Nighttime Heat Dangers People Overlook

During a heat wave, much attention is paid to extremely high temperatures during the daytime, but it’s the warm overnight lows that can be really dangerous. Many think they'll get some relief as the sun goes down, but unfortunately, that is not always the case.

Why Are Overnight Lows Concerning?

Warm nighttime temperatures, especially 80 degrees or warmer, do not allow people to recover from daytime heat. When warm low temperatures are combined with high humidity, conditions can become dangerous, if not deadly, even in the middle of the night.

Without relief from the heat at night, heat stress can continue to build and increase the risk of heat illnesses and death. The elderly, children under 4 years old, those living in homes without air conditioners and people with chronic disease are at the highest risk.

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More people die from heat, on average, than any other weather hazard, based on the 10-year preliminary average from 2015-2024, according to NOAA. Over this 10-year period, there were an average of 238 heat deaths each year, many of which occurred during heat waves.

(MORE: What Is A Heat Advisory And Extreme Heat Warning?)

Urban Areas Face A Higher Risk

Those living in cities can be more prone to heat-related illnesses at night than their rural counterparts because of the so-called "urban heat island" effect.

Concrete and asphalt heats up rapidly during the day and then releases heat slowly at night, which can cause a difference in temperatures of up to 10 degrees or hotter in urban areas compared to nearby rural areas.

Couple the urban heat island effect with people's reluctance to open windows at night due to safety, and you have homes that can become like ovens.

Temperatures Aren’t The Only Concern

Did you know that humidity usually increases during the overnight hours?

This is because as the temperature falls, air is less able to "hold" water molecules the cooler it gets. This is often why it feels more damp at night, and why dew forms during the overnight hours.

When high temperatures and high dew points remain elevated during the night, our bodies attempt to perspire to cool off. However, when the perspiration does not evaporate because of the high humidity, the moisture clings to your body and body temperature can rise quickly, leading to heat exhaustion or heat stroke, according to the Mayo Clinic.

High heat, high humidity and a lack of fluids can rapidly lead to organ failure – sometimes within an hour.

(MORE: When Is The Hottest Day Where You Live?)

How To Stay Safe During A Heat Wave

The Centers for Disease Control and Prevention (CDC) offers a few tips to stay safe during heat waves: stay in air conditioning; take frequent breaks when outside; drink more water than usual; take cool showers or baths and wear lightweight and light-colored clothing.

At night, sticking a bowl of ice water in front of a fan and putting your sheets in the freezer for a few minutes before going to bed can make it easier to fall asleep. Don't let your sheets freeze, but do allow them to be cold to the touch. Additionally, you can wrap ice packs in cold, dry towels to help you stay cold at any time of the day or night.

Also, be sure to check on neighbors and friends, especially the elderly and those with health concerns, and always pay attention to the latest weather forecast to stay on top of any upcoming weather hazards.

Miriam Guthrie graduated from the Georgia Institute of Technology with an undergraduate degree in Atmospheric and Oceanic Sciences and is now a meteorology intern with weather.com before returning to school for her masters.