Flash Flood Warning 9, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
203 PM PST Mon Dec 23 2024

.SYNOPSIS...
Periodic chances for moderate precipitation and breezy to gusty
southerly winds are expected to continue through the weekend as a
series of weather systems impacts the region. Isolated
thunderstorms possible on Tuesday.

.DISCUSSION...
Cloudy skies continue to blanket much of interior Northern
California as light showers ahead of the next system start to
shimmy over the Coastal Range. This next system, which arrives
later tonight and lasts into Tuesday, is expected to be stronger
and colder than previous weekend systems. Current probabilities
of exceeding 1 inch of liquid precipitation are around 70-100%
across the northern Sacramento Valley, foothills and mountains.

Forecast precipitation totals sit around 0.25-1" across the
Valley, with 1-2.5 inches possible along the Sierra/southern
Cascades and foothills. Snow levels will start above pass levels,
but rapidly lower to around 5000-6500 feet by Tuesday morning.
NBM advertises a 60-90% probability of exceeding 6 inches of
snowfall through Tuesday evening. Moderate mountain snow is
expected, with snowfall rates up to 1-2.5" per hour possible
Tuesday morning. A Winter Weather Advisory remains in effect for
the southern Cascades and northern Sierra for elevations above
6000 feet from 7 AM to 7 PM Tuesday. Total snow accumulations of 5
to 10 inches are forecast above 6000 feet; locally higher amounts
over peaks.

Additionally, NBM depicts a 10-20% probability of thunderstorm
development on Tuesday. Isolated thunderstorms will be possible
along the main frontal band as it passes through early tomorrow
morning, and also behind the front with some possible clearing
late morning into the early evening. Gusty southerly winds are
also anticipated late Monday night through Tuesday morning as the
system moves through, with gusts up to 25-35 mph over the northern
Sacramento Valley and northeast foothills; stronger gusts over
the Sierra. Precipitation chances are expected to taper off
Tuesday night, with overall dry conditions anticipated for much of
Wednesday (Christmas Day) as short-lived ridging moves overhead.
With a drier period expected to follow, additional chances for fog
development will likely be possible (10-20% probability of
visibilities less than 1 mile).

Ensembles indicate an active pattern continuing through the
weekend. The next wave is expected to arrive late Wednesday night
or early Thursday, bringing another round of widespread
Valley/foothill rain and mountain travel impacts. Snow levels will
start around 4500 to 5500 feet early Thursday, then increase to
around 5500-6000 feet by Thursday afternoon. Moderate snow is
possible, with probabilities of snowfall exceeding 6 inches above
6000 feet ranging from 40% to 70% through Thursday night. Breezy
southerly winds will accompany the system.

Please continue to check weather.gov/sto for the latest updates
and check quickmap.dot.ca.gov before you go this holiday season!

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
While uncertainty remains, ensembles suggest an active pattern
persisting late week into the weekend as additional waves move
across the area. Probabilities of liquid precipitation exceeding
0.5 inches range from 40% to 60% across the Delta and southern
Sacramento through Sunday night, while probabilities of exceeding
1 inch around 60% to 95% favor the northern Sacramento Valley,
foothills and mountains. Probabilities of snowfall exceeding 6
inches above 6000 feet through Friday evening sit around 20% to
50% at this time, with minor to moderate mountain travel impacts.
Snow levels start around 6000 feet Friday morning, then rise above
pass levels by Saturday. Drier conditions may return by early
next week.

Please continue to check weather.gov/sto for the latest updates
and check quickmap.dot.ca.gov before you go this holiday season!

&&

.AVIATION...

MVFR/IFR with localized LIFR conditions from low ceilings and
scattered showers north of I-80 this afternoon. Valley and
mountains from 00z Tue through 12z Tue as light to moderate
precip. develops. Light southerly winds less than 12 kts expected
until 00z Tue, then 15-30kt gusts through the Valley with 35-45
kts along the Sierra crest after 09z Tues. Snow levels around
6500-7500 feet, becoming 8000-9000 feet after 00z Tue. Snow levels
then drop to 5000-6000 feet after 18Z Tuesday. Isolated
thunderstorms will also be possible between 12z Tuesday through
00Z Wednesday for much of the Valley, foothills, and Sierra.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 7 AM to 7 PM PST Tuesday for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&