Winter Storm Warning 2, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
345 AM PST Fri Jan 6 2023

.SYNOPSIS...
A series of strong storms will move across the region into next
week bringing moderate to heavy rain, high elevation snow, and
gusty winds. Periods of heavy precipitation will keep flooding
threats elevated and mountain travel impacts at the forefront.

&&

.Discussion...
Short-wave ridge moving in has brought a break in precipitation to
much of the forecast area overnight, though light precipitation
associated with the approaching warm front is beginning to spread
back inland across areas mainly to the north of Interstate 80. The
next frontal system will begin to move into northwest California
this afternoon bringing an increase in QPF to the Coast Range and
Shasta County mountains where some areas could see around an inch
of QPF by sunset. This front will slow tonight and early Saturday
as the parent short-wave lifts north, but widespread light to
moderate precipitation will only gradually spread south.

Another short wave trough will be right on the heels of
Saturday's. Warm air advection precip develops ahead of it later
Saturday with another cold front moving through Sunday. Both of
these systems will have plenty of moisture to work with and
periods of moderate to heavy rain can be expected. 1' to 2" over
the Valley, 1-3" over the foothills, and 2-5" over the mountains
(especially the Shasta Co mountains and Feather basin where
southerly orographic enhancement will be maximized. Snow levels
with the weekend systems will be 4500-5500 feet with the majority
of the snow accumulation above 5000 feet. Snow totals are looking
to be 1-2 feet with some of the higher elevations seeing 3 feet or
more leading to significant travel impacts.

We will also see increased southerly winds over the weekend with
wind gusts 30-45 mph over the Valley and up to 55 mph over the
mountains as each front moves through, though winds will likely be
less than the last couple of systems.

The rainfall over the weekend will bring renewed rises to local
streams, creeks, and rivers.

We're still looking at Monday as the beginning of another
potentially "big, or bigger" event as a stronger system moves
ashore bringing widespread moderate to heavy rain and strong
southerly winds. Snow levels will rise to near the higher pass
levels, but travel will likely remain dicey with strong winds,
lots of slush with a mix of rain and snow at the pass levels. This
will be a longer duration strong AR system, and the trajectory
will be more favorable for very heavy rain in the foothills and
northern Sierra from orographic enhancement.

Flood impacts will likely become more widespread Monday as the
cumulative effects from all the recent rain come together. Pay
close attention to the weather and have a plan if you live in or
near a flood prone area.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Moderate to heavy rain from Monday's AR will likely be continuing
during the day on Tuesday as a strong negative-tilt upper trough
swings in bringing the potential for bands of heavy showers and
embedded thunderstorms to put a finishing touch on early week
precipitation. GEFS plume averages for QPF for Sacramento are
about 2 inches for the 36 hour period from early Monday through
Tuesday afternoon, though there's a large number of members that
are up around 3-4 inches for that period. Modesto's numbers look
pretty similar. Up at Redding, the average is about the same at 2
inches, but the higher end numbers are around 4 inches or more.
Given the strength of the AR, the official forecast is tracking
toward these higher end numbers.

Other than Monday, Tuesday is probably the day where you'll
likely need to keep a really close eye on the weather as the
potential for widespread flooding of rivers, creeks, streams and
roadway and urban flooding will be at its highest during the next
week as all the runoff and heavy precipitation comes together
resulting in a mess. Winter weather impacts will also be
increasing in the Sierra on Tuesday as snow levels lower and heavy
precipitation continues.

We may see a brief break during the middle of next week before
additional rain arrives late next week.

&&

.AVIATION...
VFR conditions at the TAF sites with local MVFR cigs through 12z
Friday. IFR/LIFR over the mountains through 12z Friday due to
snow. BKN to OVC skies 035-050 Friday with light showers possible
after 12z for the northern terminals. Southerly winds up to 12
knots.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from late Saturday night through Wednesday afternoon
for Carquinez Strait and Delta-Central Sacramento Valley-
Motherlode-Mountains Southwestern Shasta County to Western
Colusa County-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area /
Northern Shasta County-Southern Sacramento Valley.

Winter Storm Warning until 4 AM PST early this morning for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

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