K-State Research and Extension News
June 28, 2012
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Is a Heat Wave Truly Hot?

MANHATTAN, Kan. – When does hot weather become a heat wave?

Some experts believe daily low temperatures should set the threshold.

“They point to several studies that found an increase in heat-related illnesses and deaths when daily low temperatures remained above 75 degrees. That finding held true, regardless of how extreme the high temperatures were,” said Mary Knapp, State of Kansas climatologist, based with K-State Research and Extension.

In comparison, the National Weather Service definition for “heat wave” is vague: “A period of abnormally and uncomfortably hot and unusually humid weather.”

“The NWS can’t be more specific,” Knapp said. “The actual threshold varies from region to region. A heat wave in Boston could be nice weather for Miami.”

What’s not vague, however, is that hot weather can be deadly. It often leads the annual statistics for U.S. weather-related deaths, placing above hurricanes, tornadoes and floods, she said.

Besides, humidity worsens heat’s effects on the human body – a fact reported nationwide as Heat Index (“feels like”) temperatures.

Knapp said other dependable measures are the outlooks, watches and warnings the National Weather Service issues for excessive heat, just as it does for other extreme weather. Those bulletins immediately become top news.

When the NWS has issued a heat advisory or warning, for example, those classifications can specifically mean:

* Consecutive days with a Heat Index of at least 105 F for three or more hours per day.

* Consecutive days with nighttime lows above 80 degrees.

* Any period of time with a Heat Index above 115 F.


K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by: Kathleen Ward
K-State Research & Extension News

Mary Knapp is at 785-532-7019