A significant heat dome is forecast to descend upon at least 17 U.S. states this weekend, bringing extreme heat and humidity to millions, with "feels like" temperatures potentially reaching 115°F.
The high-pressure system, which meteorologists describe as a lid trapping hot air near the surface, is expected to settle over the northern Plains and parts of the Upper Midwest starting Sunday. Widespread actual temperatures are predicted to range from 95°F to 105°F, with the heat index pushing the perceived temperature much higher.
Cities including Omaha, St. Louis, Kansas City, Minneapolis, Des Moines, and Denver are anticipated to experience the most intense conditions. Chicago may see daily highs near 90°F, with some relief possible near the lakefront. The heat is expected to expand eastward around July 14, though it may only linger for a day or two in those regions before the dome potentially re-strengthens over the Plains and persists through the end of July.
This incoming heatwave follows another high-pressure system that affected a large portion of the country last week, where some East Coast cities reported "feels like" temperatures as high as 118°F.
A heat dome forms when a ridge in the jet stream creates a barrier, blocking normal weather patterns and allowing warm air to accumulate and intensify under the high pressure.
Meteorologist Jeff Berardelli noted on X that this heat dome is extreme in its size, duration, and intensity. He indicated that actual temperatures in states like Montana, Wyoming, North Dakota, and South Dakota could reach 110°F. The peak of this initial heatwave is expected from Sunday through Wednesday.
By Saturday, highs in the upper 90s°F and low 100s°F are predicted from the Rockies eastward into parts of California and Oregon, though coastal communities may experience milder conditions. Temperatures are projected to climb further on Sunday, with highs near 105°F expected in parts of Utah, Montana, Wyoming, and the Dakotas. Cities like Billings, Montana; Salt Lake City; and Grand Junction, Colorado, are forecast to approach or challenge all-time record temperatures.
AccuWeather warns that prolonged exposure to high heat index values can lead to serious heat-related illnesses. The slow evaporation of sweat in humid conditions impairs the body's ability to cool itself, making the air feel hotter than the actual temperature.
Vulnerable populations, including the elderly, young children, individuals with chronic health conditions, and those without access to air conditioning, are at the highest risk. Symptoms of heat exhaustion can include heavy sweating, fatigue, nausea, and dizziness. Heat stroke, a more severe and potentially deadly condition that can develop rapidly, may present with symptoms such as headache, confusion, high fever, and nausea.
Organizers of outdoor events are advised to implement cooling stations and ensure access to drinking water. Young children, older adults, and those with pre-existing medical conditions are particularly susceptible to the dangers of extreme heat.