March 21, 2019 – Scattered mountain showers today with light snow higher elevations. Another round of rain and snow Friday afternoon through Saturday with enough mountain snow for travel impacts. Dry Sunday then more rain and mountain snow early next week.
Discussion
Negative tilt upper trough over the state this morning brought a few light showers to the northern Sacramento valley earlier this evening as well as some light shower activity over the northern Sierra. Most showers have ended but a slight threat of mountain showers will continue today as the upper low shifts eastward into the the Great Basin.
Daytime highs will reach near normal today in the central valley under mainly sunny skies while the mountains remain mostly cloudy. Most areas will see dry conditions tonight under brief upper level ridging before the next Pacific frontal system pushes onshore Friday morning.
By mid day Friday, areas west of the Sacramento valley should be seeing light precipitation if current model projections hold. By Friday afternoon, the frontal band shifts inland over NorCal with precipitation expected over the Sierra Cascade range.
Travel impacts are likely over the Sierra during the Friday to Saturday afternoon timeframe as the moderately cold for the season storm system will likely bring several increases of snowfall below pass levels. Have therefore issued a winter weather advisory to deal with likely travel difficulties.
Light precipitation at the lower elevations will likely only bring minimal issues. The main upper trough is forecast to move through Saturday afternoon and night for continued shower activity over the Sierra Cascade range. Snow levels at this time are forecast to drop to 4000 feet before precipitation drops off Saturday night.
Upper ridging will make Sunday a fairly dry day with mainly fair skies warming daytime highs to near or a little above normal. This dry period should make Sunday a fairly good travel day. This break will be fairly brief, however, with the next Pacific system pushing inland by Sunday night.
Extended Discussion (Monday through Thursday)
An unsettled and cool pattern is expected next week, with periods of rain, mountain snow and breezy winds.
Confidence is good that wet weather will spread across the area Monday, with general agreement across GEFS ensemble members and the potential for a weak atmospheric river continues. Models are pretty consistent in directing the best moisture over Northern California, but there is some variance in exactly where.
Additional waves with decent moisture plumes are expected to continue through the week, bringing periods of moderate to heavy rain, but exact timing remains uncertain. Early estimates of precipitation are around 1 to 4 inches for Monday through Wednesday. Snow levels continue to range between around 5000 to 6000 feet, with the potential for travel delays.