The view looking northward over Lake Washington early this evening was dramatic and included towering cumulonimbus towers, some reaching 20-30 thousand feet (see my picture below).
A sure sign of a very unstable atmosphere.
An unstable atmosphere has a lot of vertical mixing, with rising air associated with cumulus clouds and sinking air in between them, marked by clear skies. An unstable atmosphere is associated with large decline of temperature with height, with warmer temperatures near the surface and cooler temperatures aloft.
And that is what we had this afternoon. The temperatures of the eastern Pacific are relatively warm, with offshore weather temperatures around 60F. Not Hawaii, but warm for us, following summer and early fall solar heating.
At the same time, a slug of cold air moved in aloft associated with an upper-level trough moving in off the Pacific (see temperature map for around 5000 ft for 11 PM today). The colors show the difference in the temperatures from normal, with light green being the coldest.The instability was so great that the resulting thunderstorms produced substantial lightning (see below, x indicates a lighting stroke).