Pollock Pines, California 7 Day Weather Forecast

Wx Discussion - Wx Hazards - Wx Special Statements

Weather Forecast Discussion

045
FXUS66 KSTO 242111
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
111 PM PST Tue Dec 24 2024

.SYNOPSIS...
Precipitation chances gradually decrease into this evening, with
generally dry weather expected for Christmas Day. Precipitation
chances then return late Wednesday night as the unsettled weather
pattern persists into the weekend.

.DISCUSSION...
As of early this afternoon, the majority of widespread
precipitation is confined to the Sierra and adjacent foothills
locations, with an area of clearing skies working into the Valley.
Despite the clearing skies, a progressive plume of moisture
streaming toward the coast range will provide some potential for
isolated to scattered showers across the Valley through the
afternoon. There is some uncertainty with respect to how much
surface heating ahead of this moisture plume will impact
instability, but an uptick to a few hundred J/kg will be possible
over the next few hours, which may be enough to spur some rumbles
of thunder across interior NorCal. Severe potential is expected to
be severely limited by short duration surface heating and
generally weak wind shear, but brief heavy rainfall, gusty winds,
and small hail will be possible with any thunderstorms that do
develop.

While precipitation along the Sierra is gradually exiting the
region this afternoon, any trailing showers/thunderstorms that
develop within the Valley may provide an additional period of
mountain travel impacts into the early evening. Otherwise, snow
levels around 5500 feet this afternoon are expected to gradually
fall to near 5000 feet by this evening, with additional snowfall
accumulations of 3 to 6 inches possible above 6000 feet and
generally a trace to an inch down to 5000 feet. As a result, the
Winter Weather Advisory currently in effect for the
Sierra/southern Cascades above 6000 feet continues until 7 pm
tonight.

As soon as this system ejects eastward, a period of transient
ridging aloft looks to build in across California late tonight
into Christmas Day. This will provide another relative lull in
active weather for much of the holiday, although this brief
stagnation may result in additional fog development by Wednesday
morning. Current HREF probabilities of visibility less than 0.5
miles are around 40% to 60% for Delta, Valley, and foothills
locations generally from Marysville southward. Despite the
potential for a foggy morning to transition into a mostly cloudy
afternoon, seasonable high temperatures are expected across
interior NorCal for Christmas Day.

The aforementioned transient ridge looks to quickly be replaced
by progressive northwesterly flow aloft, which will allow for
additional shortwave ejections and attendant precipitation chances
through the end of the week and into the weekend. As a result, a
rapid return to active weather then begins to creep back in, with
precipitation chances increasing from north to south Wednesday
evening into Thursday. The initial shortwave late Wednesday into
Thursday looks slightly weaker but is expected to follow a further
southward trajectory, while the Friday shortwave ejection
features a deeper trough, but following the flow pattern further
northward. While these systems individually may be lower impact,
with little break, if any, anticipated between these systems,
cumulative impacts will likely nudge higher.

Areal extent of rainfall will generally be tied to the track of
the individual waves, but for the Thursday through Friday period,
widespread liquid precipitation totals of 0.5 to 1.0 inches will
be possible across the Delta, central/southern Sacramento, 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 vary
through the end of the week, beginning around 3500 to 4500 feet
(lowest in Shasta County) late Wednesday before rising to near
5000 to 6000 feet Thursday morning, and further rising above 7000
feet into Friday. As a result, additional mountain snowfall is
expected through early Friday morning. Resultant probabilities of
snowfall exceeding 4 inches with this wave sit around 40% to 70%
above 6000 feet along the Sierra/southern Cascades and above 3500
feet across the Shasta County mountains. Brief periods of breezy
southerly winds will also be possible as each subtle system moves
through, with gusts 20 to 30 mph at lower elevations and gusts up
to 45 mph along the Sierra crest.

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 (Saturday THROUGH Tuesday)...
Ensemble guidance is in generally good agreement on the primary
longwave trough finally progressing through the region on Sunday.
Prior to this though, progressive northwesterly flow aloft will
allow for additional precipitation chances accompanying subtle
perturbations through the early weekend. This will generally
result in a continuation of the active weather pattern through the
weekend, although there are some questions regarding the southern
extent of precipitation, particularly on Saturday. This is
evident in probabilities of 24-hour precipitation for Saturday
around 40% to 70% primarily confined to locations from the
Interstate 80 corridor northward. With Saturday seeing the more
subtle waves, snow levels are expected to remain above pass level
on Saturday.

The more pronounced system that is expected to move through on
Sunday introduces generally widespread 40% to 70% probabilities of
24-hour precipitation exceeding 0.5 inches at low elevations, and
70% to 90% probabilities across the northern Sacramento Valley
and surrounding terrain and along the Sierra/southern Cascades.
Given the synoptic setup, breezy to gusty winds are anticipated
with this system, with some nonzero potential for isolated
thunderstorm development as well. Additionally, snow levels will
likely fall throughout the day on Sunday, with some potential for
accumulating snowfall down to pass level by Sunday
afternoon/evening.

While there is overall good agreement on a transition toward
drier weather into early next week, ensemble guidance notably
diverges with respect to the upper level pattern into the early
week ahead. The favored cluster analysis scenarios are currently
split between immediate ridging following the Sunday system
ejection and lingering northwesterly flow aloft with a slower
eastward ejection. While both scenarios promote a general drying
trend, the latter may introduce some lingering breezy to gusty
wind potential amidst near to slightly below normal temperatures.

&&

.AVIATION...
Areas MVFR/IFR with local LIFR over mountains obscuring terrain
until 03z Wed as Pacific storm moves through interior NorCal.
After 06z Wednesday, potential for Valley fog may lead to local
MVFR/IFR conditions through 16z. Slight chance of isolated -tsra
today between 18z-01z. Snow levels 5500-6500 feet this morning,
lowering to 4500-5000 feet this evening. In Central Valley, areas
southerly surface wind up to 20 kts with local gusts to 30 kts
possible until 18z Tue. Over mountains, areas of southwesterly
surface wind gusts 35-45 kts next 24 hrs.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 7 PM PST this evening for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$

Hazardous Weather Outlook

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