Unsettled weather this week as multiple systems impact interior Northern California. Rain and mountain snow are expected this evening into Tuesday. The second and more impactful system occurs Wednesday into Friday.
Discussion
Two main periods of unsettled weather are expected for interior NorCal this week, the first expected later today. An upper level trough begins to move onshore today, with showers beginning in the northern mountains and Coast Range as early as this afternoon, continuing to spread across the area tonight into Tuesday. The majority of precipitation will be seen in the higher terrain with only scattered showers expected for Valley locations.
The highest Valley QPF amounts expected in the far northern Sacramento Valley. Snow levels remain relatively high will this system, generally above 6500 feet, lowering slightly Tuesday afternoon to around 5500-6500 feet.
The bulk of the mountain snow is expected Tuesday morning, and a Winter Weather Advisory has been issued for 2AM-2PM Tuesday above 6500 feet in the Sierra Nevada where the highest snow amounts are expected. Sierra mountain travel may be impacted during this time as several additional inches of snow are forecast at pass levels.
Precipitation becomes scattered to isolated in nature by Tuesday afternoon with only some lingering mountain showers and showers over the northern Sacramento Valley.
Gusty onshore winds are also expected with the onset of this system, with winds picking up this afternoon continuing through Tuesday morning. The strongest winds will be in the central and northern Sacramento Valley, along with higher terrain. Expect widespread Valley gusts in these areas from 25-35 mph, and over higher terrain from 35-45 mph. Locally higher gusts expected over mountain crests. These onshore winds decrease Tuesday afternoon.
A brief lull, apart from a few mountain showers, will be seen Tuesday night into Wednesday morning before another system moves onshore. This system looks to be wetter than the early week storm and bring additional chances for rain and mountain snow.
Once again, the highest QPF amounts are expected in the northern Sacramento Valley and higher terrain. Periods of heavy mountain snow are expected at times beginning Wednesday afternoon and continuing into Thursday night. Snow levels fluctuate starting around 5000-6500 Wednesday, dropping to 4000-5500 Thursday morning, increasing slightly Thursday afternoon.
The lowest snow levels are expected in Shasta County and along the Coast Range while the higher end of those snow levels are expected over the Sierra and southern Cascades.
Total additional snow amounts could be over a foot in some locations. Be sure to keep up to date with the forecast if you have mountain travel plans this week. Precipitation does look to taper off on Friday.
Extended Discussion (Friday through Monday)
Ensembles support the trend toward a return to dry and milder weather across the region by the weekend with temperatures returning to a little above average by Sunday. However, cluster analysis continues to indicate some uncertainty on how quickly the late-week trough will lift out to the east, so we’ll maintain the NBM forecast of diminishing showers across the area on Friday.