Winter Storm Warning 1, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
440 AM PST Fri Jan 4 2019

.SYNOPSIS...
Dry today, then wet weather returns this weekend. Periods of
hazardous mountain travel possible Saturday through middle of next
week due to heavy snow and gusty wind. gusty winds in the central
valley and foothills Saturday.

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.DISCUSSION...
Upper ridge axis has now shifted into the Great Basin. This has
allowed a great deal of high cloud cover to spill over the ridge
and into northern California. Clearer skies from about
Oroville south has allowed some light fog to form in the central
valley but so far nothing too dense. An offshore Pacific frontal
band will approach the coast today but the daytime hours should
remain dry under high cloud cover. Not expecting much change in
high temperatures today even with high cloud cover due to warm air
advection ahead of the front. Current timing moves offshore front
on to the norcal coast by 12z Saturday with models sweeping it
across the state during the day. Timing has been quite consistent
but precip amounts have not with GFS remaining consistently wetter
than the ECMWF. Either way, with snow levels below major pass
levels, mountain travel issues a high likelihood with several
inches to 2 feet or more of snow expected at the higher
elevations. In addition to the valley rain and mountain snow,
strong south winds are expected ahead of the front on Saturday.
Surface Gradients from MFR to SAC are forecast by the GFS to top
12 mb with 925 mb winds Saturday afternoon indicating 40 knots or
higher. Have issued wind advisory for much of the central valley
and interior coast range from 15z Sat through 03Z Sunday when
pressure gradients should relax behind the front. Showers continue
Saturday night through Sunday as upper through swings across the
region.

Next frontal system pushes through quickly on the heels of the
first bringing another round of steady precipitation into the
north state as early as Sunday afternoon. Combination of
relatively low snow levels and precipitation amounts will bring
more mountain travel impacts Sunday night into Monday so more
winter weather hazard products will likely be needed for this time
period. Another round of increased wind is expected Sunday
afternoon through Monday but at this time, this wind event does
not look as strong as on Saturday.

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

A cold front will approach the area on Tuesday with lingering
showers expected during the morning hours for communities north
of I-80. The frontal system is expected to make it to the north
Coast late in the evening and arriving into our CWA early
Wednesday morning. Models continue to struggle with the exact
timing and strength with this system, but valley rain, mountain
snow, and gusty winds are to be expected with this system. They do
have some similarities though for Thursday with both keeping
lingering moisture around the area and building a ridge on
Friday.

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.AVIATION...

Little change to the forecast as primarily VFR conditions are
expected for the next 24 hours. Pockets of MVFR and IFR conditions
are expected through the morning hours, primarily around KSMF and
southwards.

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Saturday morning through Sunday morning
for Clear Lake/Southern Lake County-Mountains Southwestern
Shasta County to Northern Lake County-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.

Wind Advisory from 7 AM to 7 PM PST Saturday for Carquinez
Strait and Delta-Central Sacramento Valley-Clear Lake/Southern
Lake County-Motherlode-Mountains Southwestern Shasta County to
Northern Lake County-Northeast Foothills/Sacramento Valley-
Northern Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

Winter Storm Watch from late tonight through Sunday morning for
Shasta Lake Area / Northern Shasta County.

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