January 3, 2020 – Dry and mild weather into the end of the week. Precipitation chances return this weekend, mainly north of I-80. Unsettled pattern possible by midweek, mainly over the mountains.
High level clouds continue to stream into the region early this morning, with current temperatures running a few degrees warmer compared to 24 hours ago. Locally dense fog is being observed across portions of the northern San Joaquin Valley early this morning. Conditions are drier across portions of the southern Sacramento Valley and the Delta compared to 24 hours ago; therefore, significant reductions in visibility are not currently being observed. Guidance suggest fog should be dissipating by mid morning.
Dry conditions will prevail across the region today under upper level ridging. Mild temperatures are expected once again today, with Valley highs generally in the upper 50s to mid 60s. These forecast highs range from 5 to 10 degrees above seasonal normals. Increasing cloud cover is expected today ahead of the upcoming system.
A shortwave trough will bring precipitation late tonight into Saturday morning, mainly north of I-80. QPF amounts will be light, generally ranging from less than 0.10 inches to around 0.35 inches. Best precipitation chances will be over the mountains, especially Saturday morning. Snow levels will range from 4500 to 6000 feet, with only light snow accumulations expected. Showers should be tapering off in the afternoon. Another short wave trough will pass through the region late Saturday into Sunday. Shower chances appear to be limited to the northern Sierra and the northern mountains, with light precipitation amounts. Ridging rebuilds early next week, ending precipitation threat.
Extended Discussion (Tuesday through Friday)
Ensemble models continue to show a weak weather system moving through NorCal Tuesday. Precipitation is expected to remain in the mountains and northern Sacramento Valley with light accumulations up to a quarter of an inch of liquid precipitation. A couple inches of snow will be possible for elevations above 4500 feet with lighter accumulation possible down to 4000 feet. Light showers could linger in the Sierra Wednesday with better precipitation chances Thursday for the mountains and Shasta County.
Ensemble guidance indicates the possibility for an upper trough sliding through the PacNW and deepening in the Great Basin area, bringing more widespread Valley rain and mountain snow to NorCal Friday through the weekend. At this point this system does not look particularly strong, but confidence is low in forecast details due to model inconsistencies. Keep an eye on the forecast for updates.