NWS Area Weather Forecast Discussion
County Warning Area [CWA]: STO Regional NWS Weather Office: Sacramento, CA
FXUS66 KSTO 042246
Area Forecast Discussion
National Weather Service Sacramento CA
246 PM PST Thu Mar 4 2021
Dry and mild weather through tomorrow. Rain and mountain snow
chances return over the weekend and early next week with possible
mountain travel delays.
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
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.
.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
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.
Winter Weather Advisory from 10 PM Friday to 10 AM PST Saturday
for West Slope Northern Sierra Nevada-Western Plumas