The smoky haze will continue through Friday and the air quality alert has been extended until noon Friday. This is the latest smoke flow prediction from the Canadian government. (Recorded from https://weather.gc.ca/firework/firework_anim_e.html?type=em&utc=00.)
According to forecasters, a strong upper level ridge will keep a dry stable air mass over Western Washington into Thursday. In the lower levels, weak onshore flow has resulted in some improvement in air quality along the coast and areas near the Strait of Juan de Fuca. In the interior the low level flow is not strong enough to improve the air quality and with the winds right off the ground a bit northerly, conditions deteriorated during the day on Tuesday. Many places in the interior from Seattle southward were reporting air in the unhealthy category Tuesday evening.
Northerly flow will continue to transport smoke into Western Washington from wildfires in British Columbia through at early Thursday. In addition, atmospheric ventilation in the interior lowlands of Western Washington will remain poor. Weak low level onshore flow will continue to bring better air quality to the coast and areas along the Strait of Juan de Fuca.
The smoke and hazy skies will continue to plague Western Washington for the next few days. A change to southwest flow will begin late Thursday and continue into Friday. Initially the flow will be light so it will take some time for improvements to occur. The increase in onshore flow at the lower levels will also take time to develop. For these reasons the air quality alert has been extended to noon Friday.