During winter, most days feature westerly surface and aloft winds, although rainfall is restricted by the coastal mountains. On rare occasions, a block in the Gulf of Alaska will drive cold air from the continent west of the Sierra/Cascade crest, producing much colder than normal weather with either snow or clear skies. The coldest month on record has been January 1937 with a mean of and a maximum of . The coldest temperature on record has been on January 22, 1962, while the coldest maximum temperature was on December 21, 1990.
During winter, most days feature westerly surface and aloft winds, although rainfall is restricted by the coastal mountains. On rare occasions, a block in the Gulf of Alaska will drive cold air from the continent west of the Sierra/Cascade crest, producing much colder than normal weather with either snow or clear skies. The coldest month on record has been January 1937 with a mean of and a maximum of . The coldest temperature on record has been on January 22, 1962, while the coldest maximum temperature was on December 21 1990.