Heat Alerts, How Hot?, Humid, Too, Timing Who Gets Relief, What You Should Do, Why So Hot?

A dangerous, widespread heat dome of high pressure will continue to bake much of the central and eastern U.S. Tuesday, setting the stage for highs to hit potentially hit the triple digits along parts of the Interstate 95 corridor from Boston to New York and Washington, D.C. Muggy conditions will make the heat index surge well beyond that threshold in many areas.

June and even all-time record heat has been observed the past few days in the Midwest and East. Plattsburgh, New York, hit 101 degrees Monday, tying its all-time record high for any day of the year. Go to this link for a rundown of some of the most significant records that have been set.

Here are the main takeaways from the forecast:

Heat Alerts

- The National Weather Service has issued extreme heat warnings and heat advisories from the Eastern Seaboard westward to the lower and mid-Mississippi valleys, as you can see in the map below.

- The highest level heat alerts are now called "extreme heat" warnings. You can find more about those changes here. These alerts indicate that heat illnesses are expected to spike when they are in effect and include Boston, New York City, Philadelphia, Washington, D.C. and Raleigh, North Carolina.

How Hot?

- Dozens of locations, especially in the Northeast, will be within striking distance of daily record highs on Tuesday. Some locations in the Northeast could approach records for any June day, either for forecast highs or low temperatures.

- Boston, New York City, Philadelphia and Washington, D.C. could all flirt with the century mark Tuesday. Boston's all-time June record is 100 degrees, so that could be equaled or surpassed. Philadelphia and Washington, D.C. could have a repeat of flirting with 100 degrees on Wednesday.

- New York's Central Park hasn't reached 100 degrees since July 18, 2012, according to the National Weather Service. Philadelphia hasn't reached 100 degrees in June since 1994. Boston's last 100-degree high was on July 24, 2022.

Humid, Too

- Oppressive humidity is accompanying the heat wave as dew points rise well into the 70s.

- That means the heat index, or feels-like temperature, will be well into the triple digits from the East Coast into the South and parts of the Ohio and mid-Mississippi valleys through midweek.

- This also means that overnight temperatures will not cool off or provide any relief from the daily heat.

Timing Who Gets Relief

- Northeast: Extreme heat through Tuesday, lingering into Wednesday for some. Relief will gradually arrive in New England and New York by Thursday.

-Mid-Atlantic and Appalachians: The worst of the heat will last through Wednesday or Thursday, with some relief dropping temperatures a bit late this week into the weekend, although it will still feel plenty like summer.

- Mid-Mississippi and Ohio Valleys: It will remain uncomfortably hot and humid much of the week.

What You Should Do

- 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.

Why So Hot?

- 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 most efficiently.

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

- This heat dome will only slowly weaken and "flatten out" in the East in the week ahead.

heat dome heat wave forecast northeast midwest

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.