Dangerous Heat Ahead For Midwest, Northeast

An expansive heat wave will spread through the central U.S. as summer officially arrives late this week and then into the East, bringing the hottest temperatures of the year and uncomfortably muggy air to the Midwest and Northeast.

Here are the main takeaways from the forecast:

When Will Heat Arrive?

Here's when we expect the heat to move in:

- Plains: Beginning Thursday

- Mississippi Valley: Beginning Friday

- Rest of Midwest, Northeast: Beginning this weekend

(MAPS: 10-Day Forecast US Highs/Lows)

How Hot?

- In general, we're forecasting highs in the 90s to spread over much of the country east of the Rockies, except for the far northern tier.

- Parts of the Great Lakes and interior Northeast have yet to reach 90 so far this year, according to the Southeast Regional Climate Center.

- A few locations could approach or top 100 degrees during the heat wave, including Denver by Friday, which only happens twice a year on average. New York City and Philadelphia could also flirt with the century mark during the peak of the heat wave next week.

- New York's Central Park hasn't reached 100 degrees since July 18, 2012, according to the National Weather Service.

Humid, Too

- More oppressive humidity will accompany the heat wave late this week into next week.

- This will particularly be the case in the mid-Mississippi and Ohio Valleys, but also into the upper Mississippi Valley, Great Lakes and at least parts of the mid-Atlantic and interior Northeast.

- That means the heat index, or feels-like temperature, will be in the triple digits on one or more days for some cities in the Midwest and Northeast this weekend into early next week.

(MORE: Why The Dew Point Temperature Matters)

How Long Will It Last?

- Plains: Relief should arrive by next Monday

- Mississippi Valley: Relief may arrive in most areas by next Tuesday

- Rest of Midwest: Relief may arrive by next Wednesday

- East: Heat may persist into much of next week

(MORE: Summer Outlook)

What You Should Do

- Heat is the number one weather killer in the U.S., with hundreds of fatalities each year.

- The combination of heat and humidity lingering into the night for several days in a row could be dangerous for those without access to air conditioning, especially in the cores of larger cities.

- Check on family, friends, the elderly and those with chronic illness who live without access to air conditioning.

- If possible, avoid being outdoors for long in the peak heat of the afternoon.

- If not, take frequent breaks, avoid strenuous activity, drink more water than usual and wear loose, lightweight clothing.

(MORE: How To Cool Your Home Without A/C | Heat Advice From An ER Doctor)

Why So Hot?

- This heat wave will be triggered by a change in the jet stream pattern.

- Specifically a strong bubble of high pressure aloft known as a heat dome will develop over the eastern U.S.

- Sinking air near the center of this heat dome suppresses clouds, allowing the intense sunshine this time of year to heat the ground and air above it.

- Southerly and southwesterly winds will also tap hot and humid air from the South into the Midwest and Northeast.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.