Dry weather continues through Saturday. Cold nights through Saturday night. Rain and snow chances return by Sunday with wet weather continuing next week, with gusty winds at times. Mountain travel will likely be impacted.
Discussion
While skies are generally clear over the area, IR satellite imagery indicates a narrow band of fog and low clouds over the eastern side of the Valley from around Chico southward. Some visibilities down to 1/4 mile have been locally observed at Lincoln, Mather, Chico and briefly at times over McClellan Airport, with some mist elsewhere. North winds have been limiting the development of dense fog to areas to the west. HREF continues to show this trend with fog and low clouds on the east side breaking up by around 11 Pm.
Current IR satellite is showing some fog in mountain basins impacting towns such as Burney, Quincy, and Burney and this could persist into the early afternoon. Temperatures at 3 am PST were quite cool, about 5-10 degrees lower than yesterday. For the Valley this means temperatures already in the mid to upper 30s. Temperatures could drop to freezing and even locally into the upper 20s in a few wind sheltered areas. Areas of frost are likely across the Valley, Delta, and foothills.
Ensemble guidance remains in good agreement that cold temperatures continue over the next few days under upper level ridging with mostly clear skies. Sub-freezing low temperatures remain possible in the Valley, in particular the northern and central Sacramento Valley. Frost is likely to develop. More extensive morning fog is expected over the weekend, with lighter winds.
Sunday should be a transition day with the potential for light precipitation gradually spreading into Shasta County during the day as a weak system brushes by over far Northern California.
A cold upper low from the Gulf of Alaska approaches Sunday night into Monday, with precipitation chances gradually spreading south and eastward. This could become widespread across the area by Monday night, though ensemble members show uncertainty with a range of onset times.
Snow levels could start below 3000 feet and locally lower with entrenched cold air remaining, particularly in mountain basins. Snow could begin to bring travel problems to the northern mountains starting Monday, though higher potential for this will come later.
Extended Discussion (Tuesday through Friday)
Ensembles and clusters continue to be in reasonable agreement with longwave troughing developing just off the West Coast and slowly nudging inland next week. This pattern will bring periods of widespread precipitation to the region. Cluster analysis suggests some differences regarding the progression and position of the trough as some clusters are wetter or drier than the multi- model ensemble.
Nevertheless, NBM guidance favors a couple of inches of rain in the Valley/foothills as well as significant mountain snow above 5000 feet. NBM probabilities show at least a 40%-60% chance of seeing more than two feet of snow over the Sierra and southern Cascades through Thursday afternoon. This will likely disrupt holiday travel. Periods of gusty southerly winds are also possible next week.