In recent years, excessive heat has caused more deaths than all other weather events, including floods. The American Meteorological Society reports that on average heat kills more than 1,000 people each year. During the July 1995 heat wave in Chicago, more than 700 people died as a result of excessive heat.
Heat kills by pushing the human body beyond its limits. Under normal conditions, the body's internal thermostat produces perspiration that evaporates and cools the body. However, in extreme heat and high humidity, evaporation is slowed and the body must work extra hard to maintain normal body temperatures.
What is a heat wave?
A heat wave is a prolonged period of excessive heat, often combined with excessive humidity. Generally, excessive heat is defined as temperatures that hover 10 degrees or more above average high temperature for the region during summer months, last for a prolonged period of time, and often are accompanied by high humidity.
What is the heat index?
The heat index is the temperature the body feels when the effects of heat and humidity are combined. Exposure to direct sunlight can increase the heat index by up to 15 degrees.
What are heat cramps, heat exhaustion, heatstroke, and sunstroke? Heat cramps are muscular pains and spasms caused by heavy exertion in high heat. Heat cramps are often the first sign that the body is having trouble with the heat.
Heat exhaustion typically involves the loss of body fluids through heavy sweating when someone strenuously exercises or works in high heat and humidity. In someone suffering heat exhaustion, blood flow to the skin increases while blood flow to vital organs decreases, resulting in a mild form of shock. If not treated, body temperature will continue to rise and the person may suffer heatstroke.
Heatstroke (also known as sunstroke) is a life-threatening condition in which a person's temperature control system, which produces sweating to cool the body, stops working. The body temperature of someone suffering from heatstroke can rise so high that brain damage and death may result if the body is not cooled quickly.
Watch, Warning, Advisory, Awareness
The National Weather Services issues alerts for excessive heat on a county-by-county basis. The alerts are broadcast on NOAA Weather Radio and on local radio and television stations. In Michigan the values at which warnings and advisories are necessary are based on the Heat Index and not the ambient air temperature.
Excessive Heat Watch means conditions are favorable for an event to meet or exceed local excessive heat warning criteria in the next 12 to 48 hours.
Excessive Heat Warning means that the threat is imminent or the National Weather Services has a very high confidence of meeting the warning criteria.
Excessive Heat Awareness means a heat index of 95 - 99 degrees is expected or ongoing.
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