A pattern change is expected to take place this week that will bring long-awaited rainfall to the West, including California, and relief from the blasts of cold air in the central United States. For much of November, a southward dip in the jet stream has been in place over the central and eastern U.S. This has brought rounds of cold air, along with periods of rain and snow. In the West, the dominant pattern has been dry and mild conditions due to an upper-level ridge of high pressure near the West Coast.