Excerpts from Jim Conrad's
from the July 24, 2005 Newsletter issued from the Sierra Nevada foothills
somewhat east of Placerville, California, USA
I had expected it to be cooler atop Slate Mountain. However, when I told Fred how hot it had been up there he wasn't surprised. He said that that morning he'd been listening to the helicopter-based traffic man on the radio flying above Sacramento in the Central Valley below. At 6 AM it had been in the upper 60s in Sacramento but 1500 feet above the valley floor the thermometer had read 95°.
At http://www.wrh.noaa.gov/sto/CWA.php NOAA provides a website describing summer weather patterns in the Central Valley and adjacent foothills and mountains. There they explain Fred's numbers as resulting from a "nocturnal inversion formed due to downslope drainage flow from adjacent mountain ranges."
That downslope drainage is also why each morning at dawn we have this brisk wind around us whooshing through the pines.