Updated Jun 17, 2021 - Energy & Environment

Historic heat wave expands across California, wildfire risk builds

Map showing temperatures in the West, with colors corresponding to extreme heat.

Forecast high temperatures on Thursday from the National Weather Service. (Weatherbell)d

The record-breaking heat wave roasting the West is expanding its grip on Thursday, with the focus of the triple-digit heat shifting into California — particularly the Central Valley and desert regions.

Why it matters: Across the West, the combination of record heat, preexisting drought conditions, and dry lightning strikes from afternoon thunderstorms threatens to ignite numerous wildfires Thursday.

  • Fires have already been burning in Montana, Arizona and other states affected by the heat wave.
  • More than 40 million people across the West and Southwest are likely to see temperatures in their area exceed 100°F during the next several days.

Between the lines: Climate change is making this event more severe than it otherwise would be, based on numerous scientific studies of similar extreme weather events.

  • According to research by climate scientist Michael Wehner of Lawrence Berkeley National Laboratory, human-caused climate change is boosting temperatures by about 3 to 5 degrees during this heat wave.
  • "Increases in extreme heat are one of the most conspicuous aspects of climate change," Wehner told Axios via email. "These increases have already been detected and attributed to fossil fuel consumption using very formal methods."
  • A study published last year found an increase in the occurrence of extreme heat events that overlap with unusually dry conditions, tying this trend to climate change.

Details: The sprawling area of high pressure, known as a heat dome, is drifting west and now has the Golden State in its grip. High temperatures of up to 110°F are forecast for inland portions of Southern California, northward into the Central Valley, and even stretching toward portions of the San Francisco Bay area and northern parts of the state.

  • The operator of the California electric grid has issued a "Flex Alert" for Thursday, asking residents to reduce their electricity use at peak times of day, as it works to balance spikes in power demand with supply.
  • Due to the drought, the state cannot rely on importing as much hydroelectric power as it normally would. This could prompt natural gas plants to be turned on during peak periods.

Threat level: According to the National Weather Service, temperatures across the West will be 10°F to 25°F above average for this time of year. Forecasters are not holding back in their use of language, either: "Dangerous and potentially deadly heat will continue throughout the Southwest and Intermountain West," forecasters wrote in an online discussion.

  • Las Vegas hit 116°F on Wednesday, just 1°F shy of its hottest temperature ever recorded.
  • Tuscon, Ariz. reached 110°F or above for the fifth straight day in June. That streak is expected to reach the longest ever recorded there, at at least 8 days.
  • "Residents enduring the abnormal heat are urged to stay hydrated and avoid extended periods of time outdoors if possible," the Weather Service stated. High temperatures in the Sacramento region could peak at about 113°F.
  • Inland portions of the L.A. and San Diego metro areas will sizzle, while cool breezes off the Pacific keep coastal sections relatively cool.

Of note: The area at greatest risk for wildfires on Thursday is in southern Wyoming, due to the combination of heat, dry soil and high winds.

  • However, California, Nevada and the Four Corners states are also at an elevated risk, particularly due to the likelihood of dry thunderstorms erupting in Northern California. Such storms produce cloud-to-ground lightning, but only light amounts of rain, leading to wildfires.
  • According to the Weather Service, soils are at record dry levels for this time of year in parts of Northern California, for example. In parts of the West, soils haven't been this dry so early in the year since modern records began 120 years ago.

The big picture: The West is enduring its most extensive and severe heat wave since the start of this century, and the heat wave and drought are intensifying one another. Given the record levels of soil dryness, more solar radiation goes into heating the air, rather than evaporating moisture in soils.

  • This pushes air temperatures higher, to levels more commonly seen in July or August, if at all.
  • Climate change is likely playing a prominent role in this event.
  • In recent years, there has also been a trend toward stubborn and sprawling heat domes, which block storm systems and keep hot weather locked in place for days at a time. The current heat dome extends from the U.S.-Mexico border to the Canadian border.
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