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

The heat dome will build 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.

Major cities including Chicago, Detroit, St. Louis, Dallas and Nashville could see thermometers climb to their highest level yet this year by early next 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 this past week and in the western US in March are two recent examples.