December 19, 2016 – Cool and dry weather for the most part this week. A couple of weak systems will bring some showers to the mountains, the first on Tuesday followed by another on Thursday.
Clear skies for the most part across interior NorCal early this morning with only a hint of a few high clouds approaching from the northwest. It’s another chilly morning across most of the region with current readings through the valley in the upper 20s to lower 30s, and with the absence of north winds temperatures are much colder along the west side and north end of the Sacramento Valley compared to 24 hours ago. On the other hand, thermal belt influenced areas of the foothills and west slopes of the northern Sierra are quite a bit milder with the ridge moving in.
While the ridge holds across NorCal today, mid and high clouds will be increasing from the north, especially north of Sacramento as a weather system moves into the PacNW. While we’re not expecting any precipitation this far south, the northern mountains and northern Sacramento Valley may see clouds thicken enough for some virga.
Enough cloud cover lingers tonight and early Tuesday that minimum temperatures are expected to be a little milder through the Central Valley. Some of the colder areas may dip down into the upper 20s early Tuesday morning, but most of the valley is expected to see minimums stay around the freezing mark or slightly above.
While dry and milder weather is forecast for much of interior NorCal this week, a couple more weather systems will clip the region, the first on Tuesday followed by another on Thursday. These will be rather fast moving systems with low QPF, so minimal impacts expected other than some light snowfall accumulations across the higher elevations.
Locally breezy north to east winds will pick up again in the wake of the first system for Tuesday night into Wednesday.
Extended discussion (Friday through Monday)
The best chance of region-wide precipitation arrives Friday- Saturday this week. Medium-range models have been struggling to find agreement and consistency with the handling of this system. The 00z GFS and ECMWF now look comparable (although the GFS is considerably wetter), bringing the system through the area mainly Friday into Friday night. If the current model projections hold, this system could bring a fair amount of snow to the mountains with rapidly lowering snow levels.
High pressure rebuilds over California later Saturday and possibly into Sunday. Longer range models are hinting at a deep closed low approaching the coast early next week. These types of systems are notoriously difficult to forecast for, so expect low confidence in the forecast with that system for the next few days.