January 12, 2019 – Much of the weekend will be dry until precipitation moves into the western Valley and Delta by Sunday evening. Significant wet weather returns to the region next week with multiple chances for heavy precipitation, including mountain snows, and gusty winds.
The upper pattern along the West Coast features a forming rex block as a series of lows undercut a persistent ridge centered over around Idaho/Montana. The initial closed low is currently swinging through Southern California which has cleared the region of any lingering shower activity. Given ample ground moisture and occasionally light winds, some fog has formed, particularly over the northern San Joaquin Valley. This should erode given daytime heating as any radiation inversions mix out. Overall, the closed ridge over the Upper Intermountain West should gradually extend southward allowing for a mostly dry weekend along with mostly sunny skies.
A shift in the pattern is expected by late Sunday as a deep, broad upper low slides southeastward toward the region. Chances for precipitation increase from west to east beginning across the western Valley and Delta region Sunday evening. By Monday, more widespread precipitation will move through Northern California as the parent upper low becomes nearly stationary off the coast. A more potent embedded shortwave pivots through on Tuesday affording a threat for moderate to locally heavy rainfall and mountain snows. Ultimately, snow levels should bounce around a bit but should stay somewhere around 5,000-5,500 feet. In addition to the increase in precipitation chances, a tightening pressure gradient will bolster wind fields across the region. At this time, the highest wind gusts over Valley locations could reach 25 to 35 mph with perhaps numbers closer to 45 mph across the mountain ridgetops.
Extended Discussion (Wednesday through Saturday)
Wet and windy system still expected Wednesday/Thursday next week with snow levels around 5-6K feet resulting in travel impacts through the mountains and potentially a strong wind event for the valley on Wednesday night, though plenty of uncertainly continues with models varying on the strength and location of incoming surface low. Ridging toward the end of the week may allow a period of a few days to dry out heading into next weekend, though confidence in timing that far out is low at this point.