Weather.com says a major heat wave is sending oppressive humidity and triple-digit heat indices across the Midwest and East through the Fourth of July weekend. Over 165 million Americans face major or extreme heat-related health issues, with the hardest-hit stretch running from Washington, D.C. to the Carolinas through Sunday.
The National Weather Service’s experimental HeatRisk product puts that number in context by flagging where heat is likely to create major or extreme health problems. In practice, that means the combination of high temperatures, humidity and warm overnight lows is keeping dangerous conditions in place instead of allowing a normal nighttime cooldown.
Washington, D.C. to the Carolinas
Heat indices could top 100 degrees from Washington, D.C. to the Carolinas through Sunday of the Fourth of July weekend, while highs stay in the 90s across much of the southern region. The National Weather Service also says an extreme heat warning means dangerous heat is happening now or is imminent, while heat advisories cover heat that is less unusual but can still be dangerous.
The forecast is worse at night in some places. Daily low temperatures in parts of the mid-Atlantic and Northeast have stayed in the mid-80s, and that kind of overnight heat leaves little relief before the next day’s heat builds again.
On Tuesday, La Crosse, Wisconsin, fell only to 81 degrees, tying four other dates for the city’s all-time warmest low dating to 1872. Rockford, Illinois set a record warm low of 77 degrees, while Louisville, Kentucky and Topeka, Kansas each set record warm lows of 79 degrees.
Ohio Valley and South
Heat alerts had dropped for the Ohio Valley and South even as alerts remained in place for the East Coast and pockets of the Southeast. That split left some areas easing slightly while others stayed under dangerous heat, and the higher risk held through the holiday weekend for Americans in the Midwest and East.
Dallas saw its low drop to 81 degrees on Monday, tying the previous daily record set two years earlier. Daily record warm lows also fell in South Bend, Indiana, Holland, Michigan, Jackson, Kentucky, Dubuque, Iowa and Battle Creek, Michigan.
The heat dome may shift westward by Monday or Tuesday, which could bring a little more relief to the mid-Atlantic and push the strongest above-average heat back toward parts of the Plains and West. Until that change arrives, the immediate concern remains the same: long stretches of heat with little overnight recovery and widespread health risk across the holiday weekend.
Plains and West
That westward shift would not end the event so much as move it. Readers in the Plains and West should watch for the same pattern of high humidity, hot afternoons and warm lows that has already settled over the East, because the forecast points to the heat dome traveling rather than disappearing.
