504
FXUS66 KSTO 242147
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
147 PM PST Sun Nov 24 2024

.SYNOPSIS...
A brief lull in precipitation continues through much of this
afternoon, before returning to interior NorCal this evening into
the week ahead. Periods of rain and moderate to heavy mountain
snow are expected through early Wednesday morning, with a brief
cool down then to follow into the Thanksgiving holiday.

*Winter Storm Warning: Until 4 AM Wednesday for elevations above
 5500 feet along the Sierra/ Southern Cascades including
 Interstate 80 and Highway 50.

.DISCUSSION...
As of early this afternoon, latest GOES-West satellite imagery
shows some lingering low to mid level cloud cover for
Valley/foothills locations north of Interstate 80, with some
cumulus development elsewhere along the Sierra as well. Despite
the cloud cover, the only light radar returns as of the noon hour
are along the far northwestern Shasta County mountains. Otherwise,
light to breezy southerly winds prevail with temperatures
trending near normal where cloud cover is lacking and slightly
below normal elsewhere.

While this lull in active weather is expected to more or less
persist through the remainder of the afternoon, there has been a
definitive eastward push over the last few hours of the trough
spinning just offshore of NorCal. Even still, the trough is only
expected to gradually eject eastward moving into the week ahead.
This progression will introduce another period of precipitation
impacts to interior NorCal from this evening through early
Wednesday morning. This precipitation is expected to arrive in
somewhat distinct waves, with areas north of Interstate 80 being
influenced by the trough and moisture advected in the immediate
vicinity of it, while areas from Interstate 80 southward look to
see an additional plume of more concentrated moisture push inland.
While overall highest precipitation totals will continue to favor
the Sierra, this differential between the attendant moisture
should keep Valley/foothills precipitation totals more balanced
(compared to typical patterns favoring higher totals across the
northern Sacramento Valley).

Even with the distinct differences in associated moisture plumes
across the region, current probabilities of exceeding 1 inch of
precipitation sit around 30% to 60% across the Valley and
foothills, with probabilities of 50% to 70% of exceeding 2 inches
of precipitation along the Sierra. Snow levels are expected to
fluctuate somewhat through the event, beginning around 4500 feet
to 5500 feet this evening into the overnight hours, before briefly
rising to 5500 feet to 6500 feet from midday Monday into the
evening, then falling back toward 4500 to 5500 feet overnight
Monday through Wednesday morning. As a result, probabilities of
exceeding 12 inches of snowfall above 5500 feet are around 50% to
90% along the Sierra, with highest probabilities favored from
Interstate 80 southward.

Heaviest snowfall from Interstate 80 southward is anticipated
later in the day on Monday through through Tuesday, with primarily
lingering snow showers by Wednesday as the trough is finally
exiting the region. On the heels of the ejecting trough, a period
of breezy northerly winds is expected on Wednesday. This will help
usher in a push of colder air to interior NorCal, although
coldest temperatures are anticipated Thursday morning. While some
patchy low elevation frost may be possible in the northern
Sacramento Valley on Wednesday, the breezy winds will likely deter
any widespread impacts.

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
Moving toward the end of the week, somewhat split northwesterly
flow aloft initially looks to become replaced by ridging aloft by
next weekend. This will result in winds becoming lighter by
Thursday, with more widespread low temperatures in the low to mid
30s by Thursday morning. As a result, some 30% to 70%
probabilities of low temperatures less than 36F are popping up
across the Valley/foothills for Thursday morning. There is a
slight chances for additional showers from Interstate 80 southward
on Friday as a separate offshore trough moves toward SoCal, but
current probabilities of exceeding 0.1 inches of precipitation are
only around 20% to 40% at this time. Otherwise, with ridging
expected to build in into the weekend, generally dry conditions
with light to breezy diurnal/terrain driven winds accompanying the
pattern.

&&

.AVIATION...
VFR conditions are mainly over Interior Northern California
except for isolated areas of MVFR/IFR conditions in the northern
Sacramento Valley and along the Sierra through 06Z. After 06Z,
more widespread MVFR/IFR expected in precipitation. Southerly
surface winds less than 12 knots become breezy up to 15 kts at
times after 12z. Periodic southwesterly gusts 15 to 25 knots over
the Sierra.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 4 AM PST Wednesday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$