Planning for and Responding to Extreme Heat

• Issue immediate public warnings when the National Weather Service issues a heat alert for your area or dangerously hot temperatures are forecasted.
• Share heat advisory alerts with the public through social media, local news outlets (radio/newspapers/TV) and community bulletin boards.
• Local public health and emergency managers should work together to ensure consistent messaging. Some groups may require targeted messaging.
• Chapter 3 of the Minnesota Extreme Heat Toolkit (PDF) has customizable communications to inform communities about the health risks of heat and how to stay safe. This includes:
  • Social media messages
  • Targeted messages to reach at-risk groups
  • Radio public service announcements (PSAs)
  • A sample news release

• Reach out to community partners to identify vulnerable groups.
• Existing disaster registries, such as Everbridge or OnSolve Code RED, can be critical resources to reach vulnerable populations.
• Coordinate with your local Public Health Preparedness Consultants (PHPCs) to help reach people listed in the disaster registries. Find PHPCs at Public Health Preparedness Consultants (PHPCs) | Minnesota Department of Health.

• A cooling center is a well-known community place, like a library or community center, that can be a safe, cool space for people to go to during extreme heat.
• Chapter 2 of the Minnesota Extreme Heat Toolkit (PDF) includes more information about setting up cooling centers, including:
  • Key considerations when choosing locations for cooling centers.
  • Tips to ensure cooling center access for vulnerable populations.

• Anticipate electricity disruptions due to an increased strain on the electrical grid.
• Plan for the possibility of a community-wide power outage lasting at least two days during a heat wave.
• Advise people to conserve energy.
• Chapter 2 of the Minnesota Extreme Heat Toolkit (PDF) has more information, such as what to ask the local utility provider.

Extreme heat is a term to describe weather that is much hotter and/or humid than typical for a time and place.

Extreme heat watches are issued when conditions are favorable for an extreme heat event in the next 24 to 72 hours. A watch is used when the risk of a heat wave has increased but its occurrence and timing is still uncertain. A watch provides enough lead time so that those who need to prepare can do so, such as city officials who have extreme heat response plans.

Heat advisories are issued when an extreme heat event is expected in the next 48 hours. These statements are issued when an extreme heat event is occurring, is imminent, or has a very high probability of occurring. An advisory is for less serious conditions that cause significant discomfort or inconvenience and, if caution is not taken, could lead to a threat to life and/or property.

Extreme heat warnings are issued when an extreme heat event is expected in the next 48 hours. These statements are issued when an extreme heat event is occurring, is imminent, or has a very high probability of occurring. A warning is used for conditions posing a threat to life and/or property.

The heat index is what the temperature feels like to the human body based on relative humidity and air temperature.

Wet-bulb globe temperature (WBGT) is a way to measure how heat affects the human body by combining temperature, humidity, sunlight, wind speed, and solar radiation into one number. Unlike regular temperature readings, WBGT gives us a better picture of how hot it feels and how hard it is for your body to cool itself. The most accurate way to measure WBGT is with on-site handheld meters, since wind and humidity can fluctuate over short distances. These meters can be purchased online or at many hardware, home improvement, and sporting goods stores. If a handheld meter is not available, your local NWS station can help with estimating the current WBGT in your precise area.

• Wet-Bulb Globe Temperature: How and When to Use It | National Weather Service.

Minnesota is projected to get hotter and more humid in the years ahead. According to the Minnesota State Climatology Office, an increase in days of extreme heat is being driven by an increase in days with high humidity.

Humidity is measured as the dew point, the temperature to which the air must be cooled at constant pressure for it to become saturated. The higher the dew point temperature, the greater the amount of moisture in the air.

People accustomed to continental climates (e.g., Minnesotans and Midwesterners generally) often begin to feel uncomfortable when the dew point temperature reaches between 65° F and 69° F. Dew points above 75° F are generally perceived as very uncomfortable or even oppressive by most residents in these areas. Higher dew point temperatures and humidity directly impact health by making it more difficult for people to cool themselves.

Health impacts from heat and humidity are preventable with appropriate public health responses, such as resting in an air-conditioned space, drinking water all day, and staying informed of local heat alerts.

• Dew Point vs. Humidity | National Weather Service