An excessive heat watch is a notice issued by the

National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...

of the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

when the

heat index The heat index (HI) is an index that combines air temperature and relative humidity, in shaded areas, to posit a human-perceived equivalent temperature, as how hot it would feel if the humidity were some other value in the shade. The result is als ...

is expected to be greater than 105 °F (41 °C) across the northern states or 110 °F (43 °C) across the southern states during the day, and/or nighttime low

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

will be at least 75 °F (24 °C) or higher for two consecutive days. Note that even with the usual northern/southern criteria, local offices, particularly those with deserts or mountainous terrain, often have their own criteria. High values of the heat index are caused by

temperatures Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

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 stroke or heatstroke, also known as sun stroke, is a severe heat illness that results in a body temperature greater than , along with red skin, headache, dizziness, and confusion. Sweating is generally present in exertional heatstroke, ...

Example

The following is an example of an excessive heat watch issued by the National Weather Service office in

Memphis, Tennessee Memphis is a city in the U.S. state of Tennessee. It is the seat of Shelby County in the southwest part of the state; it is situated along the Mississippi River. With a population of 633,104 at the 2020 U.S. census, Memphis is the second-mos ...

888
WWUS74 KMEG 291957
NPWMEG

URGENT - WEATHER MESSAGE
National Weather Service Memphis TN
257 PM CDT Thu Jun 29 2023

ARZ009-018-026>028-035-036-048-049-058-MOZ113-115-MSZ001>017-
020>024-TNZ001>004-019>022-048>055-088>092-300900-
/O.NEW.KMEG.EH.A.0002.230701T0100Z-230702T0100Z/
/O.CON.KMEG.EH.W.0001.000000T0000Z-230701T0100Z/
Clay-Greene-Craighead-Poinsett-Mississippi-Cross-Crittenden-
St. Francis-Lee AR-Phillips-Dunklin-Pemiscot-DeSoto-Marshall-
Benton MS-Tippah-Alcorn-Tishomingo-Tunica-Tate-Prentiss-Coahoma-
Quitman-Panola-Lafayette-Union-Pontotoc-Lee MS-Itawamba-
Tallahatchie-Yalobusha-Calhoun-Chickasaw-Monroe-Lake-Obion-
Weakley-Henry-Dyer-Gibson-Carroll-Benton TN-Lauderdale-Tipton-
Haywood-Crockett-Madison-Chester-Henderson-Decatur-Shelby-Fayette-
Hardeman-McNairy-Hardin-
Including the cities of Piggott, Corning, Paragould, Jonesboro,
Harrisburg, Blytheville, Wynne, West Memphis, Forrest City,
Marianna, Helena, West Helena, Kennett, Caruthersville,
Southaven, Olive Branch, Holly Springs, Ashland, Ripley MS,
Corinth, Iuka, Tunica, Senatobia, Booneville, Clarksdale, Marks,
Batesville, Oxford, New Albany, Pontotoc, Tupelo, Fulton,
Charleston, Water Valley, Coffeeville, Bruce, Calhoun City,
Houston, Okolona, Amory, Aberdeen, Tiptonville, Union City,
Martin, Dresden, Paris, Dyersburg, Humboldt, Milan, Huntingdon,
Camden, Ripley TN, Covington, Brownsville, Alamo, Jackson,
Henderson, Lexington, Parsons, Decaturville, Bartlett,
Germantown, Collierville, Memphis, Millington, Somerville,
Oakland, Bolivar, Selmer, and Savannah
257 PM CDT Thu Jun 29 2023

...EXCESSIVE HEAT WARNING REMAINS IN EFFECT UNTIL 8 PM CDT
FRIDAY...
...EXCESSIVE HEAT WATCH IN EFFECT FROM FRIDAY EVENING THROUGH
SATURDAY EVENING...

* WHAT...For the Excessive Heat Warning, dangerously hot
  conditions with heat index values up to 115. For the Excessive
  Heat Watch, dangerously hot conditions with heat index values
  up to 113 possible.

* WHERE...Portions of East Arkansas, North Mississippi,
  Southeast Missouri and West Tennessee.

* WHEN...For the Excessive Heat Warning, until 8 PM CDT Friday.
  For the Excessive Heat Watch, from Friday evening through
  Saturday evening.

* IMPACTS...Extreme heat and humidity will significantly
  increase the potential for heat related illnesses,
  particularly for those working or participating in outdoor
  activities.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Drink plenty of fluids, stay in an air-conditioned room, stay out
of the sun, and check up on relatives and neighbors. Young
children and pets should never be left unattended in vehicles
under any circumstances.

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 lightweight and loose fitting clothing when
possible. 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 9 1 1.

&&

$$

References

External links

National Weather Service
{{SevWea nav Weather warnings and advisories

Example

See also

References

External links