December 16, 2019 – Dry weather will continue with cold mornings through Tuesday. A weak system moves through mid-week with precipitation chances increasing by the weekend.
Discussion
A few high clouds are spilling through the amplifying eastern Pacific ridge into NorCal, otherwise skies are clear early this morning. Temps are chilly with most areas running colder compared to 24 hours ago. Current readings range from around 10 in the colder mountain valleys to the lower 40s across milder portions of the Central Valley.
Dry weather will continue the next couple of days as the short- wave ridge moves overhead. Highs will be close to average for mid-December while overnight lows will be slightly below average. Colder portions of the Central Valley will dip down to around the freezing mark by early Tuesday morning.
The next upstream trough is forecast to split with the southern portion moving into central California Tuesday night into Wednesday. We’ll likely see some scattered showers with light QPF across the region, but both the GEFS and EC ensembles indicate better potential to our south.
Focus of precipitation is then expected to shift back into the northern mountains and northern Sacramento Valley on Thursday as warm-advection and moist west-southwest flow returns. The southern half of the Sacramento Valley and northern Sierra south of I-80 will likely remain dry.
Extended Discussion (Friday through Monday)
Except for some possible light showers over the northern mountains, dry weather will prevail on Friday. Then, widespread precipitation could return next weekend as upper troughing develops. However, model differences are evident regarding timing/QPF amounts. Precipitation may spread into the region as early as Saturday afternoon over the Coastal Range, and gradually spread southward overnight. Ensemble guidance suggests moderate to elevated probabilities of total QPF > 1″, mainly north of I-80. Snow levels are expected to be around 5000-6500 feet Saturday, and are expected to fall to around 4500-5000 feet Sunday. This system could lead to travel difficulties over the mountains, especially since it is the pre-holiday weekend. Precipitation chances could linger into early next week.