O'Brien, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

012
FXUS66 KSTO 212129
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
129 PM PST Sat Dec 21 2024

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

.DISCUSSION...
As of early this afternoon, current radar imagery depicts a
narrow band of precipitation beginning to exit interior NorCal.
While light to locally moderate precipitation will be possible
along this line, cloudy, but dry conditions are prevailing behind
it. Despite the seemingly tapering nature of precipitation, an
additional plume of atmospheric river moisture looks to spread
eastward late tonight into Sunday. With nonzero forcing remaining
in place during this time, a re-intensifying band of precipitation
will be possible from Interstate 80 southward later today.
Highest additional precipitation totals of 0.5 to 1.5 inches are
expected across the foothills and along the Sierra, with only 0.1
to 0.25 inches anticipated at lower elevations through midday
Sunday. Elsewhere outside of precipitation, some morning fog
development will be possible into Sunday morning as well.

A very brief lull in precipitation is then expected from late
Sunday morning into the afternoon hours. This looks to be a very
short lived reprieve as the next shortwave ejection in the series
is primed to occur Sunday evening into midday Monday. As this
shortwave is expected to follow a similar, progressive trajectory
to prior systems, light to moderate precipitation is anticipated
late Sunday into Monday morning, gradually tapering off into
Monday. Some higher elevation mountain locations may squeeze out
precipitation totals up to 1 inch, but generally 0.1 to 0.5 inches
of precipitation are expected through midday Monday with this
wave. Snow levels are still expected to remain above 6500 feet,
with snowfall accumulations remaining above pass level.

A slightly more pronounced lull between systems is then
anticipated beginning Monday morning, but the next wave in the
series will begin to introduce increasing precipitation potential
from north to south by Monday evening. Current ensemble trends
indicate a stronger trough digging further southward with the late
Monday into Tuesday system. As a result, gustier southerly winds
are anticipated along with periods of moderate to locally heavy
precipitation and some isolated thunderstorm potential as well. At
this time, winds are expected to increase overnight and peak
through Tuesday morning, with gusts 20 to 30 mph across the Delta,
Valley, and foothills while some gusts up to 45 mph will be
possible along the Sierra.

Forecast precipitation for this early week system remains largely
unchanged, with generally 0.75 to 1.5 inches possible across the
Delta, southern/central Sacramento Valley, and northern San
Joaquin Valley, with 1 to 3 inches possible across the northern
Sacramento Valley and surrounding terrain and along the
Sierra/southern Cascades. Snow levels are expected to fall through
Tuesday as the system progresses across the region, beginning
around 8000 feet Monday evening before dropping to near 5000 feet
by Tuesday afternoon. Resultant probabilities of snowfall
accumulations exceeding 8 inches above 6500 feet from Interstate
80 southward sit around 70% to 90% at this time, with 15% to 30%
probabilities down to 6000 feet.


.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
By Wednesday (Christmas Day), mostly dry conditions are expected
to briefly return as a break between systems occurs. Light to
breezy winds are expected for the holiday with high temperatures
near late December normals, low to mid 50s across the Delta,
Valley, and foothills and 40s to low 50s at higher elevations.
There are still some ensemble discrepancies regarding the timing
of additional weather systems late week into the following
weekend, but precipitation chances are expected to increase by
Thursday, with some guidance indicating the return of
precipitation by Wednesday evening. Regardless, ensemble guidance
is in good agreement on additional precipitation Thursday into
Friday, with further uncertainty within the upper level pattern by
next weekend. While precipitation totals will likely fluctuate,
current probabilities of liquid precipitation greater than 1 inch
sit around 15% to 35% from Interstate 80 southward, with more
notable 70% to 95% probabilities for most locations north of
Interstate 80 at this time. Forecast snowfall accumulations will
vary as well, but snow levels around 5000 to 6000 feet are
anticipated, with most forecast accumulating snowfall expected
above 6000 feet at this time. Additional breezy to gusty southerly
winds will be possible with the late week weather system
progressions, but magnitude of the winds will be tied to the track
of these subsequent waves.

&&

.AVIATION...
MVFR/IFR in isolated to scattered showers expected next 24 hours
across interior NorCal, with MVFR/IFR/LIFR cigs outside of
precipitation and areas of BR/FG possible after 06z. Breezy
southerly winds today become light and variable after 00z. Lower
elevation surface winds expected to remain less than 12 kts, with
some gusts to 40 kts possible along the Sierra crest through 06z.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$