The inversion aloft has been progressively lowering in altitude. The picture below is extraordinary in showing this. What you are seeing are temps and winds above Seattle ( red temp, blue wind) over the past day. The zone of big changes in temperature (lots of red lines close together) is the inversion. Note how it has progressively lowered...right now the base of the inversion is around 600 m. The plots of temperature at particular times (second plot below), shows the inversion changes even more graphically. Within rougly 300 m (1000 ft), the temperature increases nearly 20F (10C)! I bet the top of Tiger Mountain (2500ft) is in sun now (let me know if anyone has been up there this afternoon).
Above the inversion it is really warm and toasty. The observations at Paradise (around 5500ft) showed temps in the mid-50s. This will be true for a number of mountain locations (e.g, Mt. Baker, Crystal). So this is a good time for a mid-elevation hike or ski trip in the mountains.
Air quality has held out...mainly because the inversion has been quite high, allowing the mixing of pollutants in a substantial volume of air (see graphic from Puget Sound Clean Air Agency). With lots of clouds we have not formed a surface-based inversion, and such inversions are associated with the worst air quality situations. However, as the overlying inversion descends, air quality may well decline.
The current long-range forecasts, out 4-5 days, are emphatic that high pressures and resulting inversions will hold out through the period.
