CHICAGO—A broad heat wave spread across much of North America on Friday, placing parts of 23 U.S. states under heat-related warnings and advisories as forecasters warned of prolonged periods of dangerous temperatures and high humidity across large sections of the country.
The U.S. National Weather Service (NWS) issued a range of heat alerts covering portions of the Midwest, Great Lakes, Ohio and Tennessee valleys, the Mid-Atlantic, Southeast and parts of the Plains, with meteorologists warning that the combination of high temperatures and humidity could significantly increase the risk of heat-related illness. Forecasts also indicated expanding heat across the western United States under a persistent upper-level ridge.
The Weather Prediction Center said anomalously hot conditions were expected to continue across broad areas of the country, with daytime highs reaching the 90s and above 100 degrees Fahrenheit (38 degrees Celsius) in some locations. Overnight temperatures were also forecast to remain unusually warm in many areas, reducing opportunities for relief and increasing health risks for vulnerable populations.
The National Weather Service urged residents to limit strenuous outdoor activity during the hottest parts of the day, stay hydrated, use air-conditioned spaces when available, and check on older adults, young children and others who are especially susceptible to heat stress. Local officials in several affected areas opened cooling centers and advised employers and event organizers to take additional precautions where extreme heat was expected.
Forecasters said the expansive heat was being driven by a strong dome of high pressure that trapped hot air over much of the continent. The pattern was expected to persist into the weekend across many regions before gradually shifting, although temperatures were forecast to remain above seasonal averages in several states.
The Climate Prediction Center also highlighted continued risks of extreme heat beyond the immediate forecast period, particularly across the southern Plains and lower Mississippi Valley, while noting additional hazards including heavy rainfall in parts of the Southeast and monsoon-related precipitation in the interior West.
Meteorologists said the exact number and location of heat warnings and advisories could change as local forecast offices updated conditions. Officials continued to advise residents to monitor the latest forecasts and heed local emergency guidance as the heat wave evolved.
