An intense and long-duration heat wave kicks into high gear Friday, with 150 million people set to experience temperatures hotter than 90 degrees over the next week, and 50 million of those forecast to experience temperatures over 100 degrees.
More than 80 million people were under heat alerts on Friday from the Central and Southern Plains as well as for nearly the entire West Coast. The myriad of heat alerts covering the map included heat advisories, excessive heat watches and excessive heat warnings all issued by the National Weather Service.
Dallas, Houston, Phoenix, Las Vegas, Los Angeles, Portland and Seattle are among the cities under heat alerts.
For the Plains, high temperatures were forecast to be 100-107 degrees, and heat index values 105-115 degrees. This heat is forecast to last through Sunday with cooler temperatures expected next week.
For the West, an excessive heat warning is in effect from Friday until Wednesday for parts of Arizona, California and Nevada, with high temperatures expected to reach 110-125 degrees.
Two factors making this heat event especially dangerous is the long duration into next week, and the fact that it will be more humid than usual.
Temperatures in the upper 90s and 100s could persist for the next 10 days. Often times it’s not simply the hot temperature that matters on a single day, but instead how many consecutive days in a row temperatures remain at dangerous levels.
“The longevity of the heat is more concerning than the record-breaking temperatures,” said National Weather Service meteorologist Trevor Boucher.
When talking about the west, the heat is often described as a “dry heat.” This time, however, tropical moisture streaming into the region from what was Hurricane Elida (since dissipated) will make conditions more muggy than usual and thus more dangerous. Humidity makes it harder for the body to cool off, and also keeps nights warmer than usual which is supposed to be the recovery period for bodies to cool down.
When nights stay hot, that amplifies the risk for heat related illnesses during the day.
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“If people are trying to get out of 90-degree temperatures, they’re going to be hard pressed to do it. Even in the shade, you’ll probably be looking at high temperatures well over 100, and these are the kinds of situations that can relate to the stack-up of heat-related calls and visits to the hospital,” Boucher said.
By the time the heat event is over, more than 100 daily record highs could fall between Friday and early next week. Cities forecast to set new records include Dallas, Las Vegas, Phoenix and Sacramento.
The monthly heat records are especially notable. Death Valley, California is forecast to get above 125 degrees Sunday-Tuesday which will be the hottest temperatures on record so late in the season.
If Phoenix reaches 117 that would match the all-time hottest temperature recorded during the month of August.
This heat will be exceptionally dangerous for the more vulnerable populations, especially in cities, where the urban heat island effect — where a city’s temperature is much warmer than rural areas nearby — combined with less access to air conditioning will amplify the risk for heat illness.
Boucher stressed the importance of public cooling stations to help people get out of the heat, as well as people being smart about their home’s energy use, given that people will likely be running their air conditioning throughout the day and night.
“The question we often get is, ‘you know, it’s summer. Why are we worried about it being hot? This is normal.’ Well, this type of heat, this magnitude of heat for this long is not normal,” Boucher said.
Alexander Gershunov, a research meteorologist at Scripps Institution of Oceanography, University of California, San Diego, said heat waves of this nature are becoming more common due to climate change.
“These large and long-lasting heat waves are typically caused by a dome of high pressure building overhead, and this one has a particularly strong high pressure and it’s very extensive in that it pretty much dominates the entire Southwest of the United States,” Gershunov said. “So these patterns happen, and when they occur at the time of the warmest summertime temperatures in late July and early August, they can cause severe heat waves.”
The heat wave stands to exasperate the COVID-19 pandemic — and the pandemic will make matters worse for those facing the heat, too. Indoor cooling centers, for example, could potentially contribute to the coronavirus’ spread if large crowds gather. People who lost their jobs may avoid running their air conditioners out of fear that they won’t be able to afford their energy bill. And heat waves, like the coronavirus, both impact the respiratory system.
“With COVID-19 and other crises layered on top of each other, an additional extreme weather crisis basically just compounds the stress that people are already feeling,” Gershunov said.
Climate change is increasing the frequency, duration, and intensity of heat waves like this, especially out West. Las Vegas is the fastest warming U.S. city, with Phoenix, Tucson and El Paso also near the top of the list.
Phoenix has already broken the record this year for number of days 110 degrees or higher, and if the city reaches 115 degrees Friday that will also set a new record for number of days (8) with a high of 115 or above. Phoenix is currently twice as likely to hit 110+ degrees compared to the 1950s.
And the heat is no doubt exacerbating the fire risk across the West.
Red flag warnings were up on Friday for parts of Wyoming, Oregon and Washington and included Portland.
Very hot temperatures combined with low humidity and wind gusts up to 40 mph made conditions favorable for fire ignition and rapid fire spread.
While there were no red flag warnings up for southern California, the Lake Fire in Los Angeles County continued to burn. As of Friday morning that fire covered 11,000 acres and was 12% contained.
In Colorado, the Pine Gulf Fire north of Grand Junction grew to 73,381 acres making it the fourth largest fire in Colorado History.
The intense heat ramping up across the West comes on the heels of the National Oceanic and Atmospheric Association (NOAA) releasing its July monthly climate report on Thursday stating that July 2020 was the second hottest July on record for the planet, and the #1 hottest on record for the Northern Hemisphere. It also stated that arctic sea ice reached record lows.
Globally, 2020 is shaping up to be one of the hottest years on record.