654
FXUS66 KSTO 211059
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
259 AM PST Sat Dec 21 2024

.SYNOPSIS...
Morning fog potential this morning will be replaced by periodic
chances for precipitation and gusty southerly winds as a series of
weather systems impacts interior NorCal from later this morning
into next week.

.DISCUSSION...
Some pockets of weak radar returns and patchy fog are the weather
highlights early this morning ahead of the first of several
periods of active weather today through next week. Regarding the
fog, patchy fog is expected to develop throughout the Valley again
this morning, densest across the Northern Sacramento Valley.
Models have a 50 to 70 percent chance of visibilities dropping
below 0.5 miles this morning but as the weather system moves into
the area in earnest should end the fog threat by late morning.

Saturday:
Minor travel impacts are expected with rain beginning later this
morning becoming lingering Sierra and adjacent foothills showers
by this evening. Valley rain totals north of I-80 are 0.25-0.75"
with foothills and mountains areas expecting 0.75-1.50". South of
I-80 can expect 0.10-0.50". The heaviest period of precipitation
will be this morning across the NOrthern Sacramento Valley and
northeastern foothills with the highest rain totals along the
Feather River Valley areas. Models show a 60-95% chance of
precipitation amounts greater than an half inch, highest over the
Northern Sierra and northwestern Shasta County mountains.

Snow level start off around 6000-7000`, increasing to
around 7000-8500` south of the Cascades by this afternoon. Light
snow accumulations are forecasted with only a dusting to a few
inches expected for much of the Sierra and up to 6-8" across
Lassen NP. As this waves tapers off south of I-80 over the Sierra,
our next wave will repeat again moving south and eastward from
the Coastal Range Sunday late morning/afternoon.

Sunday AM - Monday Afternoon
There is some uncertainty regarding the timing of the wave with
some models moving the wave across the area Sunday morning but
others keeping the next wave of weather at bay until the early
afternoon. Overall, forecasts have been trending lower, possibly
highlighting the potential for the delay incoming weather.
Thankfully, impacts looks to be minor again with a drier wave of
rain compared to Saturday`s weather.

Rain totals will be a trace to 0.50" in the Valley increasing as
you move northward and upwards in elevation. THe foothills an
mountains will be 0.25-1.00", highest over northwestern Shasta
County. Snow is not expected to accompany this wave as snow
levels will be 7500-8500` during the bulk of the expected
precipitation. That being said some light flurries may be
possibly over the mountains but no significant accumulation
forecasted at this time.

Monday Afternoon - Tuesday Night (Christmas Eve Night)
Within the short term, this will the wettest period with minor to
moderate travel impacts from rain and snow. Snow levels Monday
afternoon start around 7500-8500`, increasing to 8000-9000` Monday
night before levels plummet Tuesday morning becoming 4500-5500` by
Tuesday evening. Snow totals over the Sierra will be 4-8" up to a
foot along the crest and near Lassen NP. Areas south of Hwy. 50
is forecasted to have the highest totals with models showing a
40-60% chance of totals greater than 6 inches across the Sierra.
The heaviest period of snow will be late Tuesday morning into
early Tuesday afternoon. Slick roads, chain controls, and snow
covered roads are possible so please exercise caution if traveling
this holiday and check quickmap.dot.ca.gov or dial 511 for the
latest road conditions!

For rain, totals in the Valley are 0.50-1.25" north of I-80 and
0.10-0.50" southward. The foothills, Northern Sacramento Valley,
and mountains are forecasted to see 0.50-2.00", up to 4 inches
over the Coastal Range and northwestern Shasta County. Similarly
to before as you travel north and upwards in elevation, you
should expect rain totals with the heaviest period of rain Tuesday
morning. Models show a 50-80% chance of an inch in the Valley
north of I-80 and a 50-80% chance of 2.50" occurring over the
mountains and Northern Sacramento Valley. Lastly, Tuesday
afternoon will see a 10-20% chance of thunderstorms, primarily
over the Delta initially, spreading to the Valley and foothills
areas throughout the day.

Lastly, Monday evening into Tuesday afternoon will see breezy
south winds, strongest over the northeastern foothills and over
the Sierra. Gusts of 15-35 MPH is expected across the lower
elevations and gusts up to 40-45 MPH over the Sierra. Afternoon
highs will remain in the 50s today with a slight uptick in
temperatures south of the Interstate Sunday and Monday getting
into the low 60s.

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Wednesday (Christmas Day) looks to remain relatively dry with only
light north winds to speak of. Forecast have the next wave nudge
its way over the Coastal Range Wednesday night, arriving more
earnestly on Thursday.

On Thursday, the active pattern resumes as another storm system
brings more rain and mountain snow chances through Friday. The NBM
shows a 40 to 70% chance, up to 90% north of Redding, of
exceeding 1.00 inch of rain north of I-80 with this system and a
30-55% chance for 6.00 inches or more of snow at around 5500-6000
feet and higher. Highest precipitation amounts with both systems
will be focused over the northern Sacramento Valley, southern
Cascades, Lassen NF/NP, and the Sierra and adjacent foothills.
Additionally with these systems, southerly winds are forecast to
gust 15 to 30 mph with a 15 to 30% chance of gusts exceeding 30
mph. There is still much uncertainty with this later week system,
so stay tuned to the forecast for updates as we move through the
weekend when ensembles and cluster analysis come into better
agreement.

&&

.AVIATION...

Areas of MVFR/IFR/LIFR conditions in BR/FG and/or low ceilings
until 15Z-18Z Saturday. Periods of MVFR/IFR conditions in showers
until around 00Z Sunday, with lingering Sierra showers until
Sunday morning. Locally breezy southerly wind gusts up to 15-20
kts across portions of the northern and central Sacramento Valley,
and up to 20-30kts over the Sierra Sat 15Z-00Z Sun. Otherwise,
surface winds generally below 12 kts.

&&

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

$$