Heat is the top weather-related killer in the United States. Older adults, the sick, and the very young are most vulnerable to extreme heat.
During extreme heat, the best way to stay cool and safe is spend time in an air-conditioned environment. Be sure to check on older friends and relatives and never, ever leave a child or pet unattended in a parked car.
This page contains basic information about extreme heat events, heat safety, local cooling center information, and heat weather forecast information and data.
What is the difference between a heat watch, heat advisory, and heat warning?
An excessive heat watch (or simply heat watch) is issued by the National Weather Service when the forecast calls for heat indices above 105°F during the day and nighttime low temperatures of 80°F or higher for two consecutive days.
A heat advisory is issued when a significant heat event is expected within the next 36 hours. An excessive heat warning (or simply heat warning) is issued when conditions are dangerous to life or property, whereas the advisory indicates less serious, but still significant conditions that require caution, especially for the young and elderly.
What is the heat index?
The heat index measures the apparent temperature (the “feels like” factor) when relative humidity is factored into the air temperature. Higher humidity at the same temperature means a higher heat index.
The National Weather Service has a heat index calculator available here.
What’s the relationship between temperature and dew point?
The dew point is simply the temperature at which the air cannot hold all the moisture in it and dew begins to form. The higher the dew point, the more humid it is. The chart below relates dew point to how humid it feels.
How Humid it Feels (and subjective description)
|Below 55||Dry (Pleasant)|
|55-60||Hint of humidity (Still comfortable)|
|65-70||Sticky (Becoming unpleasant)|
|Above 75||Sultry (Oppressive and unbearable)|
Heat safety: During extreme heat…
(adapted from EPA Heat Guidebook)
• Use air conditioners or spend time in air-conditioned locations such as malls and libraries
• Use portable electric fans to exhaust hot air from rooms or draw in cooler air
• Take a cool bath or shower
• Minimize direct exposure to the sun
• Stay hydrated – regularly drink water or other nonalcoholic fluids
• Eat light, cool, easy-to-digest foods such as fruit or salads
• Wear loose fitting, light-colored clothes
• Check on older, sick, or frail people who may need help responding to the heat
• Know the symptoms of excessive heat exposure and the appropriate responses.
• Direct the flow of portable electric fans toward yourself when room temperature is hotter than 90°f
• Leave children and pets alone in cars for any amount of time
• Drink alcohol to try to stay cool
• Eat heavy, hot, or hard-to-digest foods
• Wear heavy, dark clothing.
Cooling Centers in the Washington, D.C. area
D.C. Homeland Security and Emergency Management Page (home page)
D.C. Cooling Center Locations (organized by ward)
Maryland cooling centers
Additional heat safety resources
National Weather Service
Environmental Protection Agency
Extreme Heat Homepage
The do’s and don’ts for dealing with extreme heat
Excessive Heat Events Guidebook: This resource, developed by the Environmental Protection Agency in partnership with NOAA and FEMA, is designed to help community officials, emergency managers, meteorologists, and others plan for and respond to excessive heat events.
Urban Heat Island Reduction Initiative
Federal Emergency Management Agency
Centers for Disease Control and Protection
The Humane Society
Heat data: What’s normal vs. extreme?
90 degree days in Washington, D.C.: Yearly, seasonal and monthly averages and extremes
What’s D.C. like in June? Breaking down norms and extremes
What’s D.C. like in July? Breaking down norms and extremes
What’s D.C. like in August? Breaking down norms and extremes
What are Washington, D.C.’s records for heat index and dew point?
Average and record temperatures for all three local airports (all months):
Records look-up: search daily, monthly and all-time record temperatures for any state in the U.S.
Air Quality Resources
Because DC heat waves are often accompanied by poor air quality, we have included useful links to understanding and monitoring the Air Quality Index (AQI):
Understanding the Air Quality Index
Map of current air quality conditions (NWS)
Map of current air quality conditions - Northeast U.S. (NWS)
AIRNow homepage (airnow.gov)
Washington, D.C. air quality forecast page (Metropolitan Council of Governments)
Sun safety information
Extreme heat is often accompanied by very high to extreme levels of ultraviolet (UV) radiation which causes sunburn, premature aging of the skin and is a risk factor for skin cancer and cataracts. Here are some useful links:
Capital Weather Gang heat features
Page compiled by Justin Grieser and Jason Samenow