236
FXUS66 KSTO 142253
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
253 PM PST Thu Nov 14 2024



.SYNOPSIS...
Scattered mountain snow, rain showers, gusty winds, and isolated
showers are expected through Friday. Near-freezing low
temperatures in the Valley over the weekend may lead to areas of
frost. A second, weaker shot of showers and mountain snow arrives
Sunday into Monday.

.DISCUSSION...
Isolated showers are making their way across interior NorCal this
afternoon as our current weather system sweeps over Northern CA
today through early Friday and periods of light to moderate snow,
light rain, and breezy winds continue. A few isolated
thunderstorms are also developing across the Sacramento Metro Area
[as of 230pm], and with any thunderstorm that develops there will
be brief periods of heavy rain, lightning, gusty winds, and the
potential for small hail.

The threat continues through this evening, with the National
Blend of Models (NBM) indicating a 15-30% chance of t-storm
development across the Sacramento Valley and adjacent foothills.
The overall steering flow is generally southwesterly which means
any storms that hold together as they move into the mountains, may
result in periods of moderate to heavy convective snowfall along
I-80. Several of the Convective Allowing Models (CAMs) indicate
isolated to scattered thunderstorm development through this
evening, especially over and in the vicinity of the Park Fire Burn
Scar. HREF 1-hour rain rate probabilities of meeting debris flow
thresholds are still around 10%, but we will continue to monitor
RADAR especially close through tonight. Forecast rain amounts are
0.01-0.25" across the Valley and adjacent foothills with
0.25-0.75" over the Northern Sierra/Southern Cascades. Chances to
see a half inch or greater of rainfall accumulations over the
northern Sacramento Valley and mountains/foothills range from 60
to 80% through Friday.

Periods of snow will continue through Friday night with
additional accumulations of 4 to 10 inches, up to 12 inches
forecasted for the Sierra and Lassen National Park area. As a
result, a Winter Weather Advisory will remain in effect for the
Western Slope Northern Sierra/Western Plumas/Lassen Park above
5500 feet through 10 PM Friday. This evening will see showers
begin to redevelop over the Sierra with periods of moderate snow
early Friday morning. 48-hour probabilities (Thu AM - Sat AM) show
a 60-80% chance of totals over 12 inches for elevations above
6000 feet. Snow is expected to taper off Friday afternoon,
eventually diminishing later that night.

Saturday and Sunday forecasted morning temperatures will be near
freezing in the Valley and carry the potential for areas of frost.
Coolest Valley temperatures will be across the central Sacramento
to the Northern San Joaquin Valleys. There is a 30-50% for
overnight low temperatures to be below 35 deg F Saturday morning
for Valley locations east of I-5. This is mainly due to a brief
period of gusty north winds gusting 20-30 mph which will limit
minimum temperatures dipping into the mid to low 30s. On Sunday,
probabilities cover more western portions of the Valley with the
NBM advertising 30-60% chance at temperatures less than 35 deg F.

Northern California will see a return to active weather Sunday
into Monday, as another trough drops down from the Pacific NW
bringing another round of low impacts rain, mountain snow, and
breezy winds. NBM indicates a 40-65% of precipitation totals
greater than 0.25" over the mountains and Northern Sacramento
Valley, including Redding. Probabilities are 15-25% chance for
locations in the Southern Sacramento and Northern San Joaquin
Valleys on Sunday. Scattered showers are forecast to move over
the Coastal Range Sunday morning, before spreading further south
and east across the remainder of interior NorCal later in the
evening.

.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Ensemble guidance and cluster analysis indicate a shortwave
trough moving through the region on Monday, with upper level
ridging building back in behind it over the extended forecast
period. A few lingering mountain showers will be possible on
Monday. Drier conditions return for the rest of the week, along
with periods of breezy offshore flow. The National Blend of Models
(NBM) suggests a 45-85% probability of north to east wind gusts
of 25 mph or greater on Monday and Tuesday, with best chances
mainly in the western portion of the Valley, and Delta, and in the
mountain/foothill gaps and canyons. A warming trend is also
favored with high temperatures returning to near normal by the
middle of the week, around the mid 60s for the Valley.


&&

.AVIATION...
Areas of MVFR/IFR conditions in showers and fog are expected over
interior Northern California. There are chances of thunderstorms
during the daytime hours. Otherwise expect VFR conditions. Local
LIFR conditions and mountain obscuration from clouds and snow are
expected at the Sierra. Surface winds are generally below 12
knots. Gusts are forecast up to 35 knots over the mountains.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 PM PST Friday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$