Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 182321

Area Forecast Discussion
National Weather Service Sacramento CA
321 PM PST Thu Jan 18 2018

Active weather pattern continues with a storm system moving
through the area into Friday, bringing mountain snow and Valley
rain. A weaker cold storm system is expected Sunday into Monday,
bringing accumulating snow in the mountains. Another system
arrives mid week.


A cold front with the main frontal band of precipitation is
moving across northern California. This band is currently north of
I80, but will spread precipitation across the rest of the area by
early evening. Cold air behind the front will drop snow levels
rather quickly. This is already happening at Shasta Dam, where
snow levels were over 8000 feet this morning, down to 5400 feet at
Shasta Dam at 2 pm. Snow levels around Donner Pass have been
around 8000 feet, but will drop overnight, lowering to around
2500-3500 feet by early Friday.

A band of stronger convection could bring a period of heavy rain
and some lightning early this evening over Shasta County.

Snow totals have lowered some, to around 8 to 12 inches for the
northern Sierra through Friday. The heaviest snowfall is expected
this evening through early Thursday morning as the front exits the
area. Travel for the I-80 and US 50 corridors will become
slippery. Gusty southwest winds 30 to 50 mph with gusts to around
65 mph over ridges when combined with snow could bring poor
visibility. Winter Storm Warning continues for the northern Sierra
and mountains of western Plumas and Lassen County, with a Winter
Weather Advisory for the mountains southwestern Shasta County to
northern Lake County, through 4 pm Friday.

The precipitation will become more showery Friday, gradually
tapering off through the day. There is a slight chance of
afternoon thunderstorms over the northern and central Sacramento
Valley. A short wave ridge of high pressure will develop Saturday
with the potential for clearing skies before the next weather
making system arrives Sunday.

The next system arrives Sunday, spreading precipitation across the
area. Heaviest amounts of snow are expected over the northern
mountains, where 6 to 12 inches are currently projected through
Monday. The northern Sierra is expected to see lighter amounts,
more in the 2 to 5 inch range. EK
The weather system that moves in on Sunday will move out of the
area on Monday. Showers could linger throughout the day, but
models have decreased the expected precipitation for Monday.
Valley locations could see a few hundredths up to a tenth of an
inch of new precipitation, with only slightly more precipitation
likely for the mountains. Snow levels will remain low, around 4000
to 5500 feet. Mountain locations could expect half an inch to an
inch of new snow.

After Monday, the forecast becomes more uncertain. The wet pattern
is expected to continue with another winter storm possible
around midweek, though models differ on timing and impacts of this
system. For now, the system is forecast to move into the forecast
area on Tuesday and impact the area through Thursday. Models
currently depict the storm track a bit farther north with this
system. As such, areas north of Interstate 80 will bear the brunt
of this system. HEC

MVFR/IFR conditions, local IFR, due to low ceilings/BR through
the evening. Precipitation continues to spread southeast through
Thursday with IFR conditions over the Sierra, and MVFR/IFR
conditions in the Central Valley. Could see a few gusts to 20 kts
in the northern Valley, higher gusts over the mountains.


Winter Storm Warning until 4 PM PST Friday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Weather Advisory from 7 PM this evening to 4 PM PST
Friday for Mountains Southwestern Shasta County to Northern Lake
County-Shasta Lake Area / Northern Shasta County.


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