Mountain snow and valley rain showers return tonight along with breezy winds. Another chance for wet weather possible late in the week. Winter Weather Advisory from 7 AM Monday to 7 AM PST Tuesday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.
Discussion
Cool temperatures are widespread across Northern California this morning. Many locations are below freezing, including much of the Valley. Some isolated areas of low clouds have started to develop as of 2:00 am this morning. Satellite imagery shows low clouds in the northern most part of the Sacramento Valley as well as a small area in the San Joaquin Valley. HREF guidance indicates a chance for the low clouds to extend further into the Sacramento Valley this morning. However, dense fog is not expected to become widespread. Frost is likely this morning through the Valley as well.
High level clouds are also passing over the northern part of the state associated with a low pressure system to our northwest. Ensemble guidance is in good agreement this low will eventually bring unsettled weather to the region by later tonight through early Wednesday.
The coastal range, southern Cascades and northern Sierra will see the greatest impacts from this incoming weather system with gusty winds and several inches of new snow accumulation.
A strong upper-level jet is forecast to be over the CA/OR border leading to gusty winds, especially for the higher elevations. Gusts over the mountains could reach 40 to 50 mph, locally higher, for wind prone gaps and ridges.
The Sacramento Valley will also see chances for showers and gusty winds. There is good agreement in model solutions that a strong southerly breeze will develop through the central to northern part of the Sacramento Valley Monday with sustained winds over 20 possible. RDD to MFR gradients are forecast to reach 11 to 13 mb overnight Sunday into Monday. However, SAC to RDD gradients are not looking very impressive, therefore the strongest gusts will likely be confined to the northernmost part of the Valley. Gusts through the valley are forecast to range from 25 to 35 mph.
Precip accumulations are not expected to be very high especially for the Valley and areas south of HWY 50. Current forecast has a tenth to a quarter of an inch possible. The foothills could see up to a couple inches.
Snow levels will start out around 2500-3500 feet rising to 4500-5500 feet Monday. Several inches of new snow will be possible over the higher elevations with a couple of feet of new snow possible on the highest peaks and ridges.
Extended Discussion (Thursday through Sunday)
Ensemble guidance is in good agreement high pressure is forecast to build into the region midweek leading to a period of quiet weather for northern California.
DESI indicates some agreement about another chance for unsettled weather Thursday into Friday. Mountain snow and valley rain showers will be possible but are not looking very impactful at this time. Snow levels are forecast to be around 5500 to 6500 feet.
Thereafter, high pressure continues to build over the eastern Pacific leading to dry conditions for the remainder of the forecast period.