Today was a very different day than those of earlier this week in a number of ways. First, the fog and low clouds were considerably reduced west of the Cascades, particularly in the afternoon (see the sat picture at 2 PM). Low clouds did remain east of the Cascades and extended into the pass.
The pressure difference across the Cascades increased to 14 mb...higher to the east. This large pressure gradient helped to drive strong easterly winds. Some of these winds reached the surface over the eastern lowlands...from North Bend to Samamish..and when they did, the cold air was scoured out the temps jumped to near 60F. But nearly regions which remained in the cool air, below the inversion, were 10F or more colder.
The Seattle profiler showed the strong easterlies (actually southeasterlies aloft) and the profound change in the inversion and temperature structure aloft (see figure from 7 PM Sat to 7 PM Sunday). Last evening we had inversions galore... the old inversion aloft and a new radiation inversion at the surface (produced by radiational cooling at the surface). During the afternoon, the surface warmed up and the warm air above mixed down and the inversion become greatly weakened. With dry warm air mixing down, visibilities (from the Puget Sound Clean Air Agency webcams) soared....take a look at the difference between the visibility today at 3 PM and two days ago...pretty dramatic. You can see some of those residual low clouds in today's image.
As many of you have done, I hiked up Tiger Mt. today...from 500ft in the parking lot to 2522 ft at the West Tiger 3 summit...referring to a high-accuracy thermometer and an aneroid altimeter on the way up. We started at 9:10 AM--36F. There was a large temperature changed in the first 500 ft (to around 46F at 1000 ft). This was the surface-based radiation inversion. Then between rougly 1200 and 1900 ft the temp climbed into the mid 50s (the second inversion) and we entered the realm of the strong easterlies. At the top, the temps reached around 60F (high was 61.4). Excellent visibility in all directions. There was some snow on the shaded slopes in the last few hundred ft. I was impressed how much the snow level had risen on the Cascades...looked like 3000-3500 ft on the western slopes.
Looking at the computer models tonight...stuck by the lack of precipitation for the next week....nothing there really.