According to the National Weather Service, heat is the leading weather-related killer in the United States, resulting in hundreds of fatalities each year.

According to The Impacts Of Climate Change On Human Health In The United States: A Scientific Assessment the following groups are particularly vulnerable to heat; check in with friends and relatives who fall in one of these populations, especially if they don’t have air conditioning.

• Young children and infants are particularly vulnerable to heat-related illness and death, as their bodies are less able to adapt to heat than are adults.
• Older adults, particularly those who have pre-existing diseases, take certain medications, are living alone or have limited mobility who are exposed to extreme heat can experience multiple adverse effects.
• People with chronic medical conditions are more likely to have a serious health problem during a heat wave than healthy people.
• Pregnant women are also at higher risk. Extreme heat events have been associated with adverse birth outcomes such as low birth weight, preterm birth, and infant mortality, as well as congenital cataracts.¹

Each National Weather Service Forecast Office issues some or all of the following heat-related products as conditions warrant. NWS local offices often collaborate with local partners to determine when an alert should be issued for a local area. For instance, residents of Florida are much more prepared for 90°F+ weather than residents in Alaska.

Extreme Heat Warning—Take Action! An Extreme Heat Warning is issued when extremely dangerous heat conditions are expected or occurring. Avoid outdoor activities, especially during the heat of the day. If you must be outside, be sure to drink plenty of water and take frequent breaks in the shade. Stay indoors in an air-conditioned space as much as possible, including overnight. Check on family and neighbors.

Extreme Heat Watch—Be Prepared! An Extreme Heat Watch is issued when conditions are favorable for an extreme heat event but its occurrence and timing is still uncertain. Plan to suspend all major outdoor activities if a warning is issued. If you do not have air conditioning, locate the nearest cooling shelter or discuss staying with nearby family or friends who have air conditioning.

Heat Advisory—Take Action! A Heat Advisory is issued for dangerous heat conditions that are not expected to reach warning criteria. Consider postponing or rescheduling outdoor activities, especially during the heat of the day. If you must be outside, be sure to drink plenty of water and take frequent breaks in the shade. Stay in a cool place, especially during the heat of the day and evening.²

What is the Heat Index?

According to the National Weather Service, the heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature.  This has important considerations for the human body’s comfort.  When the body gets too hot, it begins to perspire or sweat to cool itself off.  If the perspiration is not able to evaporate, the body cannot regulate its temperature.  Evaporation is a cooling process.  When perspiration is evaporated off the body, it effectively reduces the body’s temperature.  When the atmospheric moisture content (i.e. relative humidity) is high, the rate of evaporation from the body decreases.  In other words, the human body feels warmer in humid conditions.  The opposite is true when the relative humidity decreases because the rate of perspiration increases.  The body actually feels cooler in arid conditions.  There is direct relationship between the air temperature and relative humidity and the heat index, meaning as the air temperature and relative humidity increase (decrease), the heat index increases (decreases).³

Use this weather calculator if you prefer to enter numbers manually instead of reading a chart.

 

¹“Heat Safety Tips and Resources.” National Weather Service, National Oceanic and Atmospheric Administration, https://www.weather.gov/safety/heat/

²“Understanding Heat Alerts.” National Weather Service, National Oceanic and Atmospheric Administration, https://www.weather.gov/safety/heat-ww

³“What is the heat index?” National Weather Service, National Oceanic and Atmospheric Administration, https://www.weather.gov/ama/heatindex