Heat dome forecast to scorch East next week

A major heat wave will expand across the Midwest and much of the East during Fourth of July week, with blistering hot temperatures and oppressive humidity posing a danger for millions from the Plains to the East Coast.

Triple digit heat indices are likely for many, and daily low temperatures will remain very warm, offering little relief in the night.

This will be a big change for some that have recently been cooler than usual for June, particularly in parts of the Plains and Midwest.

Heat will build this weekend for parts of the country, and spread east through the week. At least 230 million people in the U.S. — about two-thirds of the U.S. population — could be exposed to extreme heat that could lead to health issues.

(MAPS: 10-Day US forecast highs, lows)

Midwest highlights

The heat will intensify in the Plains and spread into the Midwest this weekend, then lock in place in the Great Lakes and Ohio Valley much of next week.

By Monday, highs in the 90s will stretch as far north as northern Michigan and northern Wisconsin, and 90s will be common in the Midwest through much of next week.

When you factor in the heat index, many across the Midwest will feel like the triple digits, making conditions outright dangerous to be exposed to for long periods. This includes places like Milwaukee, Chicago, St. Louis and Minneapolis. 

A few daily record highs are possible by the middle of the week, especially in the Ohio Valley, where some mid-upper 90s highs are possible.

East

In the East, the hotter air will begin arriving on Monday, and for many will last much of the week.

Highs in the mid-upper 90s will be common and some triple digit highs are possible in the mid-Atlantic for several days in a row. Dangerous heat indices from 100 to 110 degrees are also expected in areas such as Washington, D.C., Philadelphia and Richmond, Virginia.

Some daily record highs are possible along and west of the I-95 corridor from the Washington, D.C. metro into parts of the Virginias and eastern Great Lakes.

And overnight lows may struggle to drop much below 80 degrees in the heart of Philly, Baltimore and Washington, D.C.

Parts of New England and upstate New York may be hot, at times, but may escape the worst of this long-lasting heat next week.

(MORE: Danger of nighttime heat)

South

While the South is used to hot summers, the heat moving in will be both persistent and oppressive.

By this weekend, much of the region will have highs in the 90s, and that torrid heat will linger through all of next week. Some locations could even top 100 degrees, both in the Southern Plains, but also in the Southeast from Virginia into the Carolinas.

Add in the southern humidity, and heat indices will be well over 100 from Texas to the Carolinas. 

A few daily high temperature records could fall in the South through this heat wave, including parts of Florida, North Carolina and Texas.

How long will the heat last?

Will this heat wave cook your Fourth of July weekend?

There's still some uncertainty this far out, as often the case with longer-range forecasts.

The latest computer models suggest the heat dome responsible for this heat wave could retreat westward into the High Plains by the holiday weekend.

If that happens, at least some relief could arrive in the East, especially New England, by the holiday weekend.

Some of our models are also forecasting heat relief in parts of the Midwest and possibly the South the week after the Fourth holiday weekend.

Make sure you check back, as we will continue to update the forecast and keep a close eye on the holiday weekend. 

(MORE: 5 things to know to stay safe in a heat wave)