NOAA’s Watch, Warning & Advisory Products for Extreme Heat

Each US National Weather Service (NWS) Weather Forecast Office (WFO) can issue the following heat-related products as conditions warrant plus they publish information on the Heat Index:

Heat Index forecast map for the contiguous United States

Heat Index forecast map for the contiguous United States

Excessive Heat Outlooks: 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. See the mean heat index and probability forecasts maps.

Much of the USA is in the fifth heat wave of the 2011 season and people are experiencing excess heat and humidity extremes that threaten the lives of vulnerable adults and children. What do the terms , “Heat Wave”, “Heat Index”, “Heat Stress” and “Heat Stroke” mean?

Excessive Heat Watches: (www.nws.noaa.gov/glossary/index.php?word=Excessive+Heat+Watch) are 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/Advisories (www.nws.noaa.gov/glossary/index.php?word=excessive+heat+warning) 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 occurring.

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.

Heat Index temperature - humidity chart

Chart: Courtesy USA National Weather Service of NOAA

To find the Heat Index, look at the Heat Index Table shown here, courtesy of the USA’s National Weather Service.

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.

(That isn’t explicitly shown here, but there is a more technical term used by the Military, Industrial Hygienists,  OSHA and others to include the role that solar radiation contributes, called the WBGT Index – see below)

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.

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 Thermometer reads 110 degreescoolest 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.

For much more information visit the USA National Weather Service’s web page at: www.weather.gov/om/heat/index.shtml

Ed Note: We can’t leave this page without referencing another Heat Index Factor that has been mentioned on this site several times in the past. Just do a site search for “WBGT”  (Wet Bulb Globe Temperature) and you’ll find several articles over time.

In the very first  article in 2004, “Heat Can Kill” ,we said:

A convenient handheld WBGT meter tells you thermal conditions around you and “protects” you from heat stroke while you are in sporting or working activities.

The WBGT index is specified by International Standard, ISO-7243, which defines the following formula based on Ta (natural dry-bulb Temperature), Tnw (natural wet-bulb temperature ) and Tg (Global Temperature):
Outdoor under sunlight: WBGT = 0.7Tnw+0.2Tg+0.1Ta
Indoor without sunlight: WBGT = 0.7Tnw+0.3Tg

Recent searches have turned up a supplier of hand-held WBGT Heat Index monitors at InspectUSA.com


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