March 1, 2019 – Isolated light mountain showers today. More significant precipitation over the weekend with Sierra Cascade travel impacts from snow Friday night through early Sunday. Mainly dry Monday then another round of precipitation late Tuesday through mid week. Significant mountain travel impacts and valley flooding possible.
Discussion
Moist westerly flow over the state combined with orographics bringing a few light showers to the northern Sierra this morning. The remainder of the forecast area is seeing dry but cloudy conditions. An upper low dropping southward off the Oregon coast may bring a few light showers to the northern mountains later today but significant impacts are not expected. A Pacific low pressure system currently centered near 140 west 30 north will push towards the coast today.
Models are fairly consistent in spreading light precipitation across the north state ahead of this system this evening with the main cold frontal band pushing in to central California early Saturday morning. The heaviest precipitation moves across the central part of the state Saturday morning. Models still keep heaviest precipitation from about interstate 80 southward with lighter precipitation farther south. Snow levels with this system remain moderately high but still well below pass levels so mountain travel impacts are likely. Have upgraded winter storm watch to a warning over the northern Sierra with just a winter weather advisory farther north where precipitation amounts are expected to be lighter.
Frontal band shifts quickly to the southeast Saturday afternoon and evening with precipitation turning to showers overnight. Showers continue into Sunday as moist westerly flow continues over the state. Most of the forecast area will see drying on Monday as a ridge builds temporarily over the western U.S. pushing precipitation threat north and east during the day.
Extended Discussion (Tuesday through Friday)
An active weather pattern is expected through the extended period as a strong Pacific system begins to impact the region by Tuesday afternoon. This system will have a weak to moderate AR associated with it as indicated by the West Coast AR Landfall Tool. Thus, moderate to heavy precipitation is expected across interior NorCal with the bulk of storm impacts expected Tuesday evening into Wednesday. Preliminary QPF amounts indicate 1-2.5″ across the Valley, and 2-5″, locally higher, over the foothills/mountains through Thursday afternoon. Initially, snow levels could rise to 4500-6000 feet Tuesday into Wednesday, then fall to 3000-4000 feet Thursday. Once again we should see a resurgence of travel impacts due to mountain snow and hydro issues due to small stream/river and urban flooding. Lingering precipitation late next week, but lighter precipitation amounts are anticipated.