High Wind and Strong Wind in California, January 18 to 20, 2021

Area Forecast Discussion
National Weather Service Sacramento CA
345 AM PST Mon Jan 18 2021

.SYNOPSIS...
Strong gusty north to east winds will continue early this week as
a weather system strengthens to the south of the region. The
strongest winds are expected tonight and Tuesday. Less windy
conditions expected by mid-week, then precipitation chances return
for the end of the week.

&&

.DISCUSSION...
Satellite imagery shows a band of high clouds moving over NorCal
ahead of the initial system dropping south off the coast. North
and east surface pressure gradients have continued to tighten
overnight (MFR-SAC around 15-16 mbs and RNO-SAC around 9-10 mbs).
We're already seeing gusts of 25-35 mph across the northern
Sacramento Valley, gusts of 35-50 mph along the western edge of
the Sacramento Valley, and gusts of 40-50 mph across the northern
Sierra (locally above 60 mph near the mouth of the Feather River
Canyon).

Temperatures remain very mild across windier portions of the area.
Current readings are mostly in the 60s across the northern half of
the Sacramento Valley, while temperatures are in the 40s to the
south where winds are lighter. Some light valley fog will be
possible to the south and east of Sacramento early this morning.

Breezy north winds will continue to spread south through the
Central Valley today. Winds may subside slightly over the
foothills and northern Sierra this afternoon and early evening as
surface pressure gradients relax a bit.

Stronger winds are forecast to develop tonight and Tuesday as the
second portion of the system drops south from the Great Basin
across central California and deepens the developing closed low to
the southwest of SoCal. Increasing upper level support, stronger
subsidence, and strengthening cold-advection will all work drive
strong winds. Widespread gusts over 60 mph will be possible across
the high Sierra, while gusts of 45-55 mph will be common over the
western half of the Central Valley and adjacent foothills. Gusts
over the northern Sierra foothills will be more localized to
ridgetops and near canyons.

For the valley, the strongest winds will likely be along the
western edge of the Sacramento Valley south into the western
Delta. The NAEFS anomaly table still pointing toward a potentially
stronger wind event for areas to the southwest of Sacramento
centered on 18Z Tuesday (return interval between 10 to 30 years).
Power outages and tree damage are certainly not out of the
question.

By Tuesday evening, winds will start to decrease, especially
across the Valley. Gusty winds are expected to linger over the
Sierra Tuesday night, weakening significantly by Wednesday
morning.

Over the course the first half of the week, temperatures will
gradually cool with highs returning the low/mid 60s in the Valley
by Wednesday.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
Ensembles indicate a closed upper low dropping southward along
the West Coast and into NorCal Friday and Saturday. This system
will bring some precipitation to the region, mainly over the
northern and eastern foothills and mountains. Most precipitation
is forecast to be south of I-80 over the Sierra by late Saturday
morning. A few inches of snow are possible at pass levels, leading
to slick roads and mountain travel delays. Dry conditions return
late Saturday into Sunday as the upper low exits the region. Then,
colder and wetter conditions are forecast early next week as
ensembles depict a stronger/colder system that could potentially
bring widespread precipitation.

&&

.AVIATION...
VFR conditions next 24 hours with the exception being some MVFR
visbys possible from KSMF southward through about 16Z-18Z today.
North wind gusts up to 30-40 kts in the Central Valley and Delta,
locally higher. Areas of northeast to east wind gusts stronger
than 50 kts over the Sierra.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 7 PM PST Tuesday for Northeast
Foothills/Sacramento Valley-Shasta Lake Area / Northern Shasta
County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

Wind Advisory until 7 PM PST Tuesday for Carquinez Strait and
Delta-Central Sacramento Valley-Motherlode-Mountains
Southwestern Shasta County to Western Colusa County-Northern
Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&