Winter Storm and Hail in California, March 4 to 7, 2023

Area Forecast Discussion
National Weather Service Sacramento CA
350 AM PST Sat Mar 4 2023

.SYNOPSIS...
Another strong winter storm will bring multiple feet of snow with
major impacts expected once again over the foothills and
mountains Saturday into early next week.

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.Discussion...
Building upper ridging into Alaska will help stall upper level low
pressure off the Pac NW coast today through the middle of next
week with multiple waves of mid-level vorticity rounding this gyre
and pushing into northern CA with the first shortwave trough axis
crossing the far northern CA coast this morning. At the same
time, a pronounced and intensifying Pacific jet streak, progged to
reach 150+kt by tonight, will overlap with the mid-level
confluence to surge moisture across northern/central CA. The
overlap of height falls, PVA, and left jet exit diffluence along
the upper jet will provide widespread deep layer synoptic lift to
support rounds of moderate to heavy snowfall over the Sierra
through Sunday night before rates decrease with the very occluded
system.

Snow levels will rise up to 3000 ft today over the Sierra ahead
of this first wave, but then lower this evening following cold
front passage after 5pm, remaining below 2000ft through the event
with significant snow down to many foothill communities. 2 to 5
feet of snow are forecast over much of the Sierra Nevada through
Sunday night with 5 to 20 inches down into the foothills. During
the heaviest snow, rates may approach as high as 2 to 3 inches per
hour. Southerly winds will increase tomorrow and be gusty through
the afternoon and overnight into early Sunday. Mountain and foothill
travel will become extraordinarily difficult to impossible with
extended delays and closures highly probable. Conditions will
deteriorate after midnight tonight. Always check with Caltrans for
the latest road conditions, restrictions, and closure information.
And remember: NEVER drive beyond any road closed signs/barriers.

Total rainfall is only expected to bring minor impacts such as
slick roadways and ponding of water in low-lying areas. There is
around a 10 to 20 percent chance of afternoon thunderstorms today
and Sunday afternoons, which may produce briefly heavy rainfall,
small hail, and gusty/erratic winds. Total rainfall will generally
range between 0.5 to 1.25 inches.

The very stalled pattern and focus of the Pacific jet farther
east allows the heavier snow over the Sierra Nevada to become much
more intermittent Monday/Tuesday, but the onshore flow does last
through midweek which will likely hinder efforts to help Sierra
Nevada communities buried in recent snows, as several inches of
snow are possible each day.

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.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Ensembles and clusters keep a large scale upper level trough over
the West Coast States through the end of the week. This will
maintain cool and unsettled weather conditions over NorCal through
the week. Weak disturbances rotating through the trough will
provide periods of light snow through Friday. Relatively low snow
levels will bring snow down into the upper foothills at times.
Current forecast snow amounts would suggest 2 to 3 inch per day
rates, which could bring 4 day totals to near a foot in some
areas. Temperatures will be about 10 degrees below normal with
highs in the 50's and lows in the 30's at Valley
locations.Uncertainty increases in the Friday/Saturday timeframe,
as ensembles deviate drastically on strength and timing of
potential system next weekend.

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.AVIATION...
Showers spread inland from northwest to southeast today bringing
local MVFR conditions. Gusty winds through the early evening,
with southerly gusts up to 20-35 kts in the Valley and south to
southwest gusts in the mountains up to 40-50 kts. Thunderstorms
possible after 18Z.

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 10 AM PST Monday for Mountains
Southwestern Shasta County to Western Colusa County-Shasta Lake
Area / Northern Shasta County.

Winter Storm Warning from 10 AM this morning to 10 AM PST Monday
for Burney Basin / Eastern Shasta County-Motherlode-Northeast
Foothills/Sacramento Valley-West Slope Northern Sierra Nevada-
Western Plumas County/Lassen Park.

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