about heat index, but having spent time in Death Valley, CA, I can tell you it’s true.

We all know that “dry heat” doesn’t feel as hot as “humid heat.” We also know that a light breeze can make us feel cooler too. So not only does the dry heat make us feel cool, but the breeze makes us feel cool, too; and both occurring at the same time makes us feel extra cool. It makes it easy to forget that we’re outside straining our bodies in 105 degree weather in direct sunlight. A quick look at the chart and we see that it only needs to be about 47% humidity and we’re in extreme danger. (Not to mention how much these conditions dehydrate our bodies, exacerbating the onset of heat exhaustion.)


Heat Index is everyone’s problem

It has become (or ‘still is,’ depending on how you view it) such a major issue this year that Drew Brees from the New Orleans Saints is taking part in a public awareness campaign and speaking about his experiences with it.



Tragically, there seems to be at least one high-profile death every year from athletes being exposed and not carefully monitored while practicing and playing in these conditions.

In 2001, Korey Stringer, a professional football player for the Minnesota Vikings, collapsed during training camp and never recovered. In 2011, a Dutch music promoter and his girlfriend died hiking in Joshua Tree National Park. In 2014, Dave Legeno, perhaps best known for his role in ‘Harry Potter,’ collapsed while hiking in Death Valley. In this 2009 article on Live Science, they cite an annual report from the University of North Carolina that states, “Since 1995, 33 football players have died from heat stroke.”


Don’t let heat index win

Now that you know what heat index is and just how dangerous it can be, here are a few tips to make sure you stay safe this summer:

Check the weather and use common sense

If it’s going to be 90 degrees and 75% humidity, you’re already in the danger zone. If you were planning to go on a 40 mile bike ride, see if you can postpone it a day or go in the evening when it’s cooler.

Seek shade, rest often

If you have to be out in Danger or Extreme Danger conditions, find as much shade as possible as frequently as possible. Don’t let your body heat up to the point you can’t cool it down naturally.

Drink a lot of water

By ingesting cool water, we can slightly decrease our core temperature momentarily. On top of that, making sure that we’re well hydrated ensures we have enough fluids to produce sweat (our bodies’ natural cooling mechanism).

Watch for signs of heat exhaustion

WebMD lists these common symptoms of heat exhaustion:

Throbbing headache
Dizziness and light-headedness
Lack of sweating despite the heat
Red, hot, and dry skin
Muscle weakness or cramps
Nausea and vomiting
Rapid heartbeat, which may be either strong or weak
Rapid, shallow breathing
Behavioral changes such as confusion, disorientation, or staggering


Carry an INO Weather Pro™

INO Weather Pro


We’re a bit biased, but we think this could solve a lot of problems for solo athletes, coaches, trainers, crew chiefs, and just about anyone that loves to be active or works outdoors. Not only does it provide temperature and humidity as separate measurements, but it does the heat index calculation for you and provides that as well.


Have fun and stay safe out there!