Winter Storm Watch 2, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
1022 PM PST Sat Jan 7 2017

.Synopsis...
Heavy rain and flooding concerns arrive late tonight and continue
into Monday. The heaviest rain is expected during the day Sunday,
along with gusty winds. Another wet storm arrives Tuesday into
Wednesday with continued flooding concerns and heavy mountain
snow.

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.Discussion...
Main atmospheric river plume just begining to spread over NorCal
this evening and will continue into Sunday night. The heaviest
rainfall is currently projected between 11 am and 4 pm Sunday this
will also coincide with wind gusts to 45 mph. Expect widespread
small stream flooding and potential downed trees and power
outages. current forecast is on track and no updates needed.

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.Previous Discussion...
Scattered precipitation continues across the forecast area,
something of a lull from the heavier precipitation that fell this
morning. Rain amounts so far are generally around a half an inch
to an inch, locally to around 2 to 2 1/2 inches in the northern
Sierra. Rain is expected increase again this evening and
overnight. The heaviest rain is expected during the day Sunday.
Snow levels in the Sierra rapidly rose through the day as warmer
air advected in, with snow levels over 3000 feet over Shasta
County, over 8000 feet over the northern Sierra. Snow levels
started the day very low over Shasta County, with 2-3 inches of in
Redding, due to cold air drainage with northerly winds. The
Sierra saw just a couple of inches before the snow levels rose
above pass levels. Because of this, Donner Pass had less snow than
Redding, a rare occurrence. A Winter Weather Advisories have been
cancelled, due to the high snow levels. The Sunday system will be
a rain event for all but the high peaks.

Gusty winds will return Sunday morning, and continue through the
day. A Wind Advisory has been issued for the Delta and Valley
(except the northern Sacramento Valley) through 6 pm Sunday.

There could be some thunderstorms Sunday evening with decent
elevated instability from cold air aloft. Have added a slight
chance of thunderstorms for the northern and central Sacramento
Valley.

A Flood Warning is in effect for the Wilton area, due to projected
flooding of the Cosumnes River at Michigan Bar late Sunday morning.

The next system Tuesday and Wednesday will not be as wet, but will
add to the stream and river rises from the weekend to Monday
system. A Flood Watch continues through Wednesday. In addition to
heavy rain, heavy snow is expected in the mountains. There could
be 2 to 3 feet of snow above 5000 feet, potentially more over the
peaks. EK

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.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Not much change in the extended forecast. Wednesday continues to
look wet as that is part of the second wet storm expected to hit
NorCal on Tuesday-Wednesday with snow levels below passes at
approximately 4000-5000 feet. The models continue to struggle on
how the wet pattern will look between Thursday through Saturday.
At this point, it looks like Thursday will at least see some
scattered showers (GFS), but it could be more widespread (ECMWF).
Both models are showing a break Friday with an additional storm
arriving either early Saturday (GFS) or late Saturday (ECMWF).
Chance pops continue to be best bet at this time. Snow levels
remain moderate through the extended period. JBB

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.AVIATION...

MVFR/IFR ceilings and visibilities are expected these next 24
hours as another system moves onshore. South winds will be
increasing tonight and will be strongest in the S Sacramento
valley and N San Joaquin valley by Sunday morning. Heavy rainfall
with MVFR/IFR conditions expected Sunday with precip tapering off
around 21Z for the N Sac valley and around 00Z for the S Sac
valley. Southerly winds will weaken tomorrow evening. Wilson

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.STO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Wednesday afternoon for Burney Basin /
Eastern Shasta County-Carquinez Strait and Delta-Central
Sacramento Valley-Clear Lake/Southern Lake County-Motherlode-
Mountains Southwestern Shasta County to Northern Lake County-
Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-
Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta
County-Southern Sacramento Valley-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.

Wind Advisory from 6 AM to 6 PM PST Sunday for Carquinez Strait
and Delta-Central Sacramento Valley-Northern San Joaquin Valley-
Southern Sacramento Valley.

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