The National Weather Service has issued a frost advisory for the Bay Area on Monday from 3 a.m. to 8 a.m. although the official forecast still predicts a low temperature of 38 degrees overnight for Pleasanton and the Tri-Valley.
That was also the prediction last night but at 6 a.m. some thermometers in Pleasanton were near the freezing mark at 33 degrees.
The weather bureau said Sunday afternoon that a cool, dry air mass combined with light wind and clear skies could result in cold temperatures late tonight and early Monday morning.
Temperatures in the coldest valleys in Alameda and Contra Costa counties are expected to drop to near freezing for a few hours Monday morning around sunrise, according to forecasters. Sensitive outdoor plants could be damaged or killed if left uncovered.
After sunrise, Monday will be bright and sunny with a high temperature of 68 by mid-afternoon with light and variable winds expected.