Wednesday, August 9, 2017

It's stuck until Friday at least

The high pressure system over us is a slowpoke. By the time is vacates our airspace this weekend, it would have calmly resided over us for about 10 days. It not only brought us a heatwave but also the flow conditions that helped transport copious amounts of BC wildfire smoke here. Some cheek, overstaying its welcome!

Last evening's satellite picture (~4PM) shows much of the state socked in with smoke. Apart from the movement of some high clouds, the animation looks almost identical to this image. In other words, the ridge is preventing any substantial air movement. Air quality degraded yesterday and prompted the reinstatement of burn bans in the Puget Sound region and the issuance of an air quality advisory in Southwest WA.

So the forecast is for more of the same on Wednesday and Thursday. Western WA will see air between Moderate and Unhealthy, with coastal areas showing Good air. Eastern WA will rarely improve beyond Unhealthy for Sensitive Groups.

Morning fog has been present close to water for a few days now (see background view in the Nisqually webcam) and should not be confused with smoke.

Though the ridge S-L-O-W-L-Y moves east of the Cascades on Friday, there is no strong intrusion of marine air to rapidly clear the smoke from western WA. While air quality will start improving by Friday evening, models suggest that it might be well into the weekend before on-shore winds are able gather enough steam to flush out the smoke (image below shows surface winds on Sunday morning). Eastern WA will take even longer to clear out.

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