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January 7, 2020 – Patchy fog possible through midmorning. Dry weather today. Light precipitation returns tonight into Wednesday and again Thursday. More widespread rain and mountain snow is possible with a cool system Friday into the weekend.
Areas of dense fog are being reported early this morning in the southern Sacramento Valley and northern San Joaquin Valley, and fog is expected to dissipate by midmorning. A Dense Fog Advisory is in effect until 10am. Dry weather will continue through most of the day as high pressure remains over California.
An upper level trough approaches the West Coast today, bringing increasing clouds to the forecast area. This is forecast to be a fast moving weather system, bringing a quick shot of precipitation overnight Tuesday. Up to a quarter of an inch of liquid precipitation is expected over the mountains with only a few hundredths up to a tenth of an inch forecast over the lower elevations. Only a couple inches of snow are possible above 4500 feet. Showers will linger over the mountains Wednesday with light accumulations expected.
Another quick yet colder upper trough is expected to move through NorCal Wednesday night through Thursday. Liquid precipitation amounts of a tenth of an inch of up a quarter inch are forecast. One to three inches of snow is expected above 4000 feet, with a dusting possible down to the upper foothills.
Dry weather returns briefly on Friday before a wetter winter storm is slated to impact interior NorCal Friday night through the weekend. See the discussion below for more details on this storm.
Extended Discussion (Saturday through Tuesday)
A semi-permanent upper trough setting up over the region should remain a fixture in the forecast from this weekend into the following week. Initial height falls accompanying the early weekend system will somewhat graze northern California with the stronger forcing up in the Pacific Northwest. However, enough energetics from the trough passage will still bring widespread precipitation to the area, especially over the higher terrain. This will not be a particular wet system with only 0.10 to 0.25 inches expected over the Sacramento Valley, perhaps lower to the south. Snowfall accumulations across the mountains should reach the 6 to 8 inch range above 5,000 feet with even a dusting down into the upper foothills as snow levels fall. Travel impacts and delays are possible this weekend so check back for future updates on the weather forecast.
Aside from snow showers across the mountains, much of the region should dry out for the first half of Sunday. Global ensembles continue to keep active weather over the region with additional impulses tracking down from the Gulf of Alaska. This will keep a threat for precipitation in play late Sunday into next week. In particular, model guidance has continued to advertise a more pronounced trough affecting the region early next week. While details will change, ensemble probabilities currently suggest a wetter system while snow levels remain on the lower end. Looking a bit further out, the Climate Prediction Center experimental Week 2 outlook is advertising wet weather out to January 16-18.