Summertime heat is not often looked at as a major threat; it just does not cause the destruction like tornadoes, floods, or hurricanes. But in reality, excessive heat is deadly, killing more than a hundred Americans per year. That is more than hurricanes, lightning, tornadoes and flooding.

What is the Heat Index?

The Heat Index provides a way to estimate how warm the air feels to exposed skin. It includes the effects of both temperature and moisture.
The amount of moisture is important because evaporation of water from your skin and the resulting cooling of your body is less on humid days than on dry ones.
Meteorologists use the dew point to measure how much water vapor is present in the atmosphere. For example, when the dew point is 70 degrees the atmosphere has more than twice as much water vapor than when the dew point is 50 degrees.
The Heat Index was designed for shaded areas. When you are in full sunshine, exposed skin can feel up to 15 degrees warmer than the current Heat Index value.

See the graphic in the upper right corner for a chart of heat wave values.

What are some of the deadliest and most well-known heat waves in the U.S.?

A June-September 1980 heat wave in the central and eastern U.S. killed an estimated 1,750 people, including 1,250 in the city of St. Louis alone.
A July 1995 Midwest heat wave killed nearly 600 people over a five-day period in Illinois, mainly in Chicago. Temperatures there reached 106 degrees on July 13 and did not fall below 80 degrees for two consecutive nights.
A late-July, 2006 heat wave hit most of the U.S., killing at least 225 people.

What alerts does the National Weather Service issue during heat waves?

An EXCESSIVE HEAT WATCH is issued when the Heat Index will equal or exceed 105 degrees for 3 hours or more during the day, and remain at or above 80 degrees at night for two consecutive days.
A HEAT ADVISORY is issued about 12 hours in advance when the Heat Index will equal or exceed 105 degrees, but less than 115 degrees, for less than 3 hours during the day, and remain at or above 80 degrees at night for two consecutive days.
An EXCESSIVE HEAT WARNING is issued about 12 hours in advance when the Heat Index will equal or exceed 105 degrees for more than 3 hours or equal or exceed 115 degrees for any period during two consecutive days.

What special alerts does the National Weather Service issue for urban areas?

A new system, Heat/Health Watch/Warning, is in place for certain urban areas. So far, Dallas/Fort Worth; Phoenix; Yuma, Ariz.; Philadelphia; Chicago; St. Louis; Cincinnati/Dayton; New Orleans; Little Rock, Ark.; Memphis, Tenn.; Shreveport, La., Lake Charles, La.; Jackson, Miss.; Seattle, and Portland all use this system. It is designed with custom rules based on the city`s climatology. Check with your local NWS office for local alert rules.

For instance, Seattle`s system issues a Heat and Health Watch if daytime highs are expected to reach the 90s.

What are the signs of heat emergencies and how should they be treated?

Signs:

Heat cramps: Muscular pains and spasms due to heavy exertion. Although heat cramps are the least severe, they are an early signal that the body is having trouble with the heat. Heat cramps occur when the heat index is above 90 degrees.
Heat exhaustion: Cool, moist, pale, or flushed skin; heavy sweating; headache; nausea or vomiting; dizziness; and exhaustion. Body temperature will be near normal. Heat exhaustion occurs when index values are above 90 degrees and is likely to occur when the value is more than 105 degrees.
Heat stroke: Hot, red skin; changes in consciousness; rapid, weak pulse; and rapid, shallow breathing. Body temperature can be as high as 105 degrees F. If the person was sweating from heavy work or exercise, skin may be wet; otherwise, it will feel dry. Heat stroke occurs when index values are above 105 degrees.

Treatment:

Heat cramps: Get the person to a cooler place and have him or her rest in a comfortable position. Lightly stretch the affected muscle and replenish fluids. Give a half glass of cool water every 15 minutes. Do not give liquids with alcohol or caffeine in them, as they can make conditions worse.
Heat exhaustion: Get the person out of the heat and into a cooler place. Remove or loosen tight clothing and apply cool, wet cloths, such as towels or sheets. If the person is conscious, give cool water to drink. Make sure the person drinks slowly. Give a half glass of cool water every 15 minutes. Do not give liquids that contain alcohol or caffeine. Let the victim rest in a comfortable position, and watch carefully for changes in his or her condition.
Heat stroke: Heat stroke is a life-threatening situation. Help is needed fast. Call 9-1-1 or your local emergency number. Move the person to a cooler place. Quickly cool the body. Immerse victim in a cool bath, or wrap wet sheets around the body and fan it. Watch for signals of breathing problems. Keep the person lying down and continue to cool the body any way you can. If the victim refuses water or is vomiting or there are changes in the level of consciousness, do not give anything to eat or drink.

What precautions should you take during hot weather?

Slow down. Strenuous activities should be reduced, eliminated, or rescheduled to the coolest time of the day, usually early-morning or in the evening. Individuals at risk should stay in the coolest available place, not necessarily indoors.
Dress for summer. Lightweight, light-colored, loose-fitting clothing reflects heat and sunlight, and helps your body maintain normal temperatures.
Put less fuel on your inner fires. Foods (like proteins) that increase metabolic heat production also increase water loss.
Drink plenty of water or other nonalcoholic fluids and do not drink alcoholic beverages. Your body needs water to keep cool. Drink plenty of fluids even if you don`t feel thirsty. Persons who (1) have epilepsy or heart, kidney, or liver disease, (2) are on fluid restrictive diets, or (3) have a problem with fluid retention should consult a physician before increasing their consumption of fluids.
Do not take salt tablets unless specified by a physician. Persons on salt restrictive diets should consult a physician before increasing their salt intake.
Spend more time in air-conditioned places. Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned place like a movie theatre, mall or senior citizen center.
Don`t get too much sun. Sunburn makes the job of heat dissipation that much more difficult.

Heat Wave Safety Tips