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Area forecast discussion
National Weather Service Sacramento California
1050 am PST Tue Dec 10 2019

Synopsis...
quiet weather today with areas of morning valley fog and near
average temperatures. Rain chances return to the region tonight
with more widespread precipitation expected late in the week.

&&

Discussion...
the morning update: visibilities have improved as dense fog near the
I-5 and Hwy 99 corridor from the SAC vicinity to sck and moderate has now
lifted into the proverbial low gray cloud deck. Much of the low
cloud deck may persist throughout the day, lifting this evening when
the frontal system moves into the region, spreading light rain over
much of our County Warning Area late this afternoon and evening. Radar echoes
showing up along the nrn California coast at press time. Timing of the upper
trof suggests the precip should end by Wed morning as the trof moves
through our region. Behind the trof, heights rebuild on Wed as a
ridge axis slides into the region. Some light sprinkles/showers are
still possible mainly in the nrn part of our County Warning Area on Wed, where
warm-advection may allow for some lingering light precipitation.
Jhm

Previous discussion...
the upper ridge that brought the dry weather to the region on Monday
is moving east as the next upstream short-wave trough approaches.
Satellite imagery shows high clouds out ahead of the system already
moving over norcal.

Fog has been developing in the southern half of the Sacramento
Valley southward into the northern San Joaquin Valley since late
Monday evening. So far, the most extensive dense fog has been in
the Sacramento area with patches of dense fog in around Modesto
and across portions of the motherlode. The extensive high clouds
may limit further spread of dense fog, and forecast soundings
indicate it may lift to a low stratus deck this morning.

Dry weather will persist today, but a brief period of light
precipitation is expected across norcal tonight as the short-wave
and a shot of warm-advection move through interacting with tpw of
around 3/4 to 1 inch over the area. Quantitative precipitation forecast of less than a tenth of
an inch is likely in the valley, with less than a third of an inch
over the mountains. An inch or two of snowfall accumulation will
be possible above 5500-6000 feet.

Ridging in the wake of tonight's wave gradually flattens the
remainder of the week as strong mid/upper level jet across the
eastern Pacific reaches the West Coast. Most of the forecast area
is expected to see dry weather Wednesday, except across the
mountains north of Redding where warm-advection may allow for some
lingering light precipitation.

Light precipitation is then forecast to increase again along a
stalled out front by Thursday as warm-advection ramps up and
deeper moisture spreads into the region. The front may sag far
enough south later Thursday into Friday to allow light
precipitation to spread across the Sacramento region and into the
I-80 corridor over the northern Sierra. Snow levels will be above
8k ft limiting winter travel impacts.

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Extended discussion (saturday through tuesday)...
fairly zonal upper level flow is expected to remain over norcal
Saturday. Weak shortwave along the flow will bring a chance of
light showers to the area Friday night through Saturday. Another 3
to 6 inches of snow accumulation is possible Saturday mainly for
elevations above 5000 feet, though dropping snow levels early
Saturday could bring light accumulation down to 4000 to 4500 feet.
This could cause some travel issues over mountain passes
Saturday.

Zonal flow breaks down behind this weather system as upper level
ridging builds over the area Sunday into Monday, bring dry
weather back to interior norcal. Ensembles hinting at wetter
weather system impacting the West Coast beginning Tuesday. However
confidence is low at this time, so keep an eye out for forecast
updates. Hec

&&

Aviation...
IFR/LIFR visibilities across the Central Valley due to fog
through 18-21z, generally areas Marysville and south. Otherwise,
VFR visibilities and winds generally less than 10 kts.

&&

Sto watches/warnings/advisories...none.

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