Winter Storm Warning 3, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
223 AM PDT Tue Apr 19 2022

.SYNOPSIS...
Unsettled weather this week as multiple systems impact interior
Northern California. Rain and mountain snow are expected today.
The second and more impactful system occurs Wednesday into Friday.

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.DISCUSSION...
Areas of rain are moving through the region. Snow levels are high
to start but are expected to lower to 4000 to 5000 feet over the
far Northern Sierra/Lassen Park area over the next several hours
while further south snow levels should lower between 5 and 8 am
this morning down to around 5000 feet. Have extended the Winter
Weather Advisory further northward due to moist upslope flow
overnight into the early morning hours expected to produce some
decent amount of snow above 5000 feet. Models are hinting at some
isolated thunderstorm activity later this morning and afternoon
over the far north end of the valley and portions of the northeast
foothills and adjacent mountains where we could see some
convergent zones set up. Most of the valley rain will move
through by mid morning with maybe a few isolated showers
persisting into the afternoon. The one exception may be the far
northern part of the valley where some isolated shower and
thunderstorm activity could persist into early evening. All
activity should die down by mid to late evening per current models.

The next cold front is back near 150W in the Gulf of Alaska. A
lot of moisture out in front of the cold front will move over the
region late today and tonight so some upslope areas may have a
chance to see some precipitation ahead of the front especially
over the far northern Sierra and southern Cascades.

By Wednesday morning the next front should be starting to move
over the northern areas. The front will be slow to move southward
so it may not be until Wednesday evening before the Sacramento
area starts to see some precipitation. Winds will increase early
Wednesday over the north end of the valley and increase during the
day further south. Gusty winds should persist into early Thursday
before decreasing. We may need a wind advisory for portions of the
Sacramento valley during this time period with the gust potential
35 to 50 mph over a good portion of the valley. The strongest
winds are expected over the north end of the Sacramento valley.

The trough will deepen over the region on Thursday and portions
of the Sacramento valley and adjacent mountains north of the
Sacramento region may start to see some isolated thunderstorm
activity in the morning. During the afternoon is when the greatest
threat over the entire region for thunderstorms will occur.
Currently profiles look like they would produce heavy rain and
small hail.

By Friday morning the central part of the trough moves over
Nevada with the back end of the trough still over the region.
Showers are expected to continue but should gradually taper during
the day ending in the evening. Best chances look to be over the
eastern side of the valley and adjacent foothills and mountains.

This will be a very good late season precipitation event for the
region with at least 1 to 2 feet of snow over the higher
elevations, a half inch to an inch and a half of rain in the
valley and 1 to 3 plus inches for the foothills and mountains.
Thunderstorms may end up producing locally higher amounts.
&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...

Good agreement with a ridge of high pressure building over the
weekend with warmer temperatures and dry conditions. These
conditions will persist through Monday. Next Tuesday a trough
moving into the Pacific Northwest will start to nudge the ridge to
the east. The far northern part of the state including the north
end of the valley may have a chance to see a little bit of
precipitation from the tail end of that trough.

&&

.AVIATION...

Mainly VFR conditions expected, although local MVFR cigs possible
with -RA thru 19Z. MVFR to IFR conditions over the Sierra thru 00-
06Z Wednesday. Drier in the Valley after 19Z, although some
lingering isolated showers still possible over the mountains.
Onshore winds from 5-15 knots through the period.

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM PDT this morning for Western
Plumas County/Lassen Park.

Winter Weather Advisory until 2 PM PDT this afternoon for West
Slope Northern Sierra Nevada.

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