Man, It’s Hot, Part 1: Summer Heat Risks

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We’re haven’t yet reached the first day of summer, but a major heat wave is expected to strike parts of the Midwest and Northeast for several days this week.  Record high temperatures are predicted to hit dozens of major cities from Iowa to New Hampshire.

Unlike a typical occasional hot day, the forecast heat wave is likely to linger for a week, with some areas having to deal with uncomfortable (and  possibly dangerous) temperatures for two weeks or more. Indeed, it may be the longest heat wave experienced in the regions in decades.Heat dome from prolonged high pressure front

Extended regions of high pressure that aren’t expected to move quickly through an area can cause the formation of a “heat dome,” A heat dome is a slow-moving or stationary high pressure system that helps create and encase heat, kind of like a lid on a boiling pot (except the pot is Cleveland).

Source: Fox Weather


2024 is the first year that the Centers for Disease Control (CDC) and The National Weather Service (NWS) will measure the health implication from hot weather using a new tool called “Heat Risk.” Heat Risk is a color-numeric index that forecasts the risk of heat-related impacts to occur over a 24-hour period. Heat Risk takes into consideration:

  • How unusually high the air temperature is during the 24-hour period.
  • The duration of the high temperatures, including both daytime and nighttime temperatures.
  • If the high temps pose an increased risk, per the CDC, of heat-related impacts.


GREEN (0):       Little or no risk from expected heat.

YELLOW: (1);   Minor – This heat level affects mostly those people extremely sensitive to heat, especially when outdoors without an effective cooling method or adequate hydration.

ORANGE (2):   Moderate – This heat level affects most individuals sensitive to heat, especially those without effective cooling methods or adequate hydration. Impacts begin in certain health systems and heat-sensitive industries.

RED (3):           Major – This level of heat affects even non-heat senstive people if they don’t have an effective cooling method and/or adequate hydration. Impacts likely in some health systems, heat-sensitive industries. Infrastructure begins to be affected.

MAGENTA (4): Extreme – High heat levels of long-duration with little to no overnight relief. Affects anyone without an effective cooling method and/or adequate hydration. Impacts likely in most health systems, heat-sensitive industries, and infrastructure.

Instituted by the National Oceanic and Atmospheric Administration (NOAA), the Heat Risk hopes to provide guidance to municipalities and other decision-makers with regards to actions needed to help prevent bad outcomes. Heat Risk is not the same as the Heat Index, which takes into account temperature combined with humidity.

Here’s what a Heat Risk map may look like:

Source: NOAA

The Heat Risk hopes to provide guidance to municipalities and other decision-makers with regards to actions needed to help prevent bad health outcomes in the local population.


You’ll hear on weather channels that the heat index is high, but why is the Heat Index even more important than air temperature? Above 60% relative humidity, loss of heat by perspiration is impaired. Exposure to full sun increases the reported heat index by as much as 10-15 degrees F. That means that high humidity and a temperature of 90 degrees Fahrenheit could feel like 105 degrees! All this increases the chances of heat-related illness.

Source: NOAA

Expect the power grid to be challenged by tens of millions of air conditioning units set on “high”, and we can expect to see some major health issues if the electricity goes out and people have to fight the heat with hand fans, like they did in the “good old days”.

the “good old days”

Urbanizations of the American landscape since the “good old days” hasn’t helped. The formations of “heat islands” in cities cause the development of  higher temperatures than outlying areas. Structures such as buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests and water bodies.

You might not consider a heat wave to be an actual natural disaster, but it most certainly is. Heat waves can cause mass casualties, as they did in Europe when tens of thousands died of exposure (not in the Middle Ages, but in 2003, due to widespread lack of air-conditioning). Places like India, Pakistan, and other underdeveloped countries in tropical zones experience thousands of heat-related deaths yearly. It’s important to know how to deal with heat-related illness in good times or bad.

Next time, we’ll discuss exactly how heat kills a person, the various types of heat-related illness like heat exhaustion, heat stroke, and more. We’ll also discuss the proper way to treat heat emergencies.

For part 2 of this article, click here:

Joe Alton MD

Dr. Alton and friend


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