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Flash Flood Risk in the Mid-Atlantic; Storms in the High Plains; Critical Fire Weather Threats in the West

Heavy rain and thunderstorms will pose a flash flood risk for the Mid-Atlantic. Severe thunderstorms are possible through Friday from the northern and central Plains to the Upper Midwest. Elevated and critical fire weather conditions with isolated dry thunderstorm potential across a large part of the West. Above average temperatures are expected in the Southern Plains and Northeast. Read More >

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Heat & Humidity Dangers

Summer Weather Safety and Survival

The Dangers of Heat and Humidity

It has been said that "It's not the heat, it's the humidity". Well, actually it's both. Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and-as the last extremity is reached-by panting, when blood is heated above 98.6 degrees. The heart begins to pump more blood, blood vessels dilate to accommodate the increased flow, and the bundles of tiny capillaries threading through the upper layers of skin are put into operation. The body's blood is circulated closer to the skin's surface, and excess heat drains off into the cooler atmosphere. At the same time, water diffuses through the skin as perspiration. The skin handles about 90 percent of the body's heat dissipating function.

Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation--and high relative humidity retards evaporation. The evaporation process itself works this way: the heat energy required to evaporate the sweat is extracted from the body, thereby cooling it. Under conditions of high temperature (above 90 degrees) and high relative humidity, the body is doing everything it can to maintain 98.6 degrees inside. The heart is pumping a torrent of blood through dilated circulatory vessels; the sweat glands are pouring liquid-including essential dissolved chemicals, like sodium and chloride onto the surface of the skin.

Heat disorders generally have to do with a reduction or collapse of the body's ability to shed heat by circulatory changes and sweating, or a chemical (salt) imbalance caused by too much sweating. When heat gain exceeds the level the body can remove, or when the body cannot compensate for fluids and salt lost through perspiration, the temperature of the body's inner core begins to rise and heat-related illness may develop.

DID YOU KNOW...

  • In a normal year, approximately 175 Americans die from extreme heat. Young children, elderly people, and those who are sick or overweight are more likely to become victims.

  • Between 1936 and 1975, nearly 20,000 people succumbed to the effects of heat and solar radiation.

  • Because men sweat more than women, men are more susceptible to heat illness because they become more quickly dehydrated.

Knowing how the body deals with excessive heat is critical in understanding the dangers to you and proper steps to take to prevent becoming a victim of excessive heat.