Unsettled weather will lead to chances for periods of generally light rain and mountain snow over Northern California at times this week. Precipitation be limited to the northern mountains early this week becoming more widespread mid-week.
A weak system brushing by to the north is bringing some light precipitation to the Coastal Range, southern Cascades and northern Sacramento Valley. Amounts have generally been several hundredths of an inch, with 0.02″ at Redding Airport. Mesoscale models suggest much of the rest of the precipitation will be this morning over western Tehama and Shasta counties, with snow levels around 4,000 feet. Skies should clear in the afternoon over much of the area, with mostly sunny conditions.
Highs should be 4 to 8 degrees warmer than Saturday overall, with the Valley and Delta warming to the upper 60s to near 70.
Another shortwave wave passes to the north, with the tail end possibly bringing some precipitation to far northwestern California on Monday. Interior Northern California should stay dry with just some increasing clouds late day Monday and cloudy skies on Tuesday.
Temperature will be rather mild with widespread low to mid 70s expected across the Valley and Delta Monday and Tuesday. Overnight lows will also be near to slightly above normal for this time of year, quite a change from the record lows last week.
By Wednesday much better chances for more widespread showers across Northern California develop as a deep longwave trough approaches with a surface cold front moving inland through the day. Snow levels start fairly high, around 7,500 feet then drop overnight into Thursday.
Precipitation amounts should generally be light, with some briefly moderate rain over the northern Sierra. Some light pass level snow is possible after midnight.
Extended Discussion (Thursday through Sunday)
Quite a bit of uncertainty still in the details of the late-week trough. Remarkably, cluster analysis indicates about equal chances between four scenarios for the trough on Thursday (00Z Friday) with significant differences in its strength and timing.
All would likely result in cool and unsettled weather, but only about a quarter would lead to more impactful winter weather. Trough likely shifts east by next weekend, but some uncertainty on how long the cool and unsettled weather lingers in its wake over the northern Sierra Nevada.