Winter Storm and Winter Weather in California, January 16 to 17, 2020

Area Forecast Discussion
National Weather Service Sacramento CA
323 AM PST Thu Jan 16 2020

.SYNOPSIS...
A Winter Storm moves through the area into early Friday bringing
periods of rain, snow, and gusty winds to the area. Unsettled
weather continues over the weekend into next week.

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.DISCUSSION...
Radar and satellite show the storm moving ashore northwest
California early this morning. The main area of precipitation is
along the cold front while a few showers have developed across
the northern half of the forecast area in the region of warm-
advection ahead of the cold front. Winds have picked up overnight
across the northern half of the Sacramento Valley as the surface
gradient has tightened (RDD-SAC now over 6 mbs). Gusts in the mid
40s mph have been reported from about the Chico area northward.

Current temperatures are very mild compared to 24 hours ago given
the wind and cloud cover with readings in the 20s and 30s in the
mountains and mainly 40s to lower 50s in the Central Valley.

The cold front will move into interior NorCal this morning
accompanied by a band of moderate to heavy precipitation which may
result in ponding of water on road surfaces. This area of heavier
precipitation is expected to reach the Redding area around
sunrise, then move southeast and reach the Sacramento region
around late-morning. Showers and a few thunderstorms will be
likely behind the front this afternoon.

Over the mountains, snow will increase early this morning north
of Redding with rapidly deteriorating conditions expected. Heavy
snow will develop across Donner Pass on I-80 by mid to late
morning with many hours of 2-3 inch/hour snowfall rates expected
continuing into this evening as mid-level lapse rates steepen
behind the front. Snow levels across most of the area will range
from 2-3k ft by late this afternoon. Snowfall accumulations will
be measured in feet with 1-3 ft expected above about 3k ft.

Precipitation becomes showery late tonight with chances retreating
to the northern mountains on Friday as broad ridging moves back
into the area. Models continue to back off on the weekend system
with precipitation mainly limited to the coastal and northern
mountains at this time.

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.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Upper ridging exits early next week with another winter system
moving in. Timing is not certain at this point, but for now have
chances of precipitation spreading in over the area as early as
the afternoon on Monday, which is Martin Luther Kings Birthday.
This is from a wave associated with an upper low centered off the
coast of Canada moving inland.

Ensemble averages suggest an early estimate of around a foot of
snow could be possible over 6500 feet in the northern Sierra. This
could cause travel difficulties during the return period at the
end of the holiday weekend, so monitor the forecast closely if you
have plans of mountain travel early next week, especially late
Monday through Tuesday. Additional unsetled weather is possible
through mid week. Continue to expect changes to the timing of
these systems. EK

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.AVIATION...
VFR conditions are expected to deteriorate this morning.
Widespread rain is expected to spread from north to south during
this time frame, dropping most sites into the MVFR category.
IFR/LIFR conditions will be possible at times too. Winds are
increasing over the northern Sacramento Valley with gusts of up to
45 kt possible through the 18z. Wind gusts over the rest of the
Sacramento Valley and the northern San Joaquin Valley could gust
to 25-30 kt through 23z. For the mountains, wind gusts up to
around 50 kt to 60 kt are possible today. Heavy snow will bring
poor visbility above 2000 feet (IFR/LIFR), spreading from the
northern mountains currently to the northern Sierra by around 18z.
EK

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 6 AM PST Friday for Burney Basin /
Eastern Shasta County-Clear Lake/Southern Lake County-Motherlode-
Mountains Southwestern Shasta County to Northern Lake County-
Northeast Foothills/Sacramento Valley-Shasta Lake Area /
Northern Shasta County-West Slope Northern Sierra Nevada-Western
Plumas County/Lassen Park.

Wind Advisory until 10 AM PST this morning for Central
Sacramento Valley-Northern Sacramento Valley.

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