Saturday was another very hot day in much of the United States, and weather experts said the nation would experience warmer-than-normal temperatures for the rest of summer and into autumn in the Northern Hemisphere.
The National Weather Service issued an excessive-heat warning for much of the U.S., from North Dakota to the Mid-Atlantic states and into the South. Meteorologists blamed the miserable conditions on a "heat dome" over the country — a stationary or extremely slow-moving high-pressure system in the upper atmosphere that holds a large mass of hot, humid air in place, causing sweltering conditions on the ground below.
The excessive heat zone included Philadelphia, where the Democratic National Convention will open Monday. Officials cautioned anyone planning protests or other demonstrations outside the convention hall to be careful, drink lots of water and avoid camping outdoors near the site.
Medics will be standing by to treat anyone affected by the dangerous weather.
Temperatures as high as 40 degrees C (104 degrees F) were expected in some areas through Monday. High humidity caused by extremely warm water in the Gulf of Mexico will make the weather even more oppressive.
All but one of the 48 continental U.S. states recorded temperatures of 32 degrees C (89 degrees F) or higher on Friday. Washington state on the Pacific Coast was the lone exception to the high heat. (The customary "lower 48 states" designation in weather reports omits Hawaii and Alaska, because they are so distant from the other states.)
Thunderstorms in some areas may provide relief, but only a brief respite from the heat, which is dangerous to people, livestock and crops.