A persistent upper-level ridge that developed into a heat dome over the Midwest, Plains, and Northeast regions of the United States, beginning on June 20, has led to widespread extreme temperatures and high humidity. The hottest days are expected through June 24.
As of early Monday, June 23, the extreme heat warnings were in effect across parts of Connecticut, Delaware, Illinois, Indiana, Maryland, Massachusetts, Michigan, Missouri, New Hampshire, New Jersey, New York, North Carolina, Ohio, Rhode Island, Vermont, Virginia and West Virginia, among other states.
Many cities have activated emergency response measures. In New York and Boston, cooling centers across the city have been made functional and accessible. The states of Connecticut and Philadelphia have issued public advisories to limit outdoor activity, ensure hydration, and check on vulnerable individuals.
Unseasonable heat pushed temperatures to record levels across parts of the central U.S. over the weekend. Denver matched its all-time high for the day with a temperature of 37.2°C (99°F) on Friday, June 22, whereas Pueblo, Colorado, reached 39.4°C (103°F).
By Saturday, Minneapolis was hitting 35.6°C (96°F), which broke a record high that had stood for over 100 years. St. Paul also experienced unusually high temperatures, which resulted in tying its previous record at 35°C (95°F). In South Dakota, Mitchell reached 40°C (104°F), surpassing its 1988 record of 38.3°C (101°F).
Forecasts show temperatures reaching 37.8°C (100°F) on Tuesday in New York City, Washington, Philadelphia, and Hartford, Connecticut. New York City and Philadelphia haven’t seen such temperatures since 2012. New York City has reached 37.8°C (100°F) in June only three times in its recorded history, and the last time was on June 27, 1966.
The heat wave is made worse by high humidity, especially across the mid-Mississippi and Ohio Valleys, and stretching into the Great Lakes, mid-Atlantic, and Northeast. In several cities across the Midwest and Northeast, the heat index is expected to reach the triple digits early this week.
The humidity will also keep overnight mercury readings uncomfortably high.
The heat dome is forecast to weaken by June 25 and 26, but it may still feel hotter and more humid than usual into early July. Above-average temperatures and humidity are forecast to last beyond June 25 in eastern and southeastern regions.
