Eco-Explainer: What is the Difference Between a Heat Advisory and a Heat Warning?

Feeling the heat? Learn how heat alerts can help you beat it and protect your health.

While walking in the heat of the summer lately, you may feel that the air is so thick it can be cut with a knife! Not only is the temperature hot, but the moisture in the air adds another layer of overwhelm that can make it feel harder to get through the day.

What are heat advisories and heat warnings?

You may be checking the weather on your app daily or watching the local weather station before heading out to work in the morning. Understanding the differences in heat alerts will help you better prepare for those sweltering summer days.

Climate Central’s Vice President for Science, Dr. Kristina Dahl, explains that the two main heat alerts are on along a continuum:

• Heat advisories inform the public that the heat index will be high, but do not meet the criteria for an Excessive Heat Warning.
• Heat warnings, in particular, Excessive Heat Warnings, indicate that people need to take precautions to protect themselves from the dangerous heat levels.

Interestingly, each NWS Weather Forecast Office can set its own criteria for heat alerts based on its regional weather patterns; for example, a heat advisory in Texas may be considered an extreme heat warning in Maine. 

Dr. Dahl mentioned that the city of Philadelphia is ahead of the game when it comes to providing resources and messages to its residents. She refers to the 2015 collaborative initiative between the Philadelphia Department of Public Health (PDPH) and the NWS, which was established to address the increasing number of heat-related health issues in the city. Philadelphia has been a city that has taken a more systematic approach to addressing these concerns compared to other parts of the country.

Nationally, the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service (NWS) have recently experienced significant budget and staffing cuts. Nearly 600 NWS positions have been eliminated, and NOAA is at risk of closing critical research labs, which can result in receiving less timely and accurate heat and other weather-related alerts.

Why is it so muggy?

Dr. Dahl discusses that the hot and muggy feel to the air is primarily driven by the rise in temperatures, rather than shifts in rainfall patterns. Over the past 50-70 years in the Mid-Atlantic region of the United States, there has been a significant increase in heavy downpours, leading to more frequent flooding. The rising temperatures and rainfall are two factors of the same problem: a warming planet.

Who’s most at risk during extreme heat?

Human activities, including shifts in manufacturing and the use of fossil fuels, contribute to climate change, the cause of longer hot seasons. In Philadelphia, this means excessive heat leading into the fall months and longer heatwave durations.

Dr. Dahl explains that this significance is particularly evident in cities experiencing more extreme summers, where the use of building materials and land clearing can lead to areas within cities suffering from heat known as heat islands.

The EPA defines a heat island as an urban area with higher temperatures than its surrounding areas. The cause of heat islands is due to less green landscape, building structures, and infrastructure absorbing and re-emitting the sun’s heat into the atmosphere.

In terms of groups that are more at risk during extreme heat, Dr. Dahl explains that everyone is susceptible to heat, but the level of exposure and vulnerability differs.

“If you live in a more urban area, you are more exposed to heat, have fewer trees, and are subject to the overall infrastructure.”

Heat vulnerability is significant as well. Vulnerable neighborhoods that were historically redlined were due to racism and discriminatory practices. Oftentimes, these are communities of people of color and lower-income earners. The scarcity of green spaces and limitations to cooling systems leave these communities more susceptible to more extreme heat than whiter suburban areas.”

How can you stay safe when heat alerts are issued?

Oftentimes, the heat isn’t considered an extreme weather condition. Dr. Dahl explains that heat is considered a “silent killer” because it doesn’t get the same attention as more devastating weather events such as hurricanes or wildfires. Generally, heat is not talked about with as much urgency. There is almost an unspoken expectation of resilience when it comes to people being able to manage the heat. In order to remain safe during extreme heat, it requires us to think differently about heat.

Make mindful choices and adjustments during extreme heat events to help prevent heat-related illnesses including:

• Take a break from tending to your garden and wait to go outside once the heat warning has passed.
• Take an air-conditioned public bus or train home, instead of walking or biking.
• Track the hotter parts of the city that you live in using the following tools provided by Climate Central:
  • Urban Heat Islands interactive maps (you can choose a city with a dropdown menu at the top of the page)
  • Changes in summertime temperatures (clicking on these graphics will take you to a page where you can generate city-specific graphics)
• Utilize the city’s free resources for pools, libraries, and other cooling centers.

Photo by Keith McCrea on Unsplash