Heat wave to cover huge swath of US in coming days, bringing high temperatures to millions

·2 min read

Most of the nation can expect above-average temperatures in coming days as a giant heat wave is expected to spread across much of the continental U.S. beginning next week.

The heat wave will bring temperatures at least 5 to 10 degrees higher than average to much of the country, according to estimates by the National Oceanic and Atmospheric Administration, which predicts a high probability of above-average temperatures for most of the U.S. over the next several days.

Add in climbing humidity, and many people will experience temperatures that will feel well over 100, according Capitol Weather Gang meteorologist Matthew Cappucci. The heat is a sign of a coming "heat dome," he said.

Temperatures in the mid-100s are forecast for eastern Montana, the Upper Missouri Valley and South Dakota in the first half of the week. Heat indexes could be over 110 in urban areas such as St. Louis, with a slight cool-down possible by the end of the week in some areas. Later in the week, areas of Oregon, Idaho and Washington probably will see temperatures into the 100s.

A heat dome is the result of a strong change in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter, according to the National Ocean Service. The warm air coming from the west part of the Pacific Ocean gets trapped in the jet stream as it approaches land. When that hot air arrives over land, the atmosphere traps it. Winds can move the heat dome around.

Extreme weather conditions such as prolonged heat domes are most often the result of random, short-term and natural weather patterns heightened by long-term, human-caused climate change.

What is a heat dome?: Heat dome brings record-breaking high temperatures to the West, exacerbating drought and wildfires

The latest heat wave comes after the Pacific Northwest heat wave in late June, which caused record-breaking temperatures and hundreds of deaths in Oregon, Washington and British Columbia, Canada.

The Western U.S. has already been experiencing a punishing summer that has shattered hundreds of temperature records, with drought encompassing more than 95% of the region, according to the U.S. Drought Monitor.

'Megafire' status: California's Dixie Fire explodes as western wildfires continue to rage

Meanwhile, about 80 large wildfires are burning across the country, with 19 of them in Montana and the nation's largest, the Bootleg Fire, in Oregon. The hot, dry air underneath a heat dome can help spread wildfires.

Areas in the New England region were expected to be an outlier in seeing cooler temperatures over the next several days, according to NOAA predictions, while the Midwest and Northwest were forecast to see the brunt of the heat.

Contributing: Doyle Rice, Janet Loehrke

This article originally appeared on USA TODAY: Heat wave to bring high temperatures across US starting next week

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