Area Forecast Discussion
Issued by NWS Sacramento, CA

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000 FXUS66 KSTO 042246 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 246 PM PST Thu Mar 4 2021 .SYNOPSIS... Dry and mild weather through tomorrow. Rain and mountain snow chances return over the weekend and early next week with possible mountain travel delays. && .DISCUSSION... We are seeing quiet conditions this afternoon as we sit under a short wave ridge. This ridge will push to the east tomorrow and amplify over the northern Rockies as a trough digs out of the Gulf of Alaska and approaches the west coast. This will bring increased onshore flow starting during the afternoon tomorrow and the breezy southerly winds will continue into Friday night. Wind gusts up to 35 mph will be possible over the Sacramento Valley and over the Sierra with locally stronger gusts as you approach the central Sierra. The bigger impact will be the precip that the trough brings. Showers will begin to move into the Coastal Range around 4pm/0z and will continue to overspread the region during the evening. Widespread rain and snow is expected overnight Friday into early Saturday morning as the trough axis and associated cold front push through the area. We do see some very weak CAPE build in over the area in the lowest levels late Friday night into Saturday morning. There will not be enough CAPE for any thunderstorms and that is a zero concern at this time but should be enough CAPE to bring some enhanced snowfall over the Sierra. Snow rates could be greater than 2"/hr. for a short time between 4am/12z and 7am/15z. We will also see snow levels fall quickly after 1am/9z to 4am/12z as they go from 5000-6000 feet down to 3000 to 4000 feet. Snow totals are looking to be 3-8" above 5000 feet with a dusting to 4" between 3500 and 5000 feet. These snow totals are marginal for a Winter Weather Advisory but given the high snow rates for a time and that it is a Friday night into a Saturday morning went ahead and issued a WSW from 10pm/6z to 10am/18z Saturday. Rain totals are looking to be between a 0.10-0.75" in the Valley with the lowest totals over the San Joaquin and 0.25-1.0" in the Foothills. Trough will weaken, as it moves east into Nevada Saturday with precipitation diminishing during the afternoon. Broad southwest flow over the area with dry weather Sunday before a series of systems impact the area next week. Valley temperatures will be a bit cooler with highs from the upper 50`s to low 60`s. -CJM && .EXTENDED DISCUSSION (Monday THROUGH Thursday)... Potentially active early-middle part of next week as forecast guidance continues to advertise periods of rain and mountain snow for Northern California. Ensembles have an upper level low dropping southeastward from the Gulf of Alaska toward the California coast from Monday to Wednesday. During this time, multiple shortwaves will ripple through the cyclonic flow, the first occurring around late Monday, and another around Wednesday. European ENS mean 1000-500 mb thickness drops to around 530 decameters, which could conceivably drop snow levels to 3000 ft (or less). Main impacts will be the potential for travel delays in the mountains, as well as slick roadways. In terms of snow amounts, the National Blend of Models presently gives Blue Canyon about a 50 percent shot at getting a foot or more of snow from late Monday through Wednesday. Will continue to keep a close eye on this system. // Rowe && .AVIATION... General VFR expected over the next 24 hrs. Surface wind gusts generally under 12 kts. Hi-res models suggest the possibility of the marine layer surging in again; however, confidence is low in a stratus deck forming. If it does, it should stay within the Delta region. Tomorrow, winds will be breezier and mostly from the south with gusts between 20-30kt for the Sacramento Valley. The San Joaquin Valley winds will have a more north and westerly component and be lighter. && .STO WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 10 PM Friday to 10 AM PST Saturday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.