Dangerous heat wave to bake the U.S. through July Fourth

Heat index values of about 105 to 110 were expected across much of the central United States Wednesday and Thursday, with conditions likely to last into the July Fourth holiday weekend. In some places, warm nighttime lows were expected to offer little overnight relief, keeping the risk high after sunset.

Humidity would make the heat feel worse. NOAA’s Weather Prediction Center projected widespread temperatures in the 90s to low 100s. Cities could feel even hotter because of the urban heat-island effect.

National Weather Service guidance puts Heat Advisory criteria at a heat index of 105 or higher east of the Blue Ridge and 100 or higher west of the Blue Ridge. Advisories are typically posted when dangerous conditions are expected within the next 24 to 36 hours. The agency’s HeatRisk system was already flagging heat in the seven-day forecast across much of the central and eastern contiguous United States.

CDC and National Weather Service data show hot weather causes an average of more than 1,220 deaths a year in the United States when heat is listed as a cause or contributing cause. The CDC also tracks heat-related illness that can include cardiovascular and respiratory complications, renal failure, electrolyte imbalance, kidney stones and adverse fetal outcomes.

National Weather Service data show extreme heat has killed more people in the last 10 years than any other weather phenomenon. NOAA’s Climate Prediction Center projected extreme heat could continue into the week of July 5 to 11 across much of the central and eastern contiguous United States.