Aug 10, 2021 - Science

Heat wave engulfs much of U.S., as wildfires rage in West

Weather map of the United States showing orange and red colors marking a heat wave in August 2021.

Computer model projection of forecast high temperatures for Wednesday. (WeatherBell)

Heat warnings and advisories are in effect for at least two dozen states through the end of the week. 25 million people are projected to see highs reach or eclipse 100 degrees Fahrenheit this week, as yet another powerful heat dome-dominated weather pattern affects a huge swath of the country.

Why it matters: The heat wave will combine with drought conditions in the Pacific Northwest to aggravate an already dire wildfire situation and bring more miserable weather to residents of Portland, Oregon, and other states hit hard by record-shattering heat in late June and early July.

  • This time around, heat and high humidity will combine to make for dangerously hot conditions in the Mid-Atlantic and Central states, too.
  • The hot and dry weather will only worsen the ongoing wildfires and potentially lead to new ignitions from thunderstorms. California's Dixie Fire, the second-largest blaze in state history and the largest ongoing wildfire in the U.S., grew further overnight toward the 500,000-acre mark, threatening more homes.

By the numbers: A strong area of high pressure across the Pacific Northwest, also known as a "heat dome," will ratchet up the heat from Northern California to Washington state from Wednesday through Saturday in particular.

  • High temperatures of up to 112 degrees are possible in inland valleys in western Oregon, the National Weather Service predicts, with little overnight relief in many areas.
  • High temperatures will generally be from 10 to 15 degrees above average for this time of year.

Threat level: When it comes to fire weather, the Weather Service forecast office in Medford, Oregon, is warning of "excessively hot, very unstable and dry air" across southern Oregon and Northern California — where the Bootleg Fire is still burning, in addition to the Dixie and other blazes.

  • Fire weather warnings for potentially extreme wildfire behavior, including the formation of pyrocumulus clouds, go into effect Wednesday.
  • Portland, Oregon, which set an all-time high temperature record of 116 degrees back in July, is predicted to reach a sizzling 104 degrees Thursday.
  • Meanwhile, in the Eastern U.S., highs in the mid-to-upper 90s will affect the urban corridor between Washington and Boston, with scorching heat even reaching parts of New Hampshire and Maine.

Context: The heat wave comes just a day after a landmark climate science report was released by the UN Intergovernmental Panel on Climate Change (IPCC), which definitively linked the increasing frequency and severity of heat waves to human emissions of greenhouse gases.

  • The report described this connection as "established fact," a striking increase in confidence level since its last major assessment, which is the equivalent of a CT scan for the planet, in 2013.
  • At the same time as the U.S. is feeling the heat and seeing more than 105 large wildfires burn across the country, a brutal heat wave in the Mediterranean region is continuing to fuel deadly blazes in Greece and Turkey.
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