Temps drop in Portland; Winds set up ornery fire behavior


Details for Wednesday, July 14, 2021

PORTLAND, Ore. (KOIN) – A turn to cooler summer days is just about here, with temperatures dropping a healthy 5 degrees or more west of the Cascades. This will put us near our July average, instead of running a bit warm out there.

Expect morning clouds to move in again, as the onshore flow (wind coming in from the west) increases. Expect temperatures to still be in the 50s after sunrise, with a morning that will take some time to warm up because of thicker clouds. That cloud coverage may even bring in some patchy drizzle at times for the Oregon coast.

Clouds escape the forecast by Wednesday afternoon, bringing temperatures to the upper 70s by the afternoon, topping near 80. The wind is mainly running out of the northwest, just like the last week or so, not much stronger than 5 to 10 mph. This is prime weather for going for a bike ride or just hanging outside for an extended period of time for a hike or to play some sports.

Here is an idea of the morning clouds in the valley and the patchy drizzle out near the Oregon coast.

The clouds again stop short of about Marion County, allowing for temperatures to be warmer to the south. Cooler air aloft will keep conditions from reaching those 90 degree afternoons in Salem, a forecast that has been awfully consistent this July. Not a cloud in sight east of the Cascades, unless it is a cloud that develops because of the local wildfires.

You can expect smoke to move in and out of the region east of the Cascades through the remainder of the week. We won’t see that here in the valley, but areas closer to the wildfires will definitely have air quality and smoke issues. We will discuss that more in the section below. With more clouds and cooler temperatures west of the Cascades, it will actually turn the wind up on the other side of the mountains.

With that concern, the National Weather Service over in Pendleton has issued a red flag warning for Wednesday and Thursday. This is because of the gusty conditions that will push 30 mph to even 40 mph in the zone in pink below. That includes Pendleton, The Dalles, Madras, and all the communities in between. Not only is it going to be breezy but it is also going to be dry. These are also the locations for most of the active wildfires in the state right now.

This is the type of forecast that we don’t typically want to see in the summer. We need that cooler air to find a way east of the mountains to help the relative humidity out at night.

This is a weather model for Thursday afternoon, showing the wind and the relative humidity for Thursday. If you want to learn more about how relative humidity and wind impact wildfires, you can visit this article.

For those of you in Jefferson County or around areas of the eastern Gorge, conditions may be dry enough to the point where the relative humidity is down in the lower teens or single digits. This is why the National Weather Service put the whole area in a red flag warning for Wednesday and Thursday. Conditions are favorable for rapid-fire spread and it will likely support moments of ornery fire behavior around the region.

Take a look at the surface smoke forecast for Wednesday afternoon. Thickest smoke again near the Bootleg Fire, bringing the surface smoke forecast all the way to the very high category. With the wind running out of the northwest at the surface, it will push that smoke near the surface to the southeast. It looks like the smoke will impact Burns and Baker City on Wednesday, too.

Weather models are even coming up a steady column of smoke from the new Bruler Fire in Linn County just south of Detroit. If you’re traveling west, you will notice the smoke starts to clear out. For those of you that are traveling east from the valley, you will notice that the smoke increases.

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