The inversion is strengthening up now...take a look at the latest observations from the Seattle profiler..which measures temperature above Sand Point (Magnuson Park area of NE Seattle).
Temperature drops off with height to about 1000 meters (roughly 3000 ft) and then increases
rapidly with height--that is the inversion. Above the inversion it becomes not only warmer, but clear and sunny (check the view from Crystal Mt). During this week the inversion should
strengthen and lower, so you can always get out of the murk by moving upward. One of my favorite things to do in this situations is to climb Tiger Mountain. One can bask in the warmth and look down on the clouds below (there is a picture from one of my ascents in my book)
Although there were a few sunbreaks today, I expect low clouds to reform over night. The air near the surface is relatively moist (dewpoints in the mid to upper 30s) and as the air cools down overnight the air will become saturated and fog will form. The problem with fog is that one formed it can become very peristent--solar radiation is reflected off its top (helping to cool) and fog is very good at radiating infrared energy to space (also cools). Sort of like a cloudy refrigerator! So you have a positive feedback that can keep cold, stable air near the surface. Another factor is that the ridging will amplify, producing more subsidence (sinking) aloft that will producing warming aloft and strengthen and lower the inversion. I hate to say it, but this is an ideal situation for us to fog in and stay like that. Our only hope is that there will be enough offshore flow to mix it out a bit during mid afternoons.
Sea Tac often fogs out in this situation...so call before flying out. Sea Tac has a worse fog problem than Boeing Field because Sea Tac is higher (452 ft). During the day the fog often lifts a bit...Boeing can open up enough for landings...but Sea Tac remains in the murk. Portland should be fine because the strong outflow winds from the Gorge.
Air quallity is generally ok now, but it will decline as the inversion strengthens and lowers. More on that tomorrow.
I wanted to mention that I will be giving a talk on Northwest Snowstorms at Third Place Books next wednesday (jan 21) at 7 PM. Will desribe the situations that give us snow here.