Worst Is Over For Eagle Creek Fire, But Incoming Thunderstorms Could Start New Blazes

With our record dry summer and the hottest August on record for many places around the Pacific Northwest, we’ve inevitably had an incredibly active fire season and the smokiest summer I can ever remember seeing west of the Cascade Crest. The latest major blaze – the Eagle Creek Fire – came uncomfortably close to home, resulting in mandatory evacuations as far west as Corbett. Strong easterly winds not only exacerbated fire conditions, they blew uncommonly thick smoke into Western Washington and Oregon – so thick that we’ve had ashes falling from the sky for the past three days. And with frequent lightning in the forecast for parts of the area from late tonight through Friday morning, it looks probable that a few new blazes will ignite before the weekend.

There’s so much going on here that it’s tough to know where to start, and I’ll have to exercise some restraint as to not turn this blog post into a novel (post-draft proofreading edit: I failed). But let’s start by looking at some incredible images taken from the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument aboard NASA’s polar-orbiting AQUA satellite. The image directly below was taken on September 4th and shows just how far-reaching the effects of the fires throughout the West have been. Westerly winds aloft carried thick smoke originating from fires over the Intermountain West all the way to Chicago and beyond.

By September 5th (yesterday), upper-level winds helped to disperse the thickest smoke over the Midwest, but air quality worsened in the Northwest as multiple blazes continued to burn under a stubborn ridge of high pressure. Air quality was “unhealthy” around the Portland area, with falling ash and the visibility dropping to 3 statute miles at Portland Int’l Airport.

As bad as it has been in Portland, air quality is far worse in over Southern Oregon closer to the massive Chetco Bar fire (as well as numerous others) and in mountain valleys across the Pacific Northwest, where smoke tends to settle.

The latest METAR (Meteorological Terminal Aviation Routine) report from the Medford Airport reports visibility of a half mile, and the AQI (Air Quality Index) there is “hazardous,” the highest rating on their scale. Wizard Island is just barely visible through the Crater Lake webcam if you look extemely closely… compare a shot from two winters ago during good visibility to the most recent shot this afternoon!

The Eagle Creek Fire

The Eagle Creek Fire is the first wildfire in the western end of the Columbia River Gorge since the Falls Fire of September 1991, which formed near Multnomah falls and traveled eastward in the direction of Corbett (thank you Mark Nelsen for this tidbit, be sure to check out and subscribe to his awesome weather blog!). It was first ignited on the afternoon of Saturday, September 2nd by the illegal use of fireworks, and it quickly ballooned to a massive, 3,000 acre blaze by Sunday morning.

Beginning late Sunday/early Monday morning, a thermal trough began to form over the Willamette Valley, setting up offshore gradients and allowing strong, hot, and dry easterly winds to whip through the Gorge. Gusts at Crown Point topped out at 42 mph early Tuesday morning, which is pretty darn impressive for a summertime east wind event (they can reach 100 mph in the winter!). As a result, the fire grew to 30,000 acres and raced westward, traveling 15 miles from Eagle Creek to slightly east of Latourell Falls in less than 24 hours (again, credit to Mark Nelsen for this tidbit)! The fire even crossed the Columbia River into Washington, showing how winds not only add additional oxygen to an existing fire but start new ones by transporting embers.

The Monday night-Tuesday morning timelapse from the Stevenson, Washington webcam along the Columbia River looking south into Oregon is nothing short of apocalyptic.

Thankfully, the worst is over – winds have weakened significantly, and cooler, marine air associated with an upper-level trough is on the way. Unfortunately, most popular hiking spots between Bonneville Dam to just east of Crown Point have been overrun by the fire. Even though the area around Multnomah Falls was scorched, firefighters did an amazing job keeping the lodge itself safe.

Incoming Thunderstorms

The combination of a hot upper-level ridge to our east and a cool upper-level trough to our west is a classic setup for summer thunderstorms, as it directs warm, moist, and unstable air from the south into the region. Some thunderstorms have already started developing over Southern Oregon and will continue to track to the NW as the night goes on.

These storms are forming along an axis of enhanced upper-level vorticity (spin) ahead of the parent upper-level trough, which is currently located about 100 miles SW of the Bay Area. This axis will lift north throughout the night and will be positioned over Portland by sunrise tomorrow, but I believe storms will dissipate as they head towards northwards simply because they will be entering a more stable environment that is less favorable for thunderstorm development. Convective available potential energy (CAPE) is one measure of instability, and as you can see, there is no CAPE over the Portland metro area tomorrow morning. No CAPE, no thunderstorms.

I believe a better chance for thunderstorms in the Portland metro area will come Thursday night as the parent upper-level trough comes through and we have more instability, though it will still be significantly less than the atmosphere to our south. This morning’s WRF-GFS run from the University of Washington showed a very impressive multicell cluster of thunderstorms forming near Medford tomorrow evening and weakening as it traveled northward tomorrow night, yet perhaps retaining enough strength to give some light precipitation and a few lightning strikes to the Portland metro area. Both the Washington and Oregon Cascades have a much better chance of thunderstorms due to the enhanced instability and convergence over them.

Our thunderstorm chances end Friday morning as this trough passes through. We should see gradually improving air quality throughout the weekend as we enter a more zonal pattern with stronger onshore flow. Another ridge builds over us to begin next week, resulting in another increase in fire danger, so let’s hope for as much rain and as little lightning as possible this weekend.

I’ll have an update on Irma in the next couple days, which is now impacting Puerto Rico and is still packing sustained winds of 185 mph offshore. So much to blog about, so little time!

Cheers,
Charlie