6:30 pm EDT
Most wildfire starts during Pacific Northwest summers occur on just a couple of days, when large dry lightning outbreaks impact the region. The most extreme dry lightning outbreaks can cause hundreds of starts over a period of hours. A moderate dry lightning outbreak occurred on August 9th and 10th, when a deep upper-level low offshore pulled monsoonal moisture originating from the Eastern Tropical Pacific and Gulf of Mexico northward.
Credit: University of Washington
The result was prolific lightning, with several hundred lightning strikes recorded on the 9th and 10th alone.
Credit: University of Washington
Credit: University of Washington
As the images above show, lightning strikes were observed over Puget Sound and the South/Central Willamette Valley. The storms east of the Cascades had more instability and more favorable dynamics (i.e. more of a rising motion in the atmosphere) to work with, and some of these storms had severe thunderstorm warnings for strong winds and large hail. Some impressive pictures circled around on social media after the storm, take a look.
Lightning strike framing Mt Jefferson during a thunderstorm yesterday near Warm Springs, OR #orwx #wxtwitter pic.twitter.com/OfdDzNQiFl
— Michael Trofimov (@pnwmiketrof) August 10, 2022
August thunderstorms in the Inland Northwest are beautiful but they are dangerous! #wawx #wawildfire @NWSSpokane pic.twitter.com/IeVesQbR2a
— Andy Brown (@otxwcm) August 12, 2022
Fires
While we can track exactly how many lightning strikes occurred with these storms due to the GOES-17’s “Geostationary Lightning Mapper” (GLM) instrument, It’s impossible to know exactly how many small fires were started by these thunderstorms and simply peter out later with little fanfare. The National Interagency Coordination Center only tracks “large fires,” which are wildfires of 100 acres or more occurring in timber or wildfires of 300 acres or more occurring in grass/sage.
Of the 6 current “large fires” in Oregon and 4 current “large fires” in Washington, all but 1 were started during another stretch of monsoonal thunderstorms experienced at the end of July/beginning of August. But I imagine that we’ll see new “large fire” entries from this most recent event as the recent starts grow in size.
With the hot, dry weather we’ve seen since the last week of June, even some of the larger fuels have turned very dry, and fuels are unfortunately expected to continue to trend even drier as we see another round of hot weather next week.
Credit: Northwest Interagency Coordination Center
Mid-August through September is our highest fire danger period of the year, and a major concern is having a dry, offshore windstorm cause small, lightning-caused fires to rapidly grow. This exact setup happened in 2020, where a lightning outbreak in mid-August resulted in numerous fire starts over the Cascades (including the Beachie Creek and Riverside fires), and then strong, offshore winds over Labor Day caused these starts and other human-caused starts to grow extraordinarily quickly, burning half a million acres over 48 hours. Let’s hope for the best, but prepare for the worst as we head into peak fire season.
