Why Was Maine Sweltering?

Typically, Maine is a summer destination for people who want to cool off.

The state usually boasts average summer temperatures in the upper 70s and low 80s. So why was Maine, along with New Hampshire, Massachusetts, and other parts of New England, in the heat danger zone this week, with skyrocketing temperatures well into the 90s?

Andrew Orrison, a meteorologist with the National Weather Service, said the cause was a kind of weather system that usually forms farther over the Atlantic Ocean and farther south.

The shift of this expansive band of heat toward the coast and farther north helped send temperatures soaring in New England, he said. It was part of a larger “high-pressure aloft” system, a type of phenomena that can produce heat domes.

Additionally, descending westerly winds off the mountain ranges in New England helped to further compress the heat into the lower elevations, which meant higher temperatures in many cities, Mr. Orrison added.

Now that same band of heat has moved further south and is sitting over New York City.

Although high-pressure systems closer to the surface mean fair weather, ones in the atmosphere (the so-called “aloft” systems) can mean days of sustained heat, with little cloud cover to disrupt the power of the sun.

As these high-pressure systems weaken, they can create space for low-pressure events to develop, which is why thunderstorms threatened the area yesterday.

And then there is climate change. The continued burning of greenhouse gases means that the temperature of the atmosphere is increasing almost everywhere, said Jason Smerdon, a professor at the Columbia Climate School.

Though the underlying causes of the most recent heat wave in the Northeast are yet to be determined, he said, the combination of high temperatures and humid conditions created a “double whammy” effect, since a warmer atmosphere holds more moisture.

“So the ‘feels-like’ temperature from combined heat and humidity made the event particularly severe,” he said.