fire danger

9pm Sunday…

I’m on vacation this week (at home for now), but we’ve got some serious fire weather ahead. First, while I’m standing in my kitchen about two hours ago, my wife’s phone gets an emergency alert. It came in with a blaring tone like a civil emergency or Amber Alert.

Other than the crisis of her phone having less than 50% charge, what does this mean? Power may be shut off in 24 hours? My phone didn’t receive this alert, but hers is probably pulling from a cell tower closer to Mt. Hood.

This is a first, I’ve never seen a situation where PGE has considered de-energizing power lines to avoid forest fires. Indeed, they have the “Hoodland Corridor” (east of Sandy to Welches to Government Camp) under this possibility

They are taking the proactive step after seeing what can happen with high winds, low humidity, and extremely dry vegetation. We’ve seen it in California the past couple of years. We get gusty easterly wind sometimes in September, nothing unusual, but this time is different. MODELS ARE FORECASTING A “HISTORICALLY STRONG” EASTERLY WIND EVENT BEGINNING MONDAY EVENING AND CONTINUING THROUGH TUESDAY

WIND HIGHLIGHTS

  • Nothing unusual through late afternoon Monday over and west of the Cascades. It’ll be a hot afternoon though, into the lower 90s in Portland.
  • Sometime around 5pm or so, a strong easterly wind will start coming over the Cascades, through the Gorge, and down into the lower elevations. Wind will be around through Wednesday.
  • DAMAGING WIND (gusts over 45-50 mph) should be confined to ridges in the Coast and Cascade Ranges, plus down into the Cascade foothill communities. That’s eastern Clark, Multnomah, Clackamas, Marion, & Linn counties. Wind gusts 40-60 mph are not a damaging wind in the western Columbia River Gorge.
  • I DO NOT EXPECT A “WIND STORM” IN PORTLAND, but gusts 35-45 mph are unusually strong for early September and some limbs will probably fall. Expect a few power outages Monday night and Tuesday.

THE BIG FIRE WEATHER PROBLEM

I’ve never seen a high wind setup (for the foothills and Cascades) this early in the “Fall east wind season”. This is unusually strong even for November/December, but this hasn’t happened when forests are still totally dry and humidity will be extremely low. This could be a once-in-a-quarter century type of event. I haven’t seen it in my 29 years forecasting here! The Storm Prediction Center has our area under an “extremely critical” fire threat; I don’t think I’ve seen that either

The problem?

  1. TERRIBLE TIMING: Forests are at the driest of the season…ready to burn. In fact a bit drier than average for early September. If this was May, we might be okay.
  2. DRY AIR: Relative humidity will plunge into the single digits to teens all across Oregon as dry air arrives Monday night. Almost unheard of west of the Cascades in September.
  3. STRONG WIND: Wind gusts 30-60 mph (depending on location) could whip any spark into a massive fire in a few hours in these conditions. Imagine if a Douglas fir branch drops onto a power line, bringing it down & starting a fire. 30-40 mph gusts could spread a fire many miles with downwind spotting. The Eagle Creek Fire on this date in 2017 spread 15 miles through the Gorge in one night! That COULD happen somewhere along the west slopes of the Cascades tomorrow night or Tuesday.
  4. HISTORIC SEPTEMBER FIRE TIME: The largest fires west of the Cascades have blown up under these conditions; Tillamook Burn in 1933, Yacolt Burn in 1902, Eagle Creek Fire in 2017 etc…

WHAT YOU CAN DO THE NEXT 2 DAYS

  • Stay out of the woods and travel only on graveled/paved roads. Never drive over grass once your vehicle warms up.
  • If you live in a rural/forest area DO NOT MOW or do anything outside that can create a spark during this time
  • No cigarettes, fireworks, or shooting practice (Pit Fire near Estacada started this way)
  • If you live in the foothills of the Cascades or western Gorge, be prepared to leave home quickly if needed and stay alert. I still have my camping trailer hooked up since we just got home. I decided to leave it that way until Tuesday night…just in case. It happened 3 years ago…

I won’t spend too much time on the technical details. We have a hot ridge of high pressure over the West Coast right now. Temps are running about 10 degrees above average and more like +15 coming up tomorrow. A 597 dm high is VERY hot. With offshore flow that could put us close to 100 degrees. But we had onshore flow today

The upper-air pattern becomes highly amplified (briefly) Monday night and Tuesday. An early season cold airmass digs south into the Rockies, doing a “drive-by” of the Pacific Northwest. This is 8pm Monday. That’s quite a setup, hot airmass along coastline and cool fall weather coming down through Idaho. This general pattern is perfectly normal in September/October, but this is an extreme version of that pattern

By Wednesday the hot upper high is back over us…other than fire weather the big story is a continuing hot/warm pattern through NEXT weekend.

To show the contrast between the “cold” airmass coming in to our east vs. the hot to the west. Take a look at 850mb map for tomorrow evening

About 35 degrees BELOW NORMAL at 5,000′ over Montana, yet 12 or so ABOVE NORMAL over the Oregon coastline. That’s a tremendous thermal gradient. So a dry cold front will push south and west across the Pacific Northwest tomorrow afternoon-night. You see the arrival in the WRF-GFS cross-section over Portland. Right around 00z tomorrow (5pm). 60-70kt wind speed around 3,000′ over Portland. That’s amazing; I’ve never seen that in September/October, and it’s very rare anytime in the cold season. So we’re in a bit of uncharted territory here. For example, how much of that strong wind will “mix down” into the valleys?

The same model shows the benign wind conditions at 2pm tomorrow. Northeast wind is just arriving at The Dalles and northeast Oregon. This is what we would call the “arctic front” if it was winter; the sudden wind switch to easterly. Note these are calculated wind gusts, not steady speed.

By 2am Tuesday (tomorrow night), high wind has arrived in the Cascades and gusty wind in most of the metro area as well. There could be some crazy strong wind gusts in the Cascades and western foothills. 50-65 mph possible there. Notice more reasonable wind in the metro area…gusts 25-45 mph; still strong for September.

Also note (in red) the 8-9 millibar easterly gradient across the Cascades; I’ve never seen that in September either. Right now there are two large fires burning in NW Oregon. One north of Detroit (Beachie), and one large one (Lionshead) just east of Mt. Jefferson. Imagine what could happen with either of these fires the next 48 hours. Not good..here’s the Beachie fire this afternoon from folks at Willamette National Forest

So, meteorologically we’re about to see something very rare for this time of year. IF we don’t get any large fires, it won’t go down in history as something that interesting for regular folks. But of course if we get one or more large fires, we’ll all remember!

Chief Meteorologist Mark Nelsen

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