Heat dome brings near historic temperatures to much of eastern US

An intense and nearly historic weather pattern is cooking much of America under a dangerous heat dome this week with triple-digit temperatures in places that haven’t been so hot in more than a decade.

The heat wave is especially threatening because it’s hitting cities like Boston, New York and Philadelphia early in the summer when people haven’t gotten their bodies adapted to the broiling conditions, several meteorologists said. The dome of high pressure that’s parking over the eastern United States is trapping hot air from the Southwest that already made an uncomfortable stop in the Midwest.

A heat dome occurs when high pressure in the upper atmosphere traps heat and humidity, raising temperatues in the lower atmosphere. A heat wave is the persistence of heat, usually three days or more.

A key measurement of the strength of the high pressure broke a record Monday and was the third-highest reading for any date, making for a “near historic” heat wave, said private meteorologist Ryan Maue, a former National Oceanic and Atmospheric Administration chief scientist. The worst of the heat was likely to peak for Northeastern cities on Tuesday, forecasters said.

The National Weather Service says 33 million people, almost 10% of the country, will feel blistering 100-degree heat on Tuesday.

New York hasn’t seen 100 degrees since 2011 and Philadelphia, which is forecast to have consecutive triple-digit days, hasn’t reached that mark since 2012.

Humidity is the multiplier in the heat dome equation. The area of high pressure will allow for a lot of evaporation to occur from the wet grounds locally and regionally, which will increase the heat indices quite a bit.



Thousands of Chicagoans flocked to Lake Michigan beaches to beat the heat on Monday. (AP Photo Kiichiro Sato)