September 07, 2024

Oregon Smoke over Washington. Ends Monday.

 The visible satellite image this morning shows a plume of smoke over Washington, smoke that mainly originated over eastern Oregon.

The effects of the smoke were pretty obvious over western Washington, with an attenuated, red sun rising to the east this morning:

The smoke is thick enough that the intensity of solar radiation has decreased noticeably (see measurements at Seattle below for the last three days below).   That means we will be cooler today as a result. 



Air quality is good on the coast, moderate over the western lowlands and the Columbia Basis, and poor over sections of eastern Oregon

The laser ceilometers run by the Puget Sound Clean Air Agency clearly show the smoke moving in aloft.  Here is an example from the instrument at  Beacon Hill, Seattle. The time is on the x-axis (increasing to the right) and the y-axis is height in meters (3000 meters is about 10,000 ft).  Quite a deep layer of smoke is moving through overhead.

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Nearly all the smoke is coming from extensive fires in grass, bushes, and scattered trees in eastern Oregon (see current fire areas below).  Numerous lightning and human-ignited fires have occurred in the rangeland of eastern Oregon, with other fires over the southern Oregon Cascades.   The extensive, lush flammable invasive grasses (like Cheatgrass) are a real problem.


For most of the summer, the smoke from the fires did not influence western Oregon or Washington because winds generally move from west to east in our region.

But during the last few days, easterly winds have prevailed, associated with a thermal trough extending into western Oregon.     To illustrate, here is the forecast weather map at 850 hPa (about 5000 ft) this morning.  The solid lines are like pressure and you can see the wind symbols.  Easterly winds over northern Oregon and southern Washington.


Below are  the air motions at the same level (5000 ft) ....something called streamlines.   You can see why the eastern Oregon smoke is approaching us.



Fortunately, the situation is going to change during the next 36-48 hours.

Here are the streamlines showing airflow at 5 PM Sunday.  The wind direction has radically changed...now out of the Northwest.  That will blow the smoke away.


To show the improved smoke situation, let me display the smoke forecast (total in a vertical column) from the highly skillful HRRR smoke prediction model.  

This morning at 8 AM. Lots of smoke.


Tomorrow morning at 7AM, still smoky.


But by 5 AM Monday morning, the switch to northwesterly flow was doing its magic, with western Washington nearly clear of smoke.   Tuesday will be even better.

Relief is on the way!








7 comments:

  1. Being in Tacoma, I've noticed the invasion of the smoke, particularly yesterday while out filming. Right now at noon, it's very smoky and the sun is very much filtered and extremely weak. Even if we supposedly were to hit 91 yesterday, the house never felt overly hot late in the day.

    Wednesday, the day was the most clear, though even then, some filtering, but mostly due to the sun's angle in the sky at this time of year. Thus, when it was a warm as it was yesterday, the heat is not as oppressive as it could be otherwise.

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  2. Cliff, according the the fire map that you provide, the fires appear to be mainly in forested areas of the Cascades and Ochoco range. Although the Ochocos are in central Oregon, they are highlands with dense stands of ponderosa pine and western juniper. Unless I'm missing something, it seems unlikely that cheatgrass prairie is significant contributors to the smoke, relative to the burning timber which has far more fuel.

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    Replies
    1. Jerry, you are not correct. Rangeland vegetation (including cheatgrass) dominate the fire areas. Confirmed this with USGS land surface maps...cliff

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  3. It is possible to see where fire activity is. Go to:
    https://www.kasiaandjason.com/Wildfire-activity
    Find the line: MODIS 1 km resolution: Canada / USA
    click on USA and after the download, click on "Open file"
    Zoom in on your area of interest. There is not much "street view", so there is some ambiguity as to what is burning. Similar areas on the eastern side of Washington are mostly grasslands or "open" forest. I've helped re-veg in such an area. The trees (mostly) did not burn.
    A good experience/exercise is to visit such an area the following spring and walk the landscape. Take a hike – take a camera, lunch, and wear good boots.

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    Replies
    1. thanks John.... one can also go to the NASA Worldview website and view fire radiative emissions from several satellites. One rapidly learns than most of the fires are in rangeland or where rangeland extends into very "open" forest...cliff

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  4. Just to elaborate a bit more on some of the earlier comments - I don't think the livestock-cheatgrass-fire model is as applicable in central Oregon as in other parts of the arid west such as the Columbia Basin. For one thing the fires this month are occurring at higher elevations - 3000 to 5000 ft. or more - and on poorer, rockier soils - where native grasses and forbs have a bit more of an ability to compete with cheatgrass than at lower elevations. Second, much of the landscape in this region is vegetated by stands of western Juniper, a species that is found in only a few locations in Washington. Heavy grazing in the past reduced fuels, and thus fire frequency, which allowed flammable juniper seedlings to proliferate in areas where they had previously been only widely scattered. The dense growth of junipers, which utilize much of the soil moisture, has had a marked effect of reducing the amount of grass growth. These are the circumstances that can lead to large, high intensity wildfires when there are extreme conditions (such as relative humidities under 10%), and which, because they are consuming woody fuels such as juniper, have the potential to produce much more smoke per acre burned than a fire that is primarily consuming grass fuels. Mapping of cover of annual grasses can be found at this link: https://www.mrlc.gov/rangeland-viewer/, which does appear to show lower annual grass cover in central Oregon that in other parts of the interior NW such as the Columbia Basin and the Snake River plains.

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    Replies
    1. Ed.... I looked at a lot of surface images for the various eastern Oregon fires.....there does appear to be a lot of grass and range vegetation....either by itself and beneath relatively low-density tree cover, such as Juniper....cliff

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