More than 100 million people across the United States face dangerous conditions this weekend as a heat dome moves eastward, bringing scorching temperatures and high humidity. Heat advisories are in effect along the north-eastern coast from Portland, Maine, to Wilmington, North Carolina, with daytime heat index temperatures 10 to 15°F above average in some areas.
The National Weather Service warns that overnight temperatures will remain very warm and oppressively muggy. While thunderstorms may break the heat in the north-east by Friday night, heat and humidity will continue to build further south, with the most persistent conditions expected across the south-east and Tennessee Valley this weekend.
In New York City, the heat index is forecast to reach 106°F on Friday afternoon, higher than Phoenix, Arizona. In the south-east, the heat index could exceed 115°F, posing serious health risks to those without access to cooling or adequate hydration. The NWS warns of a long-duration heat wave with little overnight relief and high humidity, increasing the danger of heat exhaustion, illness, and death.
Children, older people, and those with existing health conditions are most at risk, along with outdoor workers, homeless individuals, and those with substance use issues. A heat dome occurs when hot air is trapped by a stalled high-pressure system, causing intense ground heating due to minimal cloud cover. Climate scientists note that heat domes are becoming hotter due to global heating from fossil fuel burning.
In the corn belt, a phenomenon known as 'corn sweat' can increase the heat index by up to 10°F, as moisture is released from maize leaves. Meteorologists also forecast flash flooding from north-east Kansas to much of Indiana, and scattered thunderstorms across parts of New England, the mid-Atlantic, and North Dakota. Dry, windy conditions have triggered red flag wildfire warnings for parts of Utah and Oregon.
