Flash Flood Watch 2, NWS Sacramento, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
406 AM PST Mon Dec 1 2014

.Synopsis...
Unsettled weather continues through the week with a continued threat
of precipitation. Lingering precipitation over portions of interior
Northern California today, mainly to the north of Interstate 80,
with snow levels around 7000 feet. A wetter system will bring more
precipitation Tuesday and Wednesday.

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.Discussion...
Lots of cloudiness and areas of showers continue across the
interior of NorCal early this morning despite the upper ridge
moving overhead. Temperatures early this morning are a little
cooler than 24 hours ago and range from the mid 30s to lower 40s
in the mountains to the upper 40s to mid 50s in the valley.

The threat for scattered showers will continue today as plenty of
low-level moisture lingers. Most of the showers are expected to
occur north of Interstate 80 where warm advection will be the
strongest. Snow levels will generally be around 6000-7000 feet.

Little change to timing or intensity of the next event Tuesday
into Thursday.
Precipitation moving through interior Northern California this
afternoon into this evening as another wave moves through the
area. Snow is falling in the Sierra with up to 6 inches possible
above 6000 ft. Extended the snow advisory into 10 pm this evening.
Precipitation will diminish Monday for areas south of the
Interstate 80 corridor as weak shortwave ridge builds into the
area ahead of the upper level low off the California coast. Some
lingering moisture and a weak disturbance may move across the far
north in the afternoon for a threat of showers on Monday north of
the I-80...especially over the mountains and Shasta County.

Precipitation spreads across the area again Tuesday as a closed
low off the coast approaches. Appears the system will tap into
deeper moisture ahead of it presently off the coast of Baja (TPW
forecast to be around an inch up into NorCal), and with strong
forcing we'll likely see some impressive precipitation generated
across the region. Showers and isolated/scattered thunderstorms
continue Tuesday night through Wednesday as the upper low moves
onshore. Gusty winds will also be possible at times.

Rainfall totals of an inch or two will be possible by Thursday in
the valley with up to 5 inches possible in some of the wetter
spots on the west slopes of the northern Sierra. The higher
elevations of the northern Sierra may see 12 to 18 inches of snow
along the crest, while the higher elevations of Lassen National
Park may see several feet of snowfall accumulation.

Main impacts from the storm will be possible travel delays across
the northern Sierra passes due to heavy snowfall along with wet
and slick roads at the lower elevations. Periods of moderate to
heavy rain over the burn scars left from the wildfires the past
few summers could lead to local debris flows.

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.Extended Discussion (Friday through Monday)...
A weak and splitting system near, to just inside, 130W on Friday
into Saturday warrants a slight chance to chance mention of
precip. The GFS is about 6 hrs faster than the EC bringing the
wave through north to central CA. However, the GEM cuts it off
offshore of SoCal. Weak ridging may hold on through Sunday,
followed by a more dynamic trough late Monday into Tuesday. Models
are hinting that the system early next week may give NorCal just
a glancing blow, with most of the dynamics remaining north of the
area. Daytime highs will be around 60 in the valley and 40s-50s in
the foothills/mountains with a partly to mostly cloudy sky. JClapp

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.Aviation...
An area of light rain to drizzle between highways 20 and 36 this
morning. Precipitation will continue to move east, mainly ending
between 14z and 17z.

The northern Sac Valley under MVFR with isold IFR cigs much of
today with IFR conditions in Delta and up west side of the Sac
Valley this morning. Patchy IFR/LIFR fog to potential develop
across portions of the Valley this morning toward sunrise.

For the mountains, widespread IFR/LIFR conditions will continue
through at least mid morning, becoming more isolated afterward.
JClapp

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.STO Watches/Warnings/Advisories...
winter storm watch from tuesday morning through late wednesday
night above 7000 feet in the west slope northern sierra nevada.

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