In the disastrous heat wave of 1980, more than 1,250 people died. In the heat wave of 1995 more than 700 deaths in the Chicago, Illinois area were attributed to this event. And 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 one section or another of the United States. East of the Rockies, they tend to combine both high temperature and high humidity although some of the worst 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: when the potential exists for an excessive heat event in the next 3 to 7 days. An outlook is used to indicate that a heat event may develop. It is intended to provide 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: 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. It is intended to provide enough lead time so those who need to set their plans in motion can do so, such as established individual city excessive heat event mitigation plans.
Excessive Heat Warning/Advisory: 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 occurrence. 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
National Weather Service Heat Index Based Guidance
The "Heat Index" (HI) is sometimes referred to as the "apparent
temperature". The HI, given in degrees F, is a measure of how hot
it really feels when relative humidity (RH) is added to the actual air
temperature.
To find the HI, 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 RH is 65% (found on the left of the table), the HI-or how hot it really feels-is 121°F. This is at the intersection of the 96° column and the 65% row.
IMPORTANT:
Since HI values were devised for shady, light wind conditions, EXPOSURE
TO FULL SUNSHINE CAN INCREASE HI VALUES BY UP TO 15°F. Also, STRONG
WINDS, PARTICULARLY WITH VERY HOT, DRY AIR, CAN BE EXTREMELY HAZARDOUS.
Note on the Heat Index Chart shaded zone above 105°F. This corresponds to a level of HI that may cause increasingly severe heat disorders with continued exposure and/or physical activity.
NOAA's Heat Alert Procedures based mainly on Heat Index Values
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 two consecutive days. The procedures are:
· Include Heat Index values in zone and city forecasts.
· Issue Special Weather Statements and/or Public Information Statements
presenting a detailed discussion of: Extent of the hazard
including Heat Index values, who is most at risk, and safety rules for reducing
the risk.
· Assist state/local health officials in preparing Civil Emergency
Messages in severe heat waves. Meteorological information
from Special Weather Statements will be included as well as more detailed medical
information, advice, and names and telephone numbers of health
officials.
· Release all of the above information to the media and over NOAA
All-Hazard Weather Radio
Heat Health Watch/Warning System
Recent research has shown that a heat index threshold does not fully account for a variety of factors which impact health including the impact of consecutive stressful days on human health, the time of year, or the location where excessive heat events occur. For example, studies indicate large urban areas are particularly sensitive to heat early in the summer season. Based on this research, NOAA/NWS has supported the implementation of new Heat Health Watch/Warning System (HHWS) that its forecasters use as guidance in producing their daily warning and forecast products. This system was developed in conjunction with researchers at the University of Delaware.
As of summer 2007, about 20 Weather Forecast Offices (WFOs) now utilize the HHWS as additional guidance in their forecast decision-making process. The NWS goal is to expand the HHWS coverage to include approximately 70 vulnerable urban cities across the continental U.S. with mostly populations of 500,000 or more.
The HHWS, tailored for each urban locale, is the first and only meteorological tool based upon the occurrence of certain air masses that have historically been associated with elevated mortality levels. Air masses consider the entire "umbrella" of air over a region, rather than a single meteorological variable such as the heat index. HHWS consider numerous meteorological, seasonal, and social factors, and are based upon actual human health responses. Through the use of, it is possible to predict the likelihood of excess mortality given the synoptic conditions present at specific cities, the number of consecutive days an oppressive air mass is present, and the time of year the event occurs.
Currently, those urban areas with HHWS coverage include Philadelphia, PA; Seattle, WA; Dallas, Fort Worth and Houston. TX; Phoenix and Yuma, AZ; Baltimore, MD; Washington, D.C.; Chicago, IL; St. Louis, MO Cincinnati and Dayton, Ohio; New Orleans, Baton Rouge, Lake Charles, Alexandria, Shreveport and Monroe, LA.; Memphis, TN; Jackson, Meridian and Tupelo, MS; Little Rock and Pine Bluff, AR; Portland, OR; Minneapolis, MN; San Francisco and San Jose, CA.
The NWS forecaster analyzes the HHWS guidance, as well as heat index values, time of year and expected length of the heat event, collaborate with neighboring WFOs as needed, and then decide which, if any, excessive heat product to issue. If an Outlook, Watch, Warning, or Advisory will be issued, the forecaster will notify the local health department and/or emergency management agency to insure that they are aware of the excessive heat forecast.
How Heat Affects the Body Human
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.
Too Much 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 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.
Ranging in severity, heat disorders share one common feature: the individual
has overexposed or over exercised for his age and physical condition in
the existing thermal environment.
Sunburn, with its ultraviolet radiation burns, can significantly
retard the skin's ability to shed excess heat. Studies indicate
that, other things being equal, the severity of heat disorders
tend to increase with age-heat cramps in a 17-year-old may be heat
exhaustion in someone 40, and heat stroke in a person over 60.
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.
Cities Pose Special Hazards
The stagnant atmospheric conditions of the heat wave trap pollutants
in urban areas and add the stresses of severe pollution to the already
dangerous stresses of hot weather, creating a health problem of undiscovered
dimensions. A map of heat-related deaths in St. Louis during 1966, for
example, shows a heavier concentration in the crowded alleys and towers
of the inner city, where air quality would also be poor during a heat
wave.
The high inner-city death rates also can be read as poor access to
air-conditioned rooms. While air conditioning may be a luxury in
normal times, it can be a lifesaver during heat wave conditions.
The cost of cool air moves steadily higher, adding what appears to
be a cruel economic side to heat wave fatalities. Indications from
the 1978 Texas heat wave suggest that some elderly people on fixed
incomes, many of them in buildings that could not be ventilated without
air conditioning, found the cost too high, turned off their units,
and ultimately succumbed to the stresses of heat
Excessive Heat Cautions and Safety Tips
Preventing Heat-Related Illness
Elderly persons, small children, chronic invalids, those on certain
medications or drugs (especially tranquilizers and anticholinergics),
and persons with weight and alcohol problems are particularly susceptible
to heat reactions, especially during heat waves in areas where a moderate
climate usually prevails.
Heat Wave Safety Tips
Slow down. Strenuous activities should be reduced, eliminated, or rescheduled
to the coolest time of the day. Individuals at risk should stay in the coolest
available place, not necessarily indoors.
Dress for summer. Lightweight light-colored 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 non-alcohol fluids. 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 drink alcoholic beverages.
Do not take salt tablets unless specified by a physician.
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 environment affords some protection.
Don't get too much sun. Sunburn makes the job of heat dissipation that much more difficult
Know These 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 muscles of legs and abdomen
possible. Heavy sweating. First Aid: Firm pressure on cramping
muscles, or gentle massage to relieve spasm. Give sips of water.
If nausea occurs, discontinue use.
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. Lay down and loosen
clothing. Apply cool, wet cloths. Fan or move victim to air conditioned
room. Sips of water. If nausea occurs, discontinue use. 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. 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 NOAA's National Weather Service (NWS), the Centers for Disease Control and Prevention (CDC), and the U.S. Department of Homeland Security (DHS). This guidebook provides best practices that have been employed to save lives during heat waves in different urban areas, and provides a menu of options that communities can use in developing their own mitigation plans.
Produced as a cooperative effort of NOAA's National Weather Service, the Federal Emergency Management Agency, and the American Red Cross.
