High Wind in California, December 27 to 28, 2020

Area Forecast Discussion...CORRECTED
National Weather Service Hanford CA
501 PM PST Sun Dec 27 2020

Updated air quality section

.SYNOPSIS...
Expect a more significant weather maker to bring more rain and
mountain snow later today through Monday as a cold storm system
moves in from the Pacific. Dry weather will return on Tuesday and
Wednesday as this storm moves to the east of the region. A weaker
system could bring a slight chance of precipitation on Thursday,
mainly north of Kern County.

&&

.DISCUSSION...
The second in a series of storms is currently at the door-steps
of Central California. This storm will keep winter weather in
progress across the region as rain and snow will enter the region
later tonight as the associated cold front makes landfall. While
regional Doppler radar imagery is showing light warm frontal
precipitation over the mountain ranges, the trend will be to have
these showers dissipate ahead of the strong storm system about to
enter the district just before midnight tonight. Based on surface
observations from around the area, current snow levels remain at
around 6000 feet as a moderate southerly wind flow blows in the
warm sector ahead of the cold front still expected to push in
overnight into early Monday morning. Therefore, will not expect
snow in the foothills as the trend will be to have snow levels
drop to near 4000 feet during the night. Winter Storm Warning and
Winter Weather Advisories will remain in effect for the overnight
hours above 4000 feet for the Sierra Nevada from Yosemite down the
Kern County Mountains around the Grapevine area. With this storm,
winds will be a concern, but, will not expect a very strong wind
event. While surface pressure gradients from KSFO and KLAS are
directed offshore at between 3 and 5mb, only locally breezy
conditions will be felt. The addition of a jet max will support
strong winds over the Crest of the Sierra Nevada.

Model confidence continues to grow on the possible storm track
early this week. While some uncertainty is still shown how deep
the upper low will dig toward Southern California, Central
California is clearly in the path of the storm track as
significant precipitation is be expected from late tonight through
Monday. Model moisture analysis is still not showing this to be
an Atmospheric River event, but, as the upper low approaches the
Central California coast-line, will expect enough wrap-around
moisture to support heavier precipitation values across the
region. Along with moisture being pulled into the area, upper air
analysis is still showing good dynamic and mechanical lifting
later tonight through Monday. Difluent flow along with jet level
west to southwest winds of 70 to 90 knots will provide the
mechanism for abundant precipitation. In addition, the cold core
of the upper low is still expect to move into the region late
tonight and lowering freezing temperatures down below 4000 feet.
This scenario warrants the Winter Weather products currently
posted across the Sierra Nevada and the mountains around the
Grapevine. By Monday morning, Interstate 5 around the Grapevine
could see snow and impact travel.

Convective activity is still not favored across Central
California outside of Kern County as the current trajectory of the
upper low is still looking like a coastal hugging solution. Based
on its position and the time of day, thunderstorm activity may be
confined to the coastal regions as only weak instability is able
to penetrate into the Central Valley during the lows passage
across the area. Yet, the convective activity may still support
bursts of very heavy rain and snow over the Kern Mountains as
travel may become very difficult.

By Tuesday and Wednesday, models move the disturbance east and
into the Four Corners region as a northerly flow moves into the
state. Will see a shot of cold air (post cold front) move into the
region as temperatures drop below seasonal normals. Freezing
temperature will seem more likely toward the middle of the week as
cold and dry air settle over the region. With a ridge expected
toward mid-week, dense fog will present itself a problem across
the San Joaquin Valley. The last day of the year will see another
disturbance cross Northern California and skirt the area near
Yosemite. Widespread precipitation seems unlikely, but, the Sierra
Nevada near Yosemite could get brushed with light precipitation
during the storms passage. Fog will be observed this week with the
end of the week event helping to disturb the possible fog
situation for a day or two. While uncertainty is high, New Years
may start with a ridge overhead before converting to a zonal flow
pattern by next weekend.

&&

.AVIATION...
Expect IFR conditions with mountain obscurations due to
precipitation over the Sierra Nevada and the Kern County
mountain areas for much of today into Monday. MVFR ceilings and
visibility due to showers are possible in the San Joaquin Valley
after 03Z Monday. VFR conditions will prevail elsewhere over the
central California interior during 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...
Winter Weather Advisory from midnight tonight to noon PST Monday
for CAZ192.

Winter Storm Warning from midnight tonight to 6 PM PST Monday
for CAZ193-194.

Winter Weather Advisory from 3 AM to 6 PM PST Monday for
CAZ195>197.

&&

Public/Aviation.....Molina
PIO/Social Media....DS

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