Skip to main content

Public Health extreme heat response


Heat is one of the leading weather-related causes of death in the United States, resulting in hundreds of fatalities each year. Extreme heat is defined as summertime temperatures that are much hotter than average for a particular climate.

For our region, it doesn’t take much additional heat to increase our risk of heat-related illnesses and cause other health impacts. Public Health – Seattle & King County developed its Extreme Heat Response Plan (357 Kb) to describe actions the department may take before and during an extreme heat event to protect community health and limit health disparities from extreme heat events. This page provides an overview of the risks facing our community, Public Health response actions and recommendations for preparedness and response professionals to support regional coordination across King County during an extreme heat event.

Health impacts and community risk factors

Heat affects everyone differently and some are more at risk than others due to individual factors and their environments.

  • What does extreme heat do to our bodies?

    Heat-related illnesses, like heat exhaustion or heat stroke, happen when the body is not able to properly cool itself. While the body normally cools itself by sweating, this might not be enough during extreme heat events. In these cases, a person's body temperature rises faster than it can cool itself down. This can cause damage to the brain and other vital organs.

  • What increases risk of heat-related illnesses?

    Underlying health conditions, certain medications and drug use, and individual factors and determinants such as age, employment, housing status, and outdoor activity levels may increase an individual’s vulnerability to heat-related illness.

    Those more sensitive to heat include: children and older adults; outdoor workers; individuals experiencing homelessness or living unsheltered; households without access to cooling resources; athletes and people who exercise outdoors; and people with chronic health conditions, including mental health conditions.

  • What environmental factors can increase health risks from extreme heat in King County?

    • Temperate Climate: With a historically mild temperate climate, King County residents are generally not acclimated to high temperatures. Acclimatization can begin to be lost after about one week away from working or living in hotter climates. After one month of away from consistent heat, most people’s tolerance will return to baseline.
    • Urban Heat Islands: Dense urban areas with a lot of paved surfaces and limited shade can be up to 20°F hotter during extreme heat events, when compared to areas with more trees and less pavement. A 2020 heat mapping project of King County revealed that many of these “urban heat island” areas have also been disproportionality affected by other health inequities.
    • Built Environment: Many homes in King County do not have air conditioning and are built with south- and west-facing windows, increasing the intensity of heat people may experience indoors during extreme heat events. As sunlight enters uncovered windows, heat gets absorbed into buildings. Without air conditioning to cool things down, or using curtains or other methods to block sunlight from entering, homes and buildings can overheat and become hotter than outside temperatures. This indoor heat can also linger much later into the night.

Responding to extreme heat

Guidance for response partners

The National Weather Service (NWS) can issue an Excessive Heat Warning, Excessive Heat Watch, or Heat Advisory ahead of a heat event. When any of these are released, Public Health recommends response agencies and jurisdictions use the NWS’ HeatRisk forecast and the Public Health Recommended Heat Measures to inform appropriate response actions to take based on the forecasted heat event and its associated risk.

Recommended actions are aligned with each HeatRisk value, focusing on measures to support those most at risk from extreme heat.

NWS HeatRisk Values

Public Health Recommendations



  • Recommend sharing information about available cooling locations where general population can go to access air conditioning or cooling features such as water recreation facilities or other public places
  • Recommend dissemination of key public health heat safety messaging and risk communications to at-risk populations, including those experiencing homelessness, older adults, children, and outdoor workers
  • Consider limiting strenuous outdoor activities during the hottest period of the day
  • Consider cancellation and/or rescheduling of outdoor children’s activities, day-camps, athletic practice, and games taking place during the hottest period of the day or consider moving them indoors where temperatures are cooler
  • Consider distribution of water and other cooling supplies for at-risk communities and populations
  • Consider activation of daytime cooling centers for unsheltered individuals
  • Consider undertaking preparation activities required to meet recommendations of higher HeatRisk levels, if forecast indicates increase in risk and temperatures
  • Monitor NWS HeatRisk forecast and alerts until forecast conditions become more favorable (e.g., HeatRisk Value of 1 - yellow - or lower)



  • Continue outreach efforts to reach at-risk populations with risk communications, cooling supplies, and water resources
  • Recommend activation of daytime cooling centers for unsheltered individuals
  • Recommend activation of daytime cooling centers for general population
  • Recommend temporary suspension of strenuous outdoor activities during hottest times of the day
  • Recommend cancellation and/or rescheduling of outdoor children’s activities, day-camps, athletic practice, and games
  • Recommend conducting wellness checks on elders and people living with disabilities to ensure access to air conditioning or cooling centers
  • Consider expanding hours of operation for cooling centers for unsheltered individuals to accommodate overnight use
  • Consider capabilities of schools to maintain cooler indoor air temperatures if school is in session; Public Health will recommend closure if indoor temperatures cannot be maintained reasonably free of excessive heat (WAC § 246-366-080)



  • Recommend expanding hours of operation for cooling centers to accommodate overnight use
  • Recommend cancellation of outdoor activities and events during hottest times of the day

Public Health response

Public Health also takes action based on the NWS’ alerts and the forecasted HeatRisk for King County. When Public Health receives an alert, it triggers response activities, including:

  • Public information, messaging, and community outreach: Public Health produces health messaging on how to stay safe in high temperatures. This messaging prioritizes information for populations who are at highest risk from heat-related illnesses due to exposure levels, age, or other risk factors. Information may go out through social media, partner channels, blogs, and the media. Through the work of Public Health’s Healthcare for the Homeless Network, and in partnership with King County Regional Homelessness Authority, outreach is conducted to connect individuals experiencing homelessness with information and available resources.
  • Data and surveillance: Public Health begins collecting data on heat-related impacts to the community, including: heat-related visits to emergency departments; emergency calls and drowning events; and heat-related deaths. This data is shared with the public and partners and used to inform future response efforts.
  • Heat health and safety guidance: During extreme heat events, Public Health shares recommendations and guidance with response partners to better align efforts at messaging, opening cooling centers, and reducing outdoor activities. Public Health may also share additional existing guidance to support key partners in their decision-making, such as employers with outdoor workers.

Public Health conducts additional response activities to help maintain situational awareness and response coordination across the department throughout the heat event.

Keeping plans relevant

The Extreme Heat Response Plan is reviewed prior to each summer season to ensure Public Health’s guidance remains accurate and response activities continue to protect community health and limit health disparities in the face of increasing extreme weather events. The revision process includes engagement and feedback from across Public Health programs, response partners, and impacted communities.