Winter Storm Watch 7, NWS Hanford, CA

Area Forecast Discussion
National Weather Service Hanford CA
356 AM PDT Thu Oct 21 2021

.SYNOPSIS...
Isolated showers are possible towards the north sectors of the
district today. Another system will bring light showers to the
northern portion of the forecast area Friday afternoon and
evening, along with breezy conditions. A much stronger storm
system will impact the region Sunday and Monday, bringing moderate
to heavy rain for a majority of the forecast area. Calmer pattern
to resume after next Tuesday.

&&

.DISCUSSION...
Some mid and upper level clouds moving onshore across Central CA
as well as a few showers crossing over the north sectors of the
San Joaquin Valley and Yosemite area. Water vapor images show the
district in a long fetch of moisture extending well east over the
Pacific Ocean. A Moderate westerly flow aloft will prevail today
with a slight warming to near normal temperatures. Upper level
disturbances moving through flow may combine with the high
moisture to generate a few showers over the north sectors of the
district today.

The ensemble solutions appear in fair agreement with the
operational models into Monday. A short wave trough will approach
the NCal coast Thursday night. This system will bring some rain
along a cold front into the central valley during the late
morning Friday and in the early afternoon in Yosemite. The upper
trough will shift east of the central sierra towards the Great
Basin Friday afternoon. The front falls apart as it pushes trough
the central valley due to the lack of dynamic forcing. Higher
resolution models show a strong northwest flow behind the front.
Conditions should turn cooler and breezy across the valley with
gusty wind through the mountain passes of the Kern County
Mountains and Desert Friday afternoon through Saturday. Models
show some light rain accumulations over the Tehachapi Mountains
and surrounding foothills Friday night to Saturday morning. A
cool onshore flow will continue over CA on Saturday as a
disturbance moves brings another front through NCal. A lull in
activity will occur on Saturday in central CA.

A much larger and stronger system is expected to dive out of the
Gulf of Alaska late Saturday night and approach the region Sunday
morning. The upper trough will move off the PacNW coast Sunday.
Models prog a long fetch moisture from the Pacific to NCal with
this system. The upper trough digs well south over the central CA
coast Monday morning bringing the atmospheric river of moisture
into Central CA. This will bring a good potential for rainfall
across much of the district Sunday and Monday. A strong upper
level flow from the west to southwest will lead to a heavy threat
of rain over the central sierra due to a favorable upslope wind
flow over mountain terrain. The period of the heavier rainfall is
expected to be late Sunday night to Monday morning. This will be
a rather warm system with snow levels starting as high as 10,000
feet Sunday afternoon, staying to around 9000 feet through Monday
morning. Snow levels are expected to drop to around 7000-7500 feet
Monday afternoon. This system will likely require a Winter Storm
Watch above 9000 feet with a Flood Watch below 9000 feet. 1-2
inches of rainfall are possible in the north sectors of the San
Joaquin Valley through Monday afternoon, with 4-6 inches of
rainfall possible in the Sierra Nevada below 9000 feet. Above 9000
feet may receive 1 to 3 feet of snow through Monday evening as
well. With the heavy rain includes the possibility of debris flow
flooding, especially over burned areas over the last year or two.
Strong winds may accompany the passage of the cold front Monday.
Conditions should turn breezy in the SJ Valley and west side
hills while much windier conditions should occur over the
Tehachapi Mountains and the Mojave Desert Area.

The storm system is progged to exit the region by late Monday or
early Tuesday. A few upsloping showers may persist late Monday
into Tuesday after the cold front passes through the region. A
drier and calmer weather pattern is expected thereafter.

&&

.AVIATION...
Mountain obscurations over the Yosemite high country through 20Z
Thur. Otherwise VFR conditions will prevail across Central
California through at least the next 24 hours.

&&

.AIR QUALITY ISSUES...
None.

&&

.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.

&&

.HNX WATCHES/WARNINGS/ADVISORIES...
None.
&&

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