National Weather Service United States Department of Commerce

Massive Heat Wave; Severe Storms and Heavy Rain

A massive heat wave is consuming much of the Midwest into the Southern tier of the U.S. with hazy, hot and humid conditions. These dangerous conditions will likely persist through Thursday as widespread excessive heat warnings and heat advisories are in effect. North and east of the heat and area of high pressure, thunderstorms with damaging and severe winds, large hail and heavy rain are likely. Read More >

A Discussion on Water Vapor (Moisture)


If the air temperature was 90 F with a relative humidity of 60 percent in the afternoon, would it feel more uncomfortable to a person than if it was 75 outside with a relative humidity of 100 percent in the morning?


At 90 with a relative humidity of 60 percent, it would "feel" like 100 degrees outside; at 75 with a relative humidity of 100 percent, it would only "feel" like 80. Despite the much different relative humidity value, the absolute humidity or dewpoint would be about the SAME in both these cases (i.e., dewpoint of 75 degrees). This "feeling" that combines air temperature and moisture in the air is referred to as the "heat index." Please return to the text for further information.

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