Active storm pattern will continue for the next week. First storm is moving through currently with strong winds and moderate to heavy precipitation expected into the morning. Snow will continue in the mountains through tonight.
Discussion
Strong storm currently moving across the region. Surface pressure continues to fall ahead of the strong mid/upper jet (over 100 kts at 500 mb) approaching the north coast. The strongest pressure gradient lies over the Sacramento Valley where the SAC to RDD gradient is currently 9.6 mbs. Wind gusts over 40 mph have been common (with a few gusts over 60 mph) over the northern half of the Sacramento Valley since late Monday evening and gusts over 30 mph are beginning across the Sacramento area. The axis of stronger winds will gradually shift south early this morning, and winds will begin to taper across the northern Sacramento Valley around daybreak. Winds are expected to decrease considerably by late this morning, though it’ll remain breezy today.
Radar shows a large band of mostly light to moderate rain moving across the area. There have been some embedded areas of heavy rain, but these have been brief across the valley. So far the only isolated minor flooding reports have been due to clogged storm drains.
In the Sierra, the Colfax snow level radar indicates the snow level is above 11k ft currently, but in reality it’s about 6 to 6.5k ft along I-80 where heavy snow has been occurring over Donner Pass since midnight. The forecast sounding at KBLU is pretty isothermal above 850 mb despite strong warm-advection, so snow may hang on near the pass level before snow levels drop behind the cold front at midday. So, we’ve pushed up the start of the Winter Storm Warning to early this morning where the combination of snow and strong winds will make for very difficult driving conditions.
The front is forecast to drop south of Sacramento this morning with light to moderate rain forecast to hang on into the afternoon across the northern San Joaquin Valley. To the north, breaks in the clouds will allow destabilization to take place over the Sacramento Valley with potential for a few thunderstorms by mid to late afternoon. Forecast soundings for the northern Sacramento Valley show considerable lower-level shear as surface flow remains backed beneath strong mid-level west-northwest flow. If sufficient instability develops for isolated thunderstorms, it appears there will be a non-zero risk for funnel clouds, or a weak brief tornado, in the area from Redding to Chico.
Showers hold on in the Sierra tonight into Wednesday morning, but dry weather returns elsewhere.
A weaker series of systems, but longer duration, moves in beginning Wednesday night and continuing into the weekend.
Extended Discussion (Thursday through Sunday)
The wet pattern continues late this week and into the new year. Ensembles are in good agreement that we will see a second storm bringing more widespread precipitation Thursday night into Friday as another short wave trough pushes to our north. Moderate rain and heavy snow can be expected at times again with this system.
A third more impressive storm will dig deeper and pull in higher moisture levels and we will likely see a period of moderate to locally heavy rain along with heavy mountain snow above 6,000 feet. Valley rain is projected to be around 1 to 2 inches. This storm system continues to favor southern areas with the heaviest precipitation expected from about I-80 southward.
Exact details remain unclear but confidence is good that the unsettled wet weather will continue. There could be a lull from rain and snow late Sunday and Sunday night as a short wave ridge builds in.
Additional systems bring the potential for more rain and mountain snow next week, with the unsettled pattern continuing.