February 28, 2019 – Showers mainly over the Northern Sierra today with continued travel impacts. Isolated light mountain showers Friday. Wet weather again over the weekend with Sierra Cascade travel impacts Friday night through early Sunday.
Discussion
A few continuing showers over the northern Sierra this morning as a shortwave trough pivots across this area in upper level southwest flow. The remainder of the forecast area is seeing a break in precipitation this morning under flat high pressure ridging over the southwest U.S. Most of the forecast area will remain dry today through Friday. Exceptions may be over the Sierra where orographics and moisture may combine for a few light showers and over the northern mountains where a low dropping out of the Gulf of Alaska may bring a few light showers. Even with partial clearing over the next couple of days, daytime highs will remain a few to several degrees below normal.
Precipitation spreads back over northern California Friday night as a Pacific low pushes in off the coast. Models in fairly good agreement in pushing a cold frontal band on to the central California coast Friday night and early Saturday morning. Heavier precipitation with this system still appears will be from about Sacramento southward but lighter precipitation still looks likely northward to the northern portions of the forecast area. Snowfall amounts over the northern Sierra look significant and have issued winter storm watch above 6000 feet for heavy snow Friday evening through Sunday morning. Showers drop off on Sunday morning as the main frontal band shifts to the southeast. Most areas will see drop off in precipitation Sunday afternoon but orographics will keep light showers going over the Sierra Cascade range.
Extended Discussion (Monday through Thursday)
Light mountain showers could linger into Monday; otherwise, dry conditions are anticipated ahead of the next Pacific system that is expected to arrive on Tuesday. This Pacific system taps into a weak to moderate AR 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″ across the Valley, and 2-4.5″ over the foothills/mountains through at least Wednesday afternoon. Initially, snow levels could rise to 4500-6000 feet late Tuesday into early Wednesday, then fall to 3000-4000 feet Thursday as cold air filters in. 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. Precipitation could linger into Thursday.