March 5, 2020 – Dry through Friday with above average temperatures. Precip chances return Friday night into the weekend with accumulating snow across the higher elevations.
Discussion
Broad ridging covers the region providing clear skies early this morning. Surface pressure gradients are much weaker compared to 24 hours ago and winds are generally light except for some local gusts in the teens mph across the foothills and west slopes of the northern Sierra. Current temperatures range from the mid 20s in the colder mountain valleys, to the mid 40s to mid 50s across most of the Central Valley.
Slight cooling expected across the area today as the upper ridge axis shifts east resulting in minor height/thickness falls, and also allowing a return of onshore flow into the Central Valley. The SFO-SAC gradient has also turned positive and winds at Travis AFB have been gusting above 20 kts at times since midnight.
Changes take hold Friday as the approaching longwave trough brings an increase in cloud cover and cools temperatures off. The marine layer is forecast to deepen several thousand feet by 12Z Friday with stratus likely intruding into the Sacramento Valley Friday morning.
While quick moving, the southern extension of this trough should bring a round of precipitation to NorCal beginning Friday night. The bulk of the precip is expected on Saturday before winding down Sunday morning.
After a record dry February in many Valley/foothill locations, at least a little measurable precipitation is expected over these areas. Amounts are forecast to range from less than a tenth of an inch across most of the valley, to around a quarter to half an inch over the northern Sierra. Snow amounts of around 2-5 inches will be possible above about 4-5k ft. Mountain travel delays and chain controls are possible during this weekend system. Travelers should plan accordingly.
Extended Discussion (Monday through Thursday)
Weak troughing over NorCal continues Monday morning which may continue some light precipitation across the mountains, with a upper low noted off the coast of Southern California. This low is expected to progress northeast on Tuesday, before shifting southeast for the ladder half of the week. The heaviest precipitation should be across SoCal, although the southern portion of the Sacramento Valley and mountain areas may see a couple tenths of an inch. Will need to continue to watch the exact track of this low to gain more confidence in rain/snow amounts. A brief period of ridging may follow behind this feature, although unsettled weather looks possible for next weekend.