Eagle Creek Fire Weather Update: No Strong East Wind Expected

September 9, 2017

8pm Saturday…

I’ve been receiving a few emails and text messages from friends and viewers the past 24 hours.  Most of them (for good reason) want to know “when the dry and gusty east wind is coming back”.  There is good news again this evening; I DON’T EXPECT A RETURN OF A STRONG & DRY EASTERLY WIND, LIKE WE SAW THIS PAST MONDAY, FOR AT LEAST THE NEXT WEEK.  There is going to be some wind early in the week, but nothing like what almost became a firestorm Monday night.

Here’s where things stand as of Saturday evening:

  1. The fire has only grown on the southern and eastern end the past few days because we’ve been under a westerly wind pattern (as expected).
  2. Luckily this pattern has been quite cool (compared to the past 5 weeks) and mainly cloudy.  At 1,800′ there is a weather station at a home on the west side of Larch Mountain.  After days and days of temps in the 80s, the past 3 have all stayed at/below 70 degrees with relative humidity often up in the 60-100% range; that’ll bring fire activity way down.
  3. The western end of the fire is just smoldering and creeping with very little smoke seen west of Angel’s Rest.
  4. There is concern that a renewed hot/dry easterly wind could allow the fire to take off again and head to the west.  As a result firefighters plan to hold the fire east of Palmer Mill Road which I’m also told happens to be the fire line where the 1991 Falls fire was stopped.  They have been working there fixing the road and cutting lots of brush/trees.  Interesting that it was the same weather pattern 26 years later; and the same place the fire petered out last time.

Here’s a map of the eastern half of the fire, click for a larger view:

and the western end, closer to the metro area:

The red is the fire perimeter, which pretty much hasn’t changed at the west end since Tuesday when the east wind died.  I’ve added the blue line, which is Palmer Mill Road.  Now let’s talk weather.  The yellow area is the “east wind zone” on the Oregon side during just about all east wind events; winter AND summer.  Easterly wind, which is actually northeast wind due to orientation of the river, sticks quite close to the Columbia River until it gets around Rooster Rock State Park; always less than a mile or so from the river.  At that point the Columbia is about to enter the Willamette Valley and the hills become much lower (less than 2,000′).  The wind spreads much farther from the river, maybe 3 miles south of the river once it gets to Troutdale.  The homes/properties south of the yellow hatched area rarely get east wind (and didn’t last Monday).  These are great places to live if you don’t like that cold winter wind and also quite a bit safer since a fire wouldn’t come roaring in on wind.

So the big question is…“will we get a bunch of strong wind in the next few days?”  I think that’s unlikely.  Models all bring upper-level ridging (hot high pressure) overhead later Sunday through Tuesday, then that’s followed by more cool upper-level troughing toward the middle of next week.  Folks it appears fall weather is arriving.  That means brief warm periods followed by cooler weather as we’ve seen the past few days.   On Monday and Tuesday we’ll get well into the 80s, even a 90 is possible, so summer wants to have one last gasp.  Yet the pattern is not conducive to a gusty easterly wind coming down the Gorge due to it being a “flat” upper-level ridge.  Take a look at the cross-section over Troutdale for the next 3 days.

Time goes from RIGHT TO LEFT; right side was 5am this morning, 10/12=Sunday AM, 11/12=Monday AM, 12/12=Tuesday AM.  Wind flags show the wind direction.  Colors are relative humidity.  The “850” horizontal line partway up is around 5,000′ elevation and you can see the surface (where we live) below.  Note the high humidity through Sunday morning then we dry out quickly (afternoon sunshine!).  But wind flow is still westerly (onshore flow).  Monday morning through early Tuesday we go into an east wind pattern.  Yet the wind flow is not very strong.  This would give gusts maybe 20-30 mph around the ridges at the west end of the Gorge, but not the big 40-50 mph gusts we were seeing up there last Monday.  Still 20-30 mph is enough to keep a fire moving along the ridges.  I’m not a trained fire weather forecaster, but I would assume unburned areas of trees could ignite again under these conditions.  But there’s no reason to think with a weaker wind in the exact same location, that the fire would spread farther than last Monday.  It’ll still “run out” of that dry east wind in the same spots.  Hopefully that makes a bit of sense.

To summarize, I think we’ll get through Monday and Tuesday without a major increase in fire acreage.  But, for good reason, I’m guessing emergency managers will prefer the Level 3 people remain out of the area until after this east wind period passes by Tuesday evening.  We’ll find out the next 2 days at their press conferences.

As for rain, we’re getting some showers for the 2nd time this week this evening.  It’s just a few light showers, but it’ll wet the dust again.  Any rain is good.  At this point the next chance for a soaking appears to be about a week from now.  The ECMWF ensembles show some rain late next Sunday or Monday, kicking off a cooler/wetter period.  It’s possible that Tuesday will really be the last of our summer weather.  Enjoy the sun Monday and Tuesday!

 

Here is some more good news…great pics from Tessie Adams with Corbett Fire (Multco District #14) taken Friday:

Multnomah Falls area looks pretty good!  A lot of the fire must have run beneath the tree canopy in some spots and then torched from one crown to another in others.

As in this pic taken alongside the old Scenic Highway, note the mainly green trees above and burned brush below

Chief Meteorologist Mark Nelsen