Millions under extreme heat warning for July 4th weekend

This is according to the National Weather Service's HeatRisk outlook.

The agency said on Friday that the dangerous heat will continue through the July 4th weekend, with the most intense conditions expected across the Midwest, Ohio Valley, Mid-South and East Coast.

A strong upper-level ridge – commonly referred to as a heat dome – remains anchored across the central and eastern U.S., fueling temperatures between 95 and 105 degrees. Combined with high humidity, heat index values are expected to reach 100 to 115 degrees across large swaths of the country.

Forecasters said numerous temperature records are expected to be broken on Friday and Saturday, with some locations at risk of consecutive-day, monthly and all-time record highs.

The National Weather Service warned that one of the most dangerous aspects of the heat wave is a lack of overnight relief. Low temperatures are expected to remain in the 70s to near 80 degrees in many areas, allowing little opportunity for people or buildings to cool down.

"These conditions can bring an increased risk for heat-related illness, especially for vulnerable populations and those without adequate cooling,” the agency said in a press release.

Extreme heat warnings and heat advisories will remain in effect across much of the eastern half of the country through Friday and Saturday. An extreme heat warning is issued when dangerous heat is occurring or imminent, while a heat advisory is issued when conditions are expected to be hazardous but less severe.

The National Weather Service noted that prolonged periods of extreme heat are among the deadliest weather hazards, especially on a holiday weekend when many people spend time outside.

"Protect yourself by limiting time outdoors, staying hydrated, and ensuring access to A/C or cooling centers," heat.gov, the website of the National Integrated Heat Health Information System, said. "Never leave children or animals unattended in vehicles!"