Alta Sierra, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

828
FXUS66 KSTO 022030
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1230 PM PST Thu Jan 2 2025

.SYNOPSIS...
A weather system approaches late tonight, bringing widespread
precipitation, moderate to heavy mountain snow, gusty southerly
winds, and isolated thunderstorms through Friday. Dry and warming
weather will follow over the weekend and into next week with
periods of gusty north to east winds.

&&

.DISCUSSION...
Latest GOES-west visible satellite imagery shows partly to mostly
cloudy skies across much of interior northern California on this
Thursday afternoon. Temperature observations are currently
trending approximately 5 to 10 degrees warmer than this time
yesterday, valid at 1230 PM PST with 50s and 60s in the Valley
and foothills, and 40s to 50s in the mountains. Mostly dry weather
will continue through the day today, with the exception of a few
light showers up in the northern mountains.

A quick moving weather system will approach the area tonight and
move inland through the day tomorrow. This system will bring
widespread precipitation, moderate to heavy mountain snow, gusty
southerly winds, and isolated thunderstorms on Friday.
As precipitation spreads inland from west to east tomorrow, latest
WPC guidance shows storm total rain amounts ranging from 0.10-1"
in the Valley with 0.50-2" in the foothills and mountains. The
National Blend of Models (NBM) continues to show a 10-20%
probability of thunderstorms in the Valley and foothills on
Friday. This is consistent with CAPE on the Extreme Forecast Index
(EFI) and the Convective Allowing Models (CAMs). The most likely
timeframe for any thunderstorms is between 10 AM and 8 PM. Rain
rates are currently expected to remain below debris flow
thresholds for burn scars.

Moderate to heavy mountain snow will bring impacts to mountain
travel tomorrow as well. Snow amounts have trended higher since
the previous forecast package, and snow levels have trended
slightly lower. As a result, we have issued a Winter Storm Warning
for elevations above 5500 feet in the northern Sierra Nevada and
southern Cascades from 7 AM to 10 PM PST Friday. The NBM has a 55
to 85 percent probability of snow amounts of 6 inches or greater
over 24 hours. High resolution guidance also indicates snow rates
of 1 to 2 inches per hour at times tomorrow. Snow levels initially
are around 5500 to 6500 feet in the morning, lowering to 4500 to
5500 feet in the afternoon. Travels delays from snow covered
roads, chain controls, road closures and/or significant reductions
in visibility will be possible. Gusty southerly winds will
accompany this weather system as well, and strongest winds are
expected in the northern/central Sacramento Valley, adjacent
foothills and in the mountains.

On Saturday, a few mountain showers and snow showers will be
possible in the morning, but overall drier weather returns to the
region. Upper level ridging will build back into the region over
the weekend, bringing drier and slightly warmer weather that
continues into the extended forecast period. Be sure to stay up to
date with the latest weather forecast at weather.gov/sto and road
conditions at quickmap.dot.ca.gov! /KH

&&

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Ensemble guidance and cluster analysis indicate upper level
ridging to be the dominant synoptic feature over the extended
forecast period, allowing for dry and warmer weather to prevail
throughout next week. High temperatures will be near to above the
early to mid January climatological normal, with Valley
temperatures in the mid 50s to start off the week, rising to the
mid 60s by the middle of next week as the ridge builds over the
Eastern Pacific. Periods of gusty north to east winds are also
favored over this timeframe, with the National Blend of Models
(NBM) suggesting a 40 to 70 percent probability of wind gusts of
30 mph or greater along and west of Interstate 5, and in the
mountain/foothill gaps and canyons each day next week with the
best chances on Tuesday. /KH

&&

.AVIATION...
A weather system is forecast to bring MVFR/IFR conditions from
gusty winds and precipitation to Interior NorCal beginning 12Z on
Friday. Local MVFR/IFR conditions are possible north of I-80
until the weather system moves through. Southerly wind gusts of 15
to 25 knots will be possible on Friday when the weather system
moves through the area.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 7 AM to 10 PM PST Friday for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$