Heat is the number one weather-related killer in the United States.The National Weather Service statistical data shows that heat causes more fatalities per year than floods, lightning, tornadoes and hurricanes combined. Based on the 10-year average from 2000 to 2009, excessive heat claims an average of 162 lives a year. By contrast, hurricanes killed 117; floods 65; tornadoes, 62; and lightning, 48.

In the disastrous heat wave of 1980, more than 1,250 people died. In the heat wave of 1995more than 700 deaths in the Chicago area were attributed to heat. In August 2003, a record heat wave in Europe claimed an estimated 50,000 lives.

North American summers are hot; most summers see heat waves in or more parts of the United States. East of the Rockies, they tend to combine both high temperature and high humidity, although some of the worst heat waves have been catastrophically dry. Additional detail on how heat impacts the human body is provided under "The Hazards of Excessive Heat" heading.

NOAA's Watch, Warning, and Advisory Products for Extreme Heat

Each National Weather Service (NWS) Weather Forecast Office (WFO) can issue the following heat-related products as conditions warrant:

Excessive Heat Outlook: are issued when the potential exists for an excessive heat event in the next 3-7 days. An Outlook provides information to those who need considerable lead time to prepare for the event, such as public utilities, emergency management and public health officials.

Excessive Heat Watch: is issued when conditions are favorable for an excessive heat event in the next 12 to 48 hours. A Watch is used when the risk of a heat wave has increased, but its occurrence and timing is still uncertain. A Watch provides enough lead time so those who need to prepare can do so, such as cities who have excessive heat event mitigation plans.

Excessive Heat Warning/Advisory are issued when an excessive heat event is expected in the next 36 hours. These products are issued when an excessive heat event is occurring, is imminent, or has a very high probability of occuring. The warning is used for conditions posing a threat to life or property. An advisory is for less serious conditions that cause significant discomfort or inconvenience and, if caution is not taken, could lead to a threat to life and/or property.

How Forecasters Decide Whether to Issue Excessive Heat Products

NOAA's heat alert procedures are based mainly on Heat Index Values. The Heat Index, sometimes referred to as the apparent temperature and given in degrees Fahrenheit, is a measure of how hot it really feels when relative humidity is factored with the actual air temperature.

To find the heat index, look at the Heat Index Chart. As an example, if the air temperature is 96°F (found on the top of the table) and the relative humidity is 65% (found on the left of the table), the heat index--how hot it feels--is 121°F. The National Weather Service will initiate alert procedures when the Heat Index is expected to exceed 105°- 110°F (depending on local climate) for at least 2 consecutive days.

IMPORTANT: Since heat index values were devised for shady, light wind conditions, exposure to full sunshine can increase heat index values by up to 15°f. also, strong winds, particularly with very hot, dry air, can be extremely hazardous.

The Heat Index Chart shaded zone above 105°F shows a level that may cause increasingly severe heat disorders with continued exposure and/or physical activity.

The Hazards of Excessive Heat

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 the body heats to quickly to cool itself safely, or when you lose much fluid or salt through dehydration or sweating, your body temperature rises and heat-related illness may develop. Heat disorders share one common feature: the individual has been in the heat too long is exercised too much for his or her age and physical condition.

Studies indicate that, other things being equal, the severity of heat disorders tend to increase with age. Conditions that cause heat cramps in a 17-year-old may result in heat exhaustion in someone 40, and heat stroke in a person over 60.

Sunburn, with its ultraviolet radiation burns, can significantly retard the skin's ability to shed excess heat.

Acclimatization has to do with adjusting sweat-salt concentrations, among other things. The idea is to lose enough water to regulate body temperature, with the least possible chemical disturbance/salt depletion.

Children, Adults and Pets Enclosed in Parked Vehicles Are at Great Risk

Each year children die from hyperthermia as a result of being left in parked vehicles. Hyperthermia is an acute condition that occurs when the body absorbs more heat than it can dissipate. Hyperthermia can occur even on a mild day. Studies have shown that the temperature inside a parked vehicle can rapidly rise to a dangerous level for children, adults and pets.  Leaving the windows slightly open does not significantly decrease the heating rate. The effects can be more severe on children because their bodies warm at a faster rate than adults.

Shown below is a time lapse photo of a thermometer reading in a car over a period of less than an hour. As the photograph shows, in just over 2 minutes the call went from a safe temperature to 94.3 degree F. These photos demonstrate just how quickly a vehicle can become a death trap for a child.

Hyperthermia deaths aren't confined to summer months. They also happen during the spring and fall. Below are some examples.

• Honolulu, HI, March 07, 2007: A 3-year-old girl died when the father left her in a child seat for an 1.5 hours while he visited friends in a Makiki apartment building.  The outside temperature was only 81 degrees. 
• North Augusta, SC, April 2006: A mother left her 15 month old son  in a car. He was in a car for 9 hours while his mom went to work. She is now serving a 20-year prison sentence.
• Denver, CO, August 2008: Two kids that died in an overheated car may have been on their own for more than 3 hours as their mother slept after working a night shift.  The kids died in a closed but unlocked car. Investigators believe the temperature in the car may have reached 123 degrees F.

Adults are in danger too. On July 12, 2001, a man died of heatstroke after falling asleep in his car with the windows rolled up in the parking lot of a supermarket in Hinds County, MS.

How Fast Can the Sun Heat A Car?

The atmosphere and the windows of a car are relatively “transparent” to the sun’s shortwave radiation (yellow in figure below) and are warmed little. This shortwave energy, however, does heat objects it strikes. For example, a dark dashboard or seat can easily reach temperatures in the range of 180 to more than 200 degrees F.

These objects (e.g., dashboard, steering wheel, childseat) heat the adjacent air by conduction and convection and also give off longwave radiation (red) which is very efficient at warming the air trapped inside a vehicle.

Objects Heated by the Sun Warm Vehicle's Air

CLICK HERE FOR ANIMATION (700K)
( Hi-Res ~ 2.5 mb.WMV file)
Individual Frames:
0 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min
(Animation Courtesy of General Motors and Golden Gate Weather Services)

Heat Safety

Child Safety Tips

• Make sure your child's safety seat and safety belt buckles aren't too hot before securing your child in a safety restraint system, especially when your car has been parked in the heat.
• Never leave your child unattended in a vehicle, even with the windows down.
• Teach children not to play in, on or around cars.
• Always lock car doors and trunks--even at home--and keep keys out of children's reach.
• Always make sure all children have left the car when you reach your destination. Don't leave sleeping infants in the car ever!

Adult Heat Wave Safety Tips

• Slow down. Reduce, eliminate or rescheduled strenuous activities until the coolest time of the day. Children, senior and anyone with health problems should stay in the coolest available place, not necessarily indoors.
• Dress for summer. Wear lightweight, light-colored clothing to reflect heat and sunlight.
• Put less fuel on your inner fires.Foods, like meat and other proteins that increase metabolic heat production also increase water loss.
• Drink plenty of water or other non-alcohol or decaffeinated fluids.Your body needs water to keep cool. Drink plenty of fluids even if you don't feel thirsty. Persons who have epilepsy or heart, kidney, or liver disease, are on fluid restrictive diets or have a problem with fluid retention should consult a physician before increasing their consumption of fluids. Do not drink alcoholic beverages and limited caffeinated beverages.
• During excess heat period, 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, go to a library, store or other location with air conditioning for part of the day.
• Don't get too much sun. Sunburn reduced your body's ability to dissipate heat.
• Do not take salt tablets unless specified by a physician.

Heat Disorder Symptoms

SUNBURN: Redness and pain. In severe cases swelling of skin, blisters, fever, headaches. First Aid: Ointments for mild cases if blisters appear and do not break. If breaking occurs, apply dry sterile dressing. Serious, extensive cases should be seen by physician.

HEAT CRAMPS: Painful spasms usually in the muscles of legs and abdomen. Heavy sweating. First Aid: Firm pressure on cramping muscles or gentle massage to relieve spasm. Give sips of water. If nausea occurs, discontinue water.

HEAT EXHAUSTION: Heavy sweating, weakness, skin cold, pale and clammy. Pulse thready. Normal temperature possible. Fainting and vomiting. First Aid:Get victim out of sun. Once inside, the person should lay down and loosen clothing. Apply cool, wet cloths. Fan or move victim to air conditioned room. Offer sips of water. If nausea occurs, discontinue water. If vomiting continues, seek immediate medical attention.

HEAT STROKE (or sunstroke): High body temperature (106° F or higher). Hot dry skin. Rapid and strong pulse. Possible unconsciousness. First Aid: HEAT STROKE IS A SEVERE MEDICAL EMERGENCY. SUMMON EMERGENCY MEDICAL ASSISTANCE OR GET THE VICTIM TO A HOSPITAL IMMEDIATELY. DELAY CAN BE FATAL. White waiting for emergency assistance, move the victim to a cooler environment Reduce body temperature with cold bath or sponging. Use extreme caution. Remove clothing, use fans and air conditioners. If temperature rises again, repeat process. Do not give fluids. Persons on salt restrictive diets should consult a physician before increasing their salt intake.

For more information contact your local American Red Cross Chapter. Ask to enroll in a first aid course.

Community Guidance: Preparing for and Responding to Excessive Heat Events

The Excessive Heat Events Guidebook was developed by the Environmental Protection Agency (EPA) in 2006, in collaboration with the National Weather Service, the Centers for Disease Control and Prevention, and theDepartment of Homeland Security. This guidebook provides best practices for saving lives during heat waves in urban areas, and provides a menu of options that communities can use in developing their own mitigation plans. Beat the Heat is also available in Spanish/Espanol.

This page was produced as a cooperative effort of the National Weather Service, the Federal Emergency Management Agency and the American Red Cross.