December 31, 2018 – Gusty north to east winds will increase across the region today and continue into Tuesday before diminishing around mid-week. The first precipitation event for 2019 will be this weekend.
Discussion
Upper trough continues to dig southward to our east through the Great Basin. Satellite imagery shows clear skies across the region except for a few high clouds moving rapidly southward and clouds banked up along and east of the northern Sierra crest. The area of stratus that had extended north into the Sacramento region Sunday evening is being pushed southward into the San Joaquin Valley by strengthening northerly flow.
Little change to forecast. Northerly winds will increase and spread across the area today as surface gradients tighten and cold-advection strengthens. The strongest winds in the valley are expected this afternoon with gusts around 40 mph possible along the west side. Northeast winds are expected to peak later today and tonight across the west slopes of the northern Sierra with gusts of 50 mph or higher possible along the crest.
It will be a cold start to 2019 with minimums on New Year`s morning expected to range from the single digits to 20s in the mountains with mainly upper 20s to mid 30s in the valley. Highs Tuesday will feel chilly through the valley with the brisk north wind and readings in the upper 40s to mid 50s.
Dry weather with lighter winds and moderating temperatures is expected Wednesday and Thursday as ridging from the eastern Pacific moves overhead.
Extended Discussion (Friday through Monday)
An upper ridge initially parked over the southwestern U.S. will advance eastward in response to amplifying flow approaching the West Coast. While any precipitation chances should wait until the weekend, warm advection in advance of this trough will support an increase in cloud cover across Northern California on Friday. Run- to-run model comparisons show inconsistencies in the storm track this weekend which suggests reduced confidence in eventual impacts.
A shortwave which had been advertised to sweep through the region on Saturday has trended toward a more amplified scenario. The 06Z/00Z models show this trough digging farther south toward the southern half of the state late Saturday into Sunday. This ultimately would favor the heavier amounts over Southern/Central California although intermittent wet conditions are likely the second half of the weekend across the region.
In addition to the precipitation threat, gusty winds could return to the Sierra ranges. Dry conditions should prevail for much of Monday ahead of the next Pacific system taking shape offshore. This supports a potentially active pattern into the following week.