Excessive heat warning

An excessive heat warning is a notice issued by the National Weather Service of the United States within 12 hours of the heat index reaching one of two criteria levels. In most areas, a warning will be issued if there is a heat index of at least 105 °F for more than 3 hours per day for 2 consecutive days, or if the heat index is greater than 115 °F for any period of time.

Note that local offices, particularly those where excessive heat is less frequent or in areas with deserts or mountainous terrain, often have their own criteria. High values of the heat index are caused by temperatures being significantly above normal and high humidities, and such high levels can pose a threat to human life through conditions such as heat stroke, heat exhaustion, and other heat-related illnesses.[1]

Danger to athletes

Due to the extreme illnesses that can occur, athletes should limit their physical activity when an excessive-heat warning is issued. According to the National High-School Sports-Related Injury-Surveillance System, High-School RIO, an estimated number of 51,943 excessive-heat illnesses occurred in nine of the high-school sports observed between 2005, 2011, and 2020.

Example

The following is an example of an excessive heat warning issued by the National Weather Service office in Wilmington, Ohio on July 20, 2011 during a severe heat wave.[2]

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE WILMINGTON OH
944 PM EDT WED JUL 20 2011

KYZ099-100-OHZ026-045-046-052>056-062>065-072>074-079>082-088-
211000-
/O.CON.KILN.EH.W.0002.110721T1600Z-110723T0100Z/
/O.CON.KILN.HT.Y.0004.000000T0000Z-110721T1600Z/
MASON-LEWIS-HARDIN-UNION OH-DELAWARE-CHAMPAIGN-CLARK-MADISON-
FRANKLIN OH-LICKING-GREENE-FAYETTE OH-PICKAWAY-FAIRFIELD-CLINTON-
ROSS-HOCKING-BROWN-HIGHLAND-ADAMS-PIKE-SCIOTO-
INCLUDING THE CITIES OF...MAYSVILLE...VANCEBURG...KENTON...
MARYSVILLE...DELAWARE...URBANA...SPRINGFIELD...LONDON...
COLUMBUS...NEWARK...XENIA...WASHINGTON COURT HOUSE...
CIRCLEVILLE...LANCASTER...WILMINGTON...CHILLICOTHE...LOGAN...
GEORGETOWN...HILLSBORO...WEST UNION...PIKETON...PORTSMOUTH
944 PM EDT WED JUL 20 2011

...HEAT ADVISORY REMAINS IN EFFECT UNTIL NOON EDT THURSDAY...
...EXCESSIVE HEAT WARNING REMAINS IN EFFECT FROM NOON THURSDAY TO
9 PM EDT FRIDAY...

* HEAT INDEX VALUES...UP TO 110.

* TIMING...HEAT INDICES BETWEEN 100 AND 105 WILL CONTINUE INTO
  THE EVENING. THE HEAT INDEX WILL RISE TO BETWEEN 105 AND 110
  THURSDAY AFTERNOON AND EVENING AND THEN AGAIN ON FRIDAY.

* IMPACTS...HEAT EXHAUSTION...HEAT STROKE AND OTHER HEAT RELATED
  ILLNESSES WILL BE POSSIBLE...ESPECIALLY IF YOU SPEND A
  SIGNIFICANT AMOUNT OF TIME OUTDOORS...OR ARE INVOLVED IN ANY
  STRENUOUS OUTDOOR ACTIVITY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE EXTRA PRECAUTIONS IF YOU WORK OR SPEND TIME OUTSIDE. WHEN
POSSIBLE... RESCHEDULE STRENUOUS ACTIVITIES TO EARLY MORNING OR
EVENING.  KNOW THE SIGNS AND SYMPTOMS OF HEAT EXHAUSTION AND HEAT
STROKE.  WEAR LIGHT WEIGHT AND LOOSE FITTING CLOTHING WHEN
POSSIBLE AND DRINK PLENTY OF WATER.

TO REDUCE RISK DURING OUTDOOR WORK THE OCCUPATIONAL SAFETY AND
HEALTH ADMINISTRATION RECOMMENDS SCHEDULING FREQUENT REST BREAKS
IN SHADED OR AIR CONDITIONED ENVIRONMENTS. ANYONE OVERCOME BY
HEAT SHOULD BE MOVED TO A COOL AND SHADED LOCATION. HEAT STROKE
IS AN EMERGENCY...CALL 911.

&&

$$

References
  1. National Weather Service. "Excessive Heat Warning". Glossary - National Weather Service. Retrieved 18 May 2011.
  2. National Weather Service. "Excessive Heat Warning". Iowa Environmental Mesonet NWS Product Archive. Retrieved 21 July 2011.
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