Area Forecast Discussion
Issued by NWS Sacramento, CA

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776
FXUS66 KSTO 201117
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
317 AM PST Fri Jan 20 2017


.Synopsis...
Next in series of winter storms moves through Norcal today
bringing rain, mountain snow and strong winds. Showers Saturday
followed by a slightly stronger system Sunday into Monday. With
these storms, expect mountain travel impacts due to snow and
winds and moderate to heavy rain at the lower elevations with
windy conditions. Winds could become damaging at times. Should see
extended dry period for the middle to end of next week.

&&
.Discussion...
Pacific frontal band appears to be moving on to the coast at this
time with post frontal showers and isolated thunderstorms being
detected off the coast. At this time, nearly all of the CWA is
seeing light warm sector precipitation. MFR to SAC surface
gradient over 10 mb this morning with the northern Sacramento
valley seeing sustained winds topping 20 mph. These winds will
shift southward as the front moves inland so have left up wind
advisory for the valley. Moderate snow falling over the Sierra at
this time with breezy winds so winter storm warning still looks
good there. Current forecasts give 2 to 3 feet of new snow between
now and Saturday morning. Snow levels across the northern
mountains appear to be around 3000 to 3500 feet. This may make for
some slick roads that rise to that elevation so have left snow
advisory for northern mountains and coast range up as well. QPF
with this system not high enough to expect significant areal
flooding but local flooding remains a possibility. Frontal passage
through the Sacramento area expected later this morning with
decreasing winds by mid day. New weather concern then becomes
afternoon thunderstorms with projected instability behind the
front for thunderstorm threat in the valley. This threat will
continue through early this evening but should end by late evening
as upper trough shifts east of the region. Weak ridging slides
over the state Saturday but plenty of moisture continues to slide
over the ridge so showers will continue Saturday.

Although QPF drops significantly tonight...orographics keep
snowfall going over the west slopes of the Sierra Cascade range.
This break is relatively short with next strong frontal band
moving into the state late Saturday night. This brings another
round of rain and mountain snow with significant ramp up in snow
over the Sierra. Since the slowdown in Sierra snowfall Saturday
afternoon and evening is so short...have extended the winter
storm warning for the Sierra Cascade range to include the Sunday
storm. This storm, which is forecast to move through Norcal
through the day on Sunday will bring another round of heavy
precipitation, mountain snow and possibly even stronger wind than
todays storm. Not sure yet about thunderstorm potential Sunday
afternoon as the brunt of the storm may still be crossing the
valley during the max heating part of the day. This system passes
east of the CWA by late Sunday night but showers continue on
Monday with models consistent in dropping a cold low down the
coast. If this scenario pans out then valley thunderstorms are
likely to return during the day Monday.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Extended period of dry weather expected across the region during
the extended forecast period as models continue to show strong
ridging developing along the West Coast. Cool nights and mild
days with this dry pattern.
&&

.AVIATION...

Widespread MVFR with areas IFR next 24 hours as strong Pacific
frontal system moves through the area. Southerly winds 15-25 kts
gusts 35-45 kts, gradually decreasing after 20Z. Snow levels
030-040.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 4 AM PST Monday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

Winter Weather Advisory until 4 PM PST this afternoon for
Mountains Southwestern Shasta County to Northern Lake County-
Shasta Lake Area / Northern Shasta County.

Wind Advisory until 1 PM PST this afternoon for Carquinez Strait
and Delta-Central Sacramento Valley-Motherlode-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.

&&

$$



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