Was this weekend’s east wind event unusual? No, but we ARE lucky no large fires emerged in NW Oregon & SW Washington
The forecast played out very well these past three days...
- Dry easterly wind showed up and left right on schedule (Friday morning to Saturday evening)
- The wind was not too strong, note no wind advisories or high wind warnings across the region. That was expected
- Relative humidity bottomed out around 10-15% in the lowlands and foothills both afternoons as temperatures peaked.
- Onshore flow with higher humidity, cloud cover, and light wind arrived overnight. That ended this dangerous east wind episode.
As mentioned in previous posts...this was going to be (and ended up as) a relatively typical late summer/early fall east wind episode. The same wind speeds and temperatures in the 80s/90s just two weeks from now would be far less of a problem because (it’s assumed) rain will likely have moistened vegetation/forests. This time was a problem due to extremely dry fuels. Most of us west of the Cascades in the valleys haven’t seen measurable rain since July 6th...66 days.
That is probably coming to an end tonight because at least SOME measurable rain should fall.
If you want to take a look at an extensive recap of the September 2020 windstorm and fires, you can find it here: https://fox12weather.wordpress.com/historic-september-2020-fires-labor-day-windstorm/
How did this weekend compare? Not even close. At my home in the Cascade foothills a strong easterly wind never really surfaced. I think my peak gust was only around 25 mph. Last time was 49 mph. Some other locations
|Weather Station||2020 Peak Gust||Peak Gust Friday/Saturday|
|Portland Airport||52 mph||40 mph|
|Glenn Jackson (I-205) Bridge||60||35|
|Timberline Magic Mile Lift (7,000′)||106||58|
|Horse Creek Raws (in Cascade foothills)||66||36|
|Mt. Hebo (3,000′ in Tillamook County)||92||47|
Again, this isn’t a surprise; that Labor Day 2020 windstorm was a historic event! One other difference was the dewpoint & relative humidity. That airmass 2 years ago was much drier. Dewpoints down around 20 degrees; this time PDX bottomed out between 30-35 degrees. Still plenty dry to allow a fire to blow up quickly in the wind, but not as extreme.
So I’d say this event was a little stronger than a typical fall event, but nothing TOO unusual.
What made this event far different was the PSPS. Public Safety Power Shutoffs. Approximately 30,000 PGE and 12,000 Pacific Power customers had power cut at some point Friday through at least midday Saturday. Pacific Power had everyone back online yesterday evening, PGE has almost everyone back on as of 9pm this evening. Mine was off for about 55 hours. This is the first time power companies in Oregon have done a widespread shutdown. I don’t have any great insight into the reasoning, other than the obvious...tree branches can fall onto a powerline and start a fire. This has happened the past few years in California and during the Labor Day 2020 windstorm in Oregon.
I’ve never seen power shut off in the western Gorge with this strength of wind in the past, even when it’s extremely dry in September. For example the power was ON the night the Eagle Creek fire was racing through the Gorge 5 years ago (although wind not quite as strong). Something clearly has changed but that’s beyond my expertise...I’d better just stick to weather!
Good Fire Season News!
The very good news is that this episode was likely the peak of fire season and things die down from this point forward. It’s turning cooler, a few showers are moving through the region tonight and tomorrow, and there’s no sign of hot weather or dry easterly wind in the next 7-10 days.
There’s a very good chance that was our only “dangerous east wind fire weather event” of 2022. Last year we had showers before the easterlies showed up, so no big fire issue in September...it won’t happen every year. There are 2 huge fires (Cedar Creek & Double Creek) burning now that are consuming the most acreage...but even these should slow to a crawl the next few days. Growth this afternoon was far less under cloud cover and cooler temps down around Oakridge & Willamette Pass
That’s it for now...enjoy the nice early fall weather this week!
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