Jul 23, 2021 - Energy & Environment

Next heat dome to build across Lower 48, aggravating drought, fires

Map showing red hues covering the U.S. and parts of Canada as another heat wave hits the region.

Computer model projection for temperature departures from average on July 28, 2021. (WeatherBell.com)

A significant and far-reaching heat wave is poised to build across much of the continental U.S. during the next few weeks, and it could be the most expansive in the country so far during this unusually hot summer, aggravating drought and wildfires.

The big picture: Forests across the West are already burning at a scope and intensity that's unusual for this time of year. Drought data released Thursday showed that what is already the worst Western drought so far this century is only intensifying. Any additional heat will aggravate an already dire situation.

  • The U.S. Drought Monitor shows that 65.4% of the Western U.S. is in "extreme" to "exceptional" drought conditions, the two worst categories on the scale, up from 52.8% on June 1.
  • The only modest relief in sight is for parts of Arizona, New Mexico, Utah and Nevada, where monsoonal moisture will bring rounds of thunderstorms. These storms could also ignite new fires, though, by delivering lightning but little rain in some areas.

Driving the news: A "heat dome," which is an area of high pressure aloft that helps to lock in place hot, dry weather, will form this weekend over the West and eventually migrate to a position across the Central Plains.

  • Computer models show temperatures climbing to 10°F to 15°F or higher above average for this time of year across the affected areas.
  • That may not sound like a major event, but late July is just past what is typically the hottest time of the year, which means temperatures will easily reach the triple digits from portions of the Pacific Northwest to the Plains, parts of the Midwest and Eastern U.S. (with the exception of the Northeast).

What's next: The heat will first build in the Pacific Northwest and Intermountain West on Monday and expand east into Tuesday and Wednesday, when the heat dome will be be broadly centered over Colorado and the adjacent Plains states.

  • Above average temperatures are likely by Thursday from coast-to-coast, with the hottest conditions compared to average occurring in the Plains and Midwest, where some areas could see anomalies of 20°F above average.
  • Cities such as Des Moines, Minneapolis and Chicago will be in the path of the heat wave by the middle of next week.
Map with red and blue colors showing temperature outlook across the U.S. in the next week to two weeks.
Temperature outlook from the Climate Prediction Center for July 28 to August 1. (NOAA)

How it works: While heat waves are a normal feature in the summertime, climate change from human-caused emissions of greenhouse gases is increasing their intensity, duration and frequency.

  • For example, scientists concluded that the Pacific Northwest heat wave, which broke all-time heat records in dozens of locations — including Seattle and Portland at 108°F and 115°F, respectively — was so severe it was "virtually impossible" in the absence of global warming.
  • This event will be the fifth distinct heat wave the U.S. will have seen so far this summer.

Context: Model projections are showing the heat won't fade quickly, but could stick around for much of August as weather patterns pile up like cars on the Washington Beltway, going nowhere fast.

  • Stuck weather patterns featuring strong areas of high pressure aloft have been to blame for several deadly extreme weather events this summer, including the Pacific Northwest heat wave that is thought to have killed hundreds in the U.S. and Canada, as well as the Central Europe floods that have killed at least 200.
  • In much of the West, heat and drought will continue to feed off each other in a vicious cycle, with the hot temperatures drying soils further — allowing more incoming solar radiation to go directly into heating the air.

The intrigue: Environmental groups are hoping the extreme weather events this summer will move the needle on legislation aimed at reducing greenhouse gas emissions and bolstering the resilience of American infrastructure.

  • An event held Thursday by the environmental groups Climate Power and the League of Conservation Voters brought a diverse group of people to Capitol Hill to convey that sense of urgency.
  • Rep. Sean Casten (D-Ill.), who chose WGN-TV chief meteorologist Tom Skilling to speak at the event, told Axios on Thursday that the stories he's hearing from this summer are sobering, and that they underscore the need for the Senate to "do their job."
  • "People are now getting it because it's tangible and they can't say, 'well this is just a crazy scientific theory and prediction but I don't think it's going to happen,'" Casten told Axios.
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