WeatherWatcher: Smoke clinging to the region

Tuesday, September 15, 2020

West Coast color satellite animated loop

Above: Sunday's animated satellite loop from the National Weather Service, showing all the active smoke plumes on the west coast. 

The forecast has changed: The bad news first. The smoke is not likely to clear out of the area until at least Thursday. The Puget Sound Clean Air agency has issued an Air Quality Alert that has been extended through Thursday evening. Levels of smoke in the air are Unhealthy to Very Unhealthy for all groups at this time and expected to remain that way through most of the week.

Smoke and its impacts on weather are not very well, if at all, anticipated by forecast models. The smoke on Saturday and Sunday was so thick that solar heating of the surface basically didn't happen. Instead the upper layers of the atmosphere warmed up, creating a temperature inversion that we normally only see during winter months.

Temperature inversions basically act like a dome, preventing any air mixing between upper and lower levels of the atmosphere. This has the effect of trapping all this smoke near the ground between our various mountain ranges.

As with many things this year, our optimism of smoke clearing out was destroyed when the storm we were expecting Monday night into Tuesday has changed direction and is now staying off shore. It is still getting close enough to set off some rain showers, but not enough for strong mixing winds to break up the temperature inversion.

What to expect: This smoke is going to linger for several more days. The storm system bringing us showers Tuesday through Thursday is slowly spinning off shore and expected to weaken as the week progresses. With little certainty the smoke might start clearing out by the end of the week but right now there is no solid indication on how this smoke layer will behave.

Isolated hit or miss thunderstorms are possible going into Thursday night and through Friday. Our chance of showers continues through Saturday, with a potential for a partly sunny Sunday. Temperatures are likely to stay below the 70°F mark through the weekend, with lows in the low to mid 50's.

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