New Hampshire is at the tail end of a record-breaking heat wave, with communities across the state seeing their longest strings of sweltering days in recorded history.
Concord saw temperatures at or above 90 degrees starting on July 6. July 16 marked the city’s 11th day in a row of extreme heat — two days more than the previous longest heat wave, which happened in 2002.
Tuesday marked Manchester’s 12th day of extreme heat, also beating out a 2002 record.
“This is part of what scientists have been expecting as Earth's overall atmosphere gets warmer in response to human emissions of greenhouse gasses,” said Mary Stampone, New Hampshire’s state climatologist and a professor at the University of New Hampshire.
From 1980 through 2010, Concord’s average number of 90-degree days per summer was about 12, Stampone said. Halfway through this summer, the city has surpassed that already.
It’s not only the days that have been hot. Nighttime temperatures have stayed warm, too.
“We’ve had a lot of nights that have stayed above 70 Fahrenheit, which is kind of an extreme nighttime temperature for us here,” Stampone said. “Buildings don’t cool off, plants start to struggle.”
Hot nighttime temperatures, which are increasing faster than daytime temperatures as climate change warms up the atmosphere, can also make it more difficult for people to cool off and can decrease sleep quality.
A hotter atmosphere can also evaporate more water from the surface of the earth, increasing humidity, Stampone said. More humidity means humans are less able to cool off by sweating.
“That can make it feel even hotter,” she said. “We've been having days where the measured air temperature is in the mid 90s, but we're seeing heat indices of 100 or more given the combination of the heat and humidity.”
How New Hampshire experiences extreme heat in the future is still being determined, Stampone said, as humans, businesses and governments decide whether or not to cut greenhouse gas emissions. If cuts are made now, temperatures are projected to peak around 2050 and level off later in the century.
“If we don't do that, and follow sort of that worst case scenario line of business-as-usual, we can see probably twice as many days above 90 in the latter half of the century than if we reduce emissions now,” she said.
In the 2021 climate assessment, Stampone and her team projected that the state could see up to about 60 days above 90 degrees in a high emissions scenario.
“The moral of the story is without reduction in greenhouse gas emissions, we're going to be seeing a lot more of these days above 90 than we would if we do reduce our emissions,” she said.
As heat continues this summer, Jerry Combs, a meteorologist at the National Weather Service in Gray, Maine, urged residents to take precautions.
“If you have to go outside, do it early in the morning or in the evening when the heat of the day is over and the sun angle is lower so you can get access to more shade,” he said. “If you do have to work outside in the heat of the day, stay hydrated, take frequent breaks.”
The heat and humidity New Hampshire has experienced in recent days have also contributed to thunderstorms rolling through communities across the state, Combs said.
“You can kind of think of heat and humidity as like energy for these thunderstorms to survive,” he said.
Last week, storms caused major flooding across northern New Hampshire. On Tuesday, the western part of the state saw trees toppling power lines and damaging houses and cars.
“We saw a very rapid change in conditions, including heavy winds, heavy rains and cloud-to-ground lightning,” said Gregory Seymour, Keene’s deputy fire chief. “We experienced a rapid influx of calls through 911.”
Between eight and 10 homes were so damaged by the storm that residents evacuated for the night, and two people were injured. An additional 15 or 20 homes sustained less significant damage, Seymour said. On Wednesday afternoon, utilities reported about 900 customers were still without power.
More thunderstorms are in the forecast Wednesday, with a severe thunderstorm watch in effect until 8 pm for the southern part of the state. Seymour said that makes it especially important that people keep safety in mind.
“Keep good distance away from downed trees and wires,” he said. “Give crews plenty of room to work.”
People should also keep generators a safe distance from their home.
After another day of sweltering temperatures, relief is on the way. The National Weather Service says Thursday and Friday won’t be quite as hot, and cooler nights are ahead.
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