146
FXUS66 KSTO 222131
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
131 PM PST Sun Dec 22 2024

.SYNOPSIS...
Periodic chances for precipitation and breezy to gusty southerly
winds are expected to continue into the week ahead as a series of
weather systems impacts the region.

.DISCUSSION...
Current GOES-West satellite imagery shows a fairly robust swath
of low level cloud cover and mid to high level clouds streaming
toward interior NorCal this afternoon. While resultant radar
imagery generally depicts a lack of attendant precipitation at
this time, some returns are beginning to pop up across Shasta and
Tehama counties as the next wave of precipitation approaches.
Prior to that though, some patchy fog development will be possible
ahead of the precipitation this evening. Additional fog
development, likely more dense than the evening fog, is then
expected into Monday morning following the burst of evening and
overnight precipitation.

The progressive nature of this wave alongside snow levels
generally above 7000 feet are expected to limit overall impacts
from precipitation. Current forecast precipitation totals through
Monday morning sit around 0.25 to 0.5 inches across the Valley and
foothills, with 0.5 to 1.5 inches possible along the
Sierra/southern Cascades. Given high snow levels, most
accumulating snowfall is expected above pass level with this wave.
A slightly more pronounced lull between waves is then expected
for much of Monday, before precipitation chances begin to increase
again from north to south late Monday into Tuesday.

The next wave is expected to be stronger, colder, and wetter than
previous waves over the weekend, with a more defined southerly
track expected with this system. As a result, higher precipitation
totals look to accompany rapidly falling snow levels on Tuesday,
which will likely introduce some holiday travel impacts to the
region throughout Tuesday. Additionally, breezy to gusty southerly
winds (Low elevations: 20 to 30 mph and Along the Sierra: 40 to
50 mph) and isolated thunderstorm potential (10% to 20%) are
anticipated as the system moves in as well. Current probabilities
of exceeding 0.5 inches of liquid precipitation are around 60% to
90% for much of the Delta, Valley, and lower foothills, with 70%
to 95% probabilities of exceeding 1 inch across the
Sierra/southern Cascades and northern Sacramento Valley and
surrounding terrain. Snow levels are expected to rapidly decrease
into Tuesday, sitting near 6000 to 7000 feet on Tuesday morning,
before falling to 5000 to 6000 feet by Tuesday afternoon. As a
result, the majority of accumulating snowfall is expected above
6000 feet, with generally 60% to 90% probabilities of exceeding 6
inches of snowfall through Tuesday evening.

As quickly as this more potent wave arrives, precipitation
chances are expected to rapidly drop off Tuesday night, with
overall dry conditions anticipated for much of Wednesday
(Christmas Day). With a drier period expected to follow,
additional chances for fog development will likely be possible,
but there is currently some uncertainty with respect to that at
the moment. Otherwise, near normal temperatures and light winds
are primarily expected for the holiday.

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


.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
Persistently active weather is expected to continue through at
least the end of the week, with latest ensemble trends indicating
a continuation of periodic precipitation chances into next
weekend. Overall uncertainty does notably increase through the
weekend, with ridging aloft attempting to build in from the south,
but ensembles differ on how this and additional shortwave
ejections will interact late in the extended forecast period.
While the Thursday into Friday wave of precipitation looks to
follow a similar trajectory to the Tuesday system, ensemble
guidance currently indicates a slightly weaker synoptic look to
it. As a result, probabilities of liquid precipitation exceeding
0.5 inches around 40% to 60% favor the Delta and southern
Sacramento and northern San Joaquin Valleys, while probabilities
of exceeding 1 inch around 60% to 90% favor the northern
Sacramento Valley and surrounding terrain and northern
Sierra/southern Cascades from Interstate 80 northward. Initial
snow levels around 4500 to 5500 feet late Wednesday/early Thursday
do look to increase closer to 5500 to 6500 feet from midday
Thursday into Friday. Resultant probabilities of snowfall
exceeding 6 inches above 6000 feet through Friday evening sit
around 40% to 70% at this time.

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

&&

.AVIATION...
MVFR/IFR/LIFR in low cigs through 00z, with precipitation chances
increasing from north to south between 00z and 09z. Snow levels
remain 6500-7500 feet. Additional visibility reductions in BR/FG
then anticipated following precipitation, generally after 09z.
Light southerly winds less than 12 kts expected next 24 hours,
although some gusts to 30 kts possible along Sierra crest through
12z.

&&

.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.

&&

$$