A widespread, searing heat dome settles over the US this week

By Meteorologist Chris Dolce, CNN

(CNN) — A heat dome will bring dangerously hot and humid conditions to the eastern half of the United States this week in the region’s most widespread heat wave of the summer so far.

The heat dome is building in response to a large shift in the jet stream that’s also bringing a big cooldown to the West. Powerful winds will accompany the cooldown and intensify already dangerous fire weather conditions in Utah, where a large, destructive fire is ongoing, and in neighboring states.

The cooler temperatures in the West the past few days will be coming to an end. Beginning Monday, temperatures will rise across portions of Utah, Colorado, and Arizona, further complicating firefighter’s ability to fight ongoing wildfires.

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Major cities including Chicago, Detroit, St. Louis, Dallas and Nashville could see thermometers climb to their highest level yet this year early this week. Conditions will be made more oppressive by a big surge of humid air spreading out of the South into the Midwest. The sultry weather pattern will then expand eastward to the Northeast by midweek.

The heat index, or what it feels like with humidity factored in, will soar to hazardous levels across this wide area as the heat dome stagnates and traps hot air for days. Millions will see their so-called “feels-like” temperature hit 100 to 110 degrees; some places will peak as high as 115 degrees.

Heat waves worldwide are becoming more harsh and frequent because of human-caused warming from fossil fuel pollution. The record-shattering heat waves in Europe last week and in the western US in March are two recent examples.

This upcoming heat wave won’t rival those when it comes record-breaking extremes in most areas, but it will be scorching for days and no less dangerous.

Major to extreme heat risk ahead

Heat and humidity will intensify in the South this weekend and then expand northward toward the Midwest and Great Lakes this week. Parts of the Northeast will feel increasingly hot and humid by Tuesday or Wednesday, including New York City, Pittsburgh, Pennsylvania, and Washington, DC.

High temperatures in the upper 90s to near 100 degrees will grip a large area of the South, and highs in the low to mid-90s will be commonplace in the Midwest and parts of the Mid-Atlantic and Northeast. A World Cup match at New York New Jersey Stadium on Tuesday at 5 p.m. ET could start out a bit sweltering with a temperature in the upper 80s and a heat index in the lower 90s.

Tens of millions of people are in a Level 3 of 4 “major” or Level 4 of 4 “extreme” heat risk from the Deep South to as far north as parts of Minnesota, Wisconsin and Michigan and as far east as New York and the Mid-Atlantic on one or more day this week, according to the National Weather Service.

Heat this severe can affect anyone without proper cooling or hydration, according to the weather service. Little relief is expected at night, since high humidity will prevent temperatures from cooling much.

Low temperatures next week won’t fall below the lower-to-middle 70s in the Midwest and Great Lakes. Urban areas could struggle to fall much below 80 degrees.

Prolonged exposure to extreme heat can cause illnesses like heat exhaustion, heat cramps, and the most serious type, heat stroke, according to the US Centers for Disease Control and Prevention. Emergency room visits for heat-related illness surge on “major” and “extreme” risk days, according to the National Weather Service.

Heat is also the deadliest type of weather in the US, with a higher annual average death toll than tornadoes, hurricanes and lightning combined, according to weather service statistics.

Exactly how long this week’s heat dome will stick around is still uncertain, but it could begin to shift west toward the Plains over the Fourth of July weekend. Hot and sticky weather will persist in the South, but could ease up a little for the Midwest, Great Lakes and Northeast during the holiday weekend or just after its over.

This first widespread heat wave is happening right as the central and eastern US begin to enter their usual hottest time of year.

Most of these areas see their average warmest day in July, while the Southern Plains and Lower Mississippi Valley usually experience peak heat in August, according to the National Centers for Environmental Information.

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CNN Meteorologist Briana Waxman and CNN’s Kate S. Petersen contributed to this report.