Heat is more than just the temperature shown on a thermometer

The heat index, also called the “feels like” temperature, combines:

• Air temperature
• Humidity
• High humidity makes it harder for the body to sweat and cool itself effectively.
• As heat stress increases, it can lead to:Dehydration
• Electrolyte imbalances
• Heat cramps
• Heat exhaustion
• Heat stroke
• Heat-related illnesses are largely preventable with appropriate precautions.

What is the heat index?

The heat index measures how hot conditions feel by considering both temperature and humidity.
High humidity can make hot weather feel significantly more intense.
For example, 90°F (about 32°C) with 70% humidity can feel like 106°F (about 41°C).
The heat index was developed from work by physicist Robert Steadman in 1979.
The U.S. National Weather Service later developed its own heat-index calculation based on his work.

Why the heat index may need updating

Steadman’s original calculations had limitations at very high temperatures.
His model assumed sweat would continue accumulating on the skin, rather than dripping off the body.
Researchers say this becomes particularly important during extreme heat waves.
Alternative calculations used for very hot conditions may underestimate how hot conditions actually feel.
Researchers Yi-Chuan Lu and David Romps revisited Steadman’s work and proposed extending the calculations to higher temperature and humidity ranges.
Their example:
100°F (about 38°C) + 65% humidity
Current NWS index: 136°F (58°C)
Their proposed calculation: 153°F (67°C)

How to stay safe when the heat index is high

• Drink plenty of water and electrolyte fluids.
• Take regular breaks in the shade or air conditioning.
• Wear clothing appropriate for hot weather.
• Avoid the peak heat from midday through late afternoon.
• Check on:
• Older adults
• Young children
• People without reliable air conditioning
• Watch for signs of heat illness, including:
• Muscle cramps
• Headache
• Dizziness
• Excessive vomiting
• Shortness of breath

Heat stroke is a medical emergency and can cause confusion, seizures, or loss of consciousness.
If someone is experiencing severe heat illness, seek emergency medical help and begin cooling them while waiting for assistance.