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A heat wave forecast for much of the US has scientists alarmed

The coming heat is projected to affect huge stretches of the U.S., from eastern New Mexico and Colorado across the Central Plains and into the Northeast.
/ Source: NBC News

A sustained blast of heat is expected to bake much of the United States with hotter-than-usual temperatures this holiday weekend, and forecasts suggest that the heat and the humidity could linger for several weeks.

The extreme weather — the first major heat wave of the season — comes as many states are scrambling to contain the rampant spread of the coronavirus and resources are already strained. And while the pandemic presents some unique challenges this summer, experts say these extreme events will continue to pose public health risks because climate change is making heat waves around the world more frequent and more intense.

The coming heat is projected to affect huge parts of the U.S., from eastern New Mexico and Colorado across the central Plains and into the Northeast.

"The first half of July looks to have well-above-normal temperatures, at pretty high probabilities, beginning around the Fourth of July or slightly before," said Jon Gottschalck, chief of the Operational Prediction Branch at the National Weather Service's Climate Prediction Center.

Some places are already sweltering under record conditions. Miami recently had its hottest week on record and posted its 11th consecutive day with a heat index over 103 degrees, Brian McNoldy, a senior research associate at the University of Miami's Rosenstiel School of Marine and Atmospheric Science, tweeted Thursday.

Gottschalck said it's likely that several regions may be under heat advisories and excessive heat watches, and he said warm conditions may persist into the evenings, with little relief from the humidity.

The heat is being driven by the northward shift of the jet stream, which creates a "ridging effect" — a pocket of high pressure that allows for warm, dry conditions at the surface, Gottschalck said. The impending blast of heat could also create a "ring of fire" weather pattern, in which storms ride along the periphery of the heat dome and trigger severe thunderstorms across the northern Plains, he said.

Current forecasts show that this dome of heat could stick around well into the month.

"Our models indicate that this is going to be somewhat persistent through the first two weeks of July, and potentially longer," Gottschalck said.

He said the Climate Prediction Center has been working closely with the Federal Emergency Management Agency and local agencies on how to manage heat waves and other extreme weather events during the pandemic.

Some cities, for instance, may not be able to provide relief for vulnerable people because of social distancing guidelines.

"We're dealing with such a unique situation, where even if some areas can open up cooling centers and things like that, they're likely to have limited capacity," said Julie Caron, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado. "So now, you could have a vulnerable population that has to make a choice to either stay home and risk the heat or go to a cooling center and risk exposure to the virus."

But even without the pandemic, she said, these events are troubling in the context of global warming.

"There's a long-term warming trend, but we're also seeing an increasing rate of change that's notable since 2015," Caron said. "What that means is we're getting hotter and more frequent heat waves on top of each other."

The changes are magnified in the summer, particularly because July is typically when most parts of the contiguous U.S. have their hottest days of the year.

"You're exacerbating heat extremes in an already hot season," Caron said. "That's why it's not just about heat waves, necessarily. It's that we're seeing hotter-than-normal seasons."