River Flood Warning 34, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
401 AM PST Wed Feb 15 2017

.Synopsis...
Wet weather returns later today with several rounds continuing
into next week.

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.Discussion...
Upper ridge is beginning to give way as the developing storm over
the eastern Pacific approaches NorCal. Clouds have been increasing
overnight and some areas of light precipitation have begun to show
up on radar off the northwest coast of California. Early morning
temperatures are considerably milder compared to the past few days
and generally range from the 20s and 30s in the mountain valleys
to the mid 40s to lower 50s elsewhere.

Some light warm-advection precipitation will develop across far
northern California today, but much of the region should remain
dry until tonight.

Heavier precipitation is currently expected to move through
the region late tonight into Thursday morning. Precipitation from
this first storm will be focused along and north of I-80 where
the Sacramento Valley may see 0.50 up to 1.50 inches while the
foothills and mountains may receive around 2-4 inches. Amounts to
the south of I-80 will be lighter.

This storm is now looking a bit colder than previously projected.
Snow levels now look like they should hover between 5000-6000
feet, which would impact major northern Sierra Nevada passes.
This would additionally mean less runoff into northern Sierra
reservoirs. A quick 6 to 12 inches of snow will be possible at
elevations above 5500 feet, with up to 2 feet possible across
Lassen Park and ski resorts. A Winter Storm Watch has been issued
to address this.

It's looking like the brunt of Friday's storm is heading toward
SoCal with lighter QPF and not as much wind for NorCal. However,
with snow levels remaining around 5-6K, winter weather impacts may
continue across the higher elevations of the northern Sierra
Nevada.

Showers expected to taper off Saturday as brief ridging returns.

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.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)
Sunday looks to be somewhat in between systems under a flat
ridge. We will see plenty of cloudiness and lingering showers,
especially over the mountains.

The next frontal system will move inland Mon with increased
dynamic and strong southerly low level winds into Tuesday. The
stress on the Oroville Dam system will be somewhat lessened as
Sierra Nevada snow levels fluctuate around 4000 to 5000 ft Sunday
to Tuesday. This limits the amount of runoff making it down into
the reservoirs. Early rainfall estimates Sunday through Tuesday
night are from 1 to 2 inches in the Valley and 3 to 5 inches in
the mountains with 1 to 3 feet of snowfall above roughly 5000
feet. The USA West Coast Atmospheric River Tool indicates the
precip water plume should affect the area mainly from Monday into
Tuesday. JClapp/IDM/JHM

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.AVIATION...
Mainly VFR conditions next 18 hrs with light winds across
interior NorCal with the exception of some shallow fog this
morning from KSMF southward mainly through 17z. Light
precipitation should spread across northern interior NorCal
tonight into early Wednesday with brief MVFR conditions.
Increasing southerly winds this evening into Thursday. JClapp

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late tonight through Thursday afternoon
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

Flash Flood Watch through Thursday morning for Carquinez Strait
and Delta-Central Sacramento Valley.

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