The US heat dome is expected to bring a prolonged spell of dangerous heat across much of the country from late June through the Independence Day weekend, affecting nearly 200 million people across more than two dozen states. According to AccuWeather, the expanding heat dome will push daytime temperatures into the 90-100°F (32-38°C) range, with some cities exceeding 100°F (38°C) for several consecutive days. Combined with dew point temperatures in the 70s°F, the heat index will make conditions feel significantly hotter, increasing the risk of heat-related illnesses.

The National Weather Service warns that extreme heat remains the deadliest weather hazard in the United States, causing more fatalities annually than hurricanes, floods, or tornadoes. Meteorologists say the persistent high-pressure system will trap hot air near the surface, resulting in oppressive heat, high humidity, and limited overnight cooling across large parts of the Midwest, Plains, and Eastern United States.

Heat Dome Expands Across Central and Eastern US

The heat dome is forecast to strengthen over the central United States before gradually expanding eastward through the week.

Cities across the Mississippi and Ohio Valleys are expected to experience several consecutive days of temperatures above 90°F. Chicago could record four to five straight days above 90°F, while St. Louis may endure at least eight consecutive days in the 90s, with highs approaching 100°F well above seasonal averages.

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Humidity Will Make Conditions More Dangerous

One of the defining features of the US heat dome will be exceptionally high humidity.

AccuWeather forecasts dew point temperatures well into the 70s°F, creating uncomfortable and potentially dangerous conditions. Dew points above 70°F are considered highly humid and significantly reduce the body’s ability to cool itself through sweating.

As a result, even routine outdoor activities could increase the risk of dehydration, heat exhaustion, and heat stroke, particularly for older adults, young children, outdoor workers, and people with underlying medical conditions.

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Major Cities Face Strong to Severe Heatwaves

According to the AccuWeather HeatWave Counter and Severity Index™, several major cities are expected to experience prolonged periods of dangerous heat.

Forecast highlights include:

• Chicago: Strong heatwave from June 29-July 3
• New York City: Strong heatwave expected July 1-4
• Philadelphia: Strong heatwave from June 30-July 5, with temperatures possibly reaching 100°F
• Raleigh, North Carolina: Severe heatwave from June 30-July 4, with temperatures exceeding 95°F for multiple days
• Washington, D.C.: Highs of 100°F or above possible for up to four consecutive days
• Newark, New Jersey: Likely to experience multiple days at or above 100°F

Meteorologists note that these temperatures are significantly higher than normal early July averages for many of these cities.

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Thunderstorms May Bring Temporary Relief

• While intense heat dominates much of the country, the edges of the heat dome are expected to generate clusters of thunderstorms stretching from the Rocky Mountains across the northern Plains and into the Midwest and Northeast.
• Additional storms are also forecast along the Gulf Coast. These systems may briefly lower afternoon temperatures but could also produce heavy rainfall, gusty winds, and localized flooding.
• By the Independence Day weekend, a shift in the jet stream is expected to push the heat dome westward toward the Plains.
• Cooler air and more frequent thunderstorms should gradually spread into parts of the Northeast.
• Boston could begin experiencing relief before July 4, while Washington, D.C. may not cool down until late on Independence Day or the following weekend.

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