A historic heat dome has settled over the central and eastern United States, trapping intense surface heat and soaring humidity across more than two-thirds of the contiguous states. More than 200 million Americans are under heat warnings as temperatures and heat indices approach life-threatening levels.
A thermal feedback loop
The blocking high-pressure system has created a lid over the nation, preventing heat from escaping and locking in a multi-day thermal feedback loop. The combination of extreme temperatures and high humidity has pushed heat indices near 115°F in cities from Chicago to Washington, D.C. The National Weather Service has warned that overnight lows offer little relief, increasing the risk of heat-related illness and death.
Deadliest weather hazard
Extreme heat is among the nation's deadliest weather hazards, killing hundreds to thousands of people annually through heat stroke and other heat-related illnesses, especially during prolonged events. Officials have urged residents to limit outdoor activity, check on vulnerable neighbors, and use cooling centers.
When will it break?
Forecasters expect some relief for the mid-Atlantic states by July 6-7, as the heat dome may shift westward, bringing above-average heat back to the Plains and West. However, the pattern suggests above-normal temperatures will persist across much of the country through mid-July, with the potential for additional record-breaking days as the summer progresses.