Massive smoke plume sets its sights on Washington State

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As has been widely reported, a major wildfire crisis continues to unfold across the west coast. The stats are too numerous to list. California has now surpassed 2.5 million acres burned, the most since records were tracked (3 decades). Oregon is approaching 1 million acres. The town of Malden, Washington was destroyed on a day in which 300,000 acres burned in Washington State.

The human impact is also immense. A rising death toll, hundreds of thousands evacuated, homes and businesses lost, power outages, thick smoke blocking out the sun, and dangerously poor air quality. Not to mention the dread that many of us are feeling, knowing that the human-caused circumstances (climate change, forest management, urban sprawl) that set the stage for these fires will take decades or longer to reverse.

Here in Washington, where the impacts have generally been lesser than our neighbors to the south, many are wondering if portions of Washington eventually experience the extremely poor air quality that has been associated with some of the worst fires:

While the air quality will degrade in Washington, it is unlikely to be as bad as Salem, OR, which is much closer to a large fire.

The answer, unfortunately, is yes.

Lets take a look at the weather pattern. The west coast is stuck in an “omega block” pattern which, following the ‘588 dm’ height contour around the two blue cutoff low pressure centers, resembles the Greek letter Omega (or perhaps the Lululemon logo):

500 hPa geopotential height anomaly map for late Thursday night Sept 10, via Alicia M Bentley.

In addition to bringing Seattle a record high of 91 on Thursday, this blocking pattern has been maintaining the offshore flow that is fueling the wildfires and preventing any type of weather system from ending our wildfire-fueled misery.

Is this pattern about to change? Slightly. Between now and Saturday the omega block will weaken and move eastward just enough to allow air from the south and west move into Washington.

500 hPa geopotential height anomaly map for midday Saturday Sept 12, via Alicia M Bentley.

Usually, this type of “marine push” would be a welcome relief from the heat. However, with an upper-level high centered over Nevada, air will rotate around the high in a clockwise direction, bringing the smoke up from the south. Additionally, the recent easterly flow has pushed the plume of smoke well offshore, meaning that even the ‘marine’ air to our southwest has been contaminated.

The visible satellite around sunset on Thursday evening showed the huge plume of smoke, which looks as thick as clouds from a strong weather system, suspended ominously to our southwest. Portland, Vancouver WA, and Aberdeen were already under the plume.

Visible satellite imagery on Thursday evening

The HRRR-smoke model can give us an idea of what to expect in the next day or two.

The plume will reach the Seattle area by Friday afternoon:

HRRR-smoke vertically integrated smoke forecast for 5 PM PDT Friday 9/11

By midday Saturday the plume is expected to cover most of the state:

HRRR-smoke vertically integrated smoke forecast for 11 AM Saturday 9/12

Sometimes the vertically-integrated smoke is not reflective of conditions at the surface. But with the wildfires so close, it is not surprising that the model is also showing high near-surface smoke concentrations as well:

HRRR-smoke near-surface smoke forecast for 11 AM Saturday 9/12

Given this forecast, I was very concerned to learn that unlike previous heat/smoke episodes, Seattle is not planning on opening its cooling centers or smoke shelters. One hopes the city will quickly reverse this misguided decision on Friday.

When will the smoke clear out?

Tough to say. The good news is that the upper-level low over the Pacific is expected to meander closer to the coast by early next week. That should bring increasing moisture and the potential for some rain to the west side of the Cascades. The models have pushed back the timing a bit, but most ECMWF ensemble members are showing a couple tenths of an inch of rain for Seattle on Tuesday.

ECMWF ensemble precipitation for Seattle, via WeatherBell

Unfortunately, this is not nearly enough rain to put out the wildfires, and the continued southerly flow will keep the threat of smoke around into next week. Although hopefully the smoke will start to get better by Sunday-Monday.

One interesting side effect of the shift to westerly flow is that a portion of the massive smoke plume will get picked up by the mid-latitude jet stream. By next week, some of the smoke will be over western Europe. And judging by the model forecast below, it may be thick enough to be noticeably hazy at times.

2 comments

  1. Right…thoughts on the near-surface marine push stabilizing the airmass further? It could mean that things get a little worse in the next 24-36 hours before they get “better” in the Sun-Tues timeframe.

    Like

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