Area Forecast Discussion
Issued by The National Weather Service
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FXUS66 KSTO 222155

Area Forecast Discussion
National Weather Service Sacramento CA
255 PM PDT Thu Apr 22 2021

Dry and warm weather through the end of the week. Widespread rain
and significant snow return by Sunday into early next week with
mountain travel impacts possible.


Upper level ridging is building into the region today and that is
bringing quiet weather with mostly clear skies. We are continuing
to see good flow through the Delta and that is going to continue
into the overnight. That is holding temps down some in the Delta
and into the Sacramento area this afternoon. Some marine stratus
made it into the Valley this morning and currently the Fort Ord
profiler has a healthy marine layer of about 3000 feet. Given the
deep marine layer, good flow through the Delta and what we saw
this morning it seems very reasonable to see some low level clouds
in the Delta and Sacramento area tomorrow morning. Any marine
clouds that make it into the Valley should clear quick by the mid
morning and Delta flow will keep temps cooler once again tomorrow.
Also as we head into the afternoon and evening we will see high
level clouds build into the region ahead of an approaching short
wave trough.

Our weather will be changing as we head into the weekend with more
active weather expected. A short wave trough will push over the
northern part of the state Friday night into Saturday and will
also push a cold front into the region. This will bring light
shower chances mainly to the northern mountains. The front will
stall out over the region on Saturday and a deeper stronger trough
will push it south on Sunday. As this deeper trough approaches
NorCal we will see showers increase from north to south Saturday
evening into Saturday night and we can expected widespread rain
and snow Sunday morning into the afternoon. Activity will become
more showers over the Valley during the afternoon Sunday and over
the mountains Sunday night. Models are building in some post
frontal instability Sunday afternoon mainly form Sacramento north
to Redding. With the trough axis approaching NorCal during this
time some isolated thunderstorms are possible in this region of

Shower activity will continue into Sunday night with the best
chances over the mountains as troughing remains in place over the
state. The majority of mountain snow accumulation can be expected
on Sunday. Snow levels are looking to be between 4500-5500 but
will fall to 3500-4500 feet for a time Monday morning. Despite the
snow coming during the day on Sunday it will likely come down at
a high enough rate for it to accumulate on road surfaces and cause
travel impacts. A Winter Storm Watch has been issued for the
southern Cascade and northern Sierra for Saturday night into
Monday morning. Snow totals are looking to be 8-16" with locally
higher amounts above 7000 feet. Rain totals in the Valley are
looking to be between 0.15-1.15" and Foothill totals 0.75-2.15".

Breezy onshore winds are also expected on Saturday and Sunday.
Valley gusts to 30 mph will be possible and we could see mountain
ridge gusts up to 50 mph. This trough will also bring in much
cooler air and we will see daytime highs as much as 25 degrees
cooler Sunday compared to Friday and 15-25 degrees below average.
These highs look to remain warm enough to not set any new cold
highs for that day but we will likely be within a few degrees of
these records.



While the bulk of this weekend`s system will have wrapped up,
some lingering rain and snow showers are expected into Monday
afternoon. Best chance will be in the foothills and mountains
where the National Blend of Models paints a 25 to 40 percent
chance from Shasta County south to Yosemite National Park.
Longwave trough axis will push inland on Tuesday as an upper level
ridge starts to rebuild over the Pacific Northwest and far
northern California. Ensembles generally favor ridging through the
end of the next week with day-to-day warming. 80s will become
more common in the Sacramento and northern San Joaquin Valley
around Thursday. // Rowe


VFR conditions are generally forecast to prevail across northern
interior California over the next 24 hours. The exception to this
is around the Delta and the Sacramento area terminals where marine
stratus may bring brief periods of MVFR/IFR-level ceilings around
sunrise Friday. Locally breezy westerly winds with gusts up to
around 25 kt will impact the Delta region; elsewhere, winds will
generally remain at/below 15 kt through the TAF period.


Winter Storm Watch from Saturday evening through Monday morning
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.


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