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Area forecast discussion
National Weather Service Sacramento California
430 am PST Tue Jan 23 2018

Synopsis...
fair today with some patchy morning valley fog and drizzle.
Stronger Pacific storm impacts the area Wednesday into Friday
with periods of moderate to heavy Rain, Mountain snow and gusty
wind. Drier weather over the weekend.

&&

Discussion...
satellite imagery showing plenty of low clouds and patchy fog
still lingering across much of the Central Valley, and in the
mountain valleys, while the remainder of interior norcal is
seeing mainly clear skies other than some high clouds beginning to
spread onshore ahead of the mid-week weather system. The depth of
the stratus layer over the Sacramento region has decreased
overnight as the subsidence inversion has strengthened, so
probably little if any drizzle expected this morning.

Dry weather today, with milder temperatures for most areas, under
upper level ridging.

Little change to current forecast other than to slightly slow
down the onset of precipitation across interior norcal on
Wednesday. Still appears a more impactful system will affect the
region mainly Wednesday and Thursday with a good shot of
precipitation, heavy mountain snow with lowering snow levels, and
gusty winds.

Heavy snow expected in the mountains of western Plumas and
northern Sierra Nevada Wednesday night into Thursday and have a
Winter Storm Watch in effect. Several feet of snow is possible
over the highest elevations. As snow levels lower significantly
behind the front Wednesday night and Thursday, accumulating snow
in the coastal and Shasta mountains may warrant additional winter
weather products. Could also see some light accumulations in the
upper elevations of the NE foothills and motherlode Thursday.

Unsettled weather continues Thursday as Post frontal upper
troughing moves through. Models showing limited cape attm
Thursday, but trending up. With steepening lapse rates Thursday
afternoon as 500 mb temps cool into the lower -30s deg c, will need
to continue to monitor for potential thunderstorm activity. Storm
total liquid quantitative precipitation forecast for this system ranges from about a 1/3" to 1.5"
in the Central Valley (highest in the northern Sacramento
valley) with 1 to 3 inches for the foothills and mountains.

&&
Extended discussion (saturday through tuesday)




Jet stream and associated moisture will be draped across northern
California Saturday as upper level heights rise with building
ridge and push unsettled weather northward and out of the forecast
area. The northern Sacramento Valley and northern mountains can
expect chances for rain and light mountain snow accumulations
Saturday and Saturday night. High pressure dominates Sunday and
brings a return to dry conditions before the next weather
disturbance moves inland for the beginning of the next workweek.
High temperatures through the extended forecast period will be
near to slightly above average for January.

&&

Aviation...




VFR conditions expected for the northern Sacramento Valley
terminals with MVFR/IFR conditions for Delta influenced locations.
Expecting conditions to improve this afternoon before another
round of lower ceilings/visibilities tonight as the next weather
disturbance approaches. Precipitation expected to begin 18z
Tuesday through 00z Wednesday.
&&

Sto watches/warnings/advisories...
Winter Storm Watch from Wednesday afternoon through Friday
morning for West Slope northern Sierra Nevada-western Plumas

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