Winter Storm in California, March 4 to 5, 2022

Area Forecast Discussion
National Weather Service Sacramento CA
1251 PM PST Thu Mar 3 2022

.SYNOPSIS...
Periods of showers and mountain snow expected today into
Saturday. Expect hazardous mountain travel Friday afternoon into
mid-day Saturday. Slight chance for thunderstorms across portions
of the Valley and Sierra foothills Friday afternoon. Dry
conditions, cool nights, and warm afternoons return next week.

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.DISCUSSION...
Northern California radars have been flipped into precipitation
mode as prefrontal / warm-sector showers have managed to develop
along the western side of the Sacramento Valley. Radar
reflectivity looks a bit more impressive than reality; ground-
truth rain observations reveal only a few/several hundredths
along/west of Interstate 5 with an isolated tenth or so. Upper-
level trough located offshore will gradually approach the coast
over the next 12-24 hours. As it approaches, the base of the
trough will split with the vort max pushing onshore farther south
than what was previously anticipated a few days ago -- near Point
Conception in Santa Barbara County. This trajectory will prevent
widespread precipitation across interior NorCal; the best chance
for light precipitation will generally remain along/west of
California Highway 99 through today.

Another wave will drop south from the British Columbia Coast on
Friday and Friday night. This wave's trajectory will provide a
much better chance of precipitation for a solid portion of
northern California, including impactful snowfall to the Sierra.
Snow levels will initially start on Friday around 6000 to 7000
ft, and then lower through the day to around 4500 to 5500 ft later
in the afternoon, and eventually as low as 1500 to 2500 ft after
midnight and into Saturday morning. Snow accumulations above 4000
ft elevation will range from 4 to 8 inches (locally around a foot
at the peaks), 1 to 4 inches in the upper foothills, and even a
dusting as low as 1500 ft. Motorists with weekend travel plans to
the mountains should plan accordingly for winter weather impacts,
especially those that leave after 12 pm on Friday. As always,
check with Caltrans for the latest road conditions and
restrictions.

Valley precipitation chances are expected to remain on the light
side tomorrow. Unfortunately, some locations may completely miss
out on any precipitation whatsoever. The showery/convective-
nature will make precipitation hit/miss as the best instability
will be in the foothills and eastern portions of the Valley. That
said, these showers and even a few isolated thunderstorms will
have the potential to bring locally brief downpours as well as
small hail. According to the latest National Blend of Models, the
24-hour probability of exceeding 0.01" (measurable rain) in
Sacramento is between 40-50% for Friday.

Scattered mountain snow showers may linger into Saturday afternoon
along/south of US-50. Sunday will start off cool with Valley lows
dropping to the middle 30s, and then rebound nicely for the
afternoon to the middle 60s. // Rowe

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.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
The workweek will start out with a ridge to the west and
departing trough to the east, resulting in northerly flow overhead
NorCal. Weak wave will drop south on Monday that will result in
some north/east winds, but nothing impactful based on current
guidance. Temperatures will gradually warm to the upper 60s/low
70s by the middle of next week. Overnight lows will remain a the
cool side with the dry air mass. Clusters/ensembles in the 8-10
day range point to more ridging in the eastern Pacific with dry
conditions for us in NorCal. Climate Prediction Center's 8-14 day
outlook similarly favors below normal precipitation most of the
Golden State. // Rowe

&&

.AVIATION...
A weather system continues to produce thick cloud cover and light
rain or showers to areas north of the Sacramento region. Showers
are expected to dissipate by tonight but will return Friday
afternoon as another weather system will bring isolated showers
over the Valley and heavier snow over the Sierra. Mostly VFR
conditions are expected with local MVFR in snow or rain showers.
Surface winds forecast to remain less than 12 kts, increasing
after 18z Friday to 15-20 kts with gusts up to 25 kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon Friday to 1 PM PST Saturday
for Burney Basin / Eastern Shasta County-Motherlode-Northeast
Foothills/Sacramento Valley-Shasta Lake Area / Northern Shasta
County-West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

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