Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 031108

408 AM PDT SAT OCT 3 2015

A vigorous low pressure system will bring cooler weather, windy
conditions, and a chance of showers and thunderstorms this
weekend. Showers will linger into Monday over the Sierra Nevada
south of Highway 50.


.DISCUSSION (Today through Tuesday)...
Upper level low over Washington state early this morning is
progged to dig rapidly southward into Socal through Sun. The low
is forecast to deepen as it drops southward with the digging polar
jet. The continentality of the developing/deepening system means a
rather dry system...but dynamics are very strong and will squeeze
out some precip mainly over the west slope of the Sierra Nevada.
The valley may see some light showers/sprinkles. Pressure falls
ahead of the deepening system and then rapid pressure rises behind
it will result in increasing winds. Initially from the south to
southwest ahead of the system through the Carquinez Strait and
into the valley...but more so from the north and east as the
strong upper low and associated cold front drop southward rapidly
over Norcal late this afternoon and tonight.

About a 9 mbs SAC-MFR gradient is forecast by this afternoon,
tightening to about 12-13 mbs this evening mainly N of the I-80
corridor. Highly anomalous north to east wind speeds are forecast
in the Nrn half of the Sac Vly and adjacent Sierra Nevada at 850
mbs (~5000ft MSL), respectively. These winds will transfer to the
Coastal Range as well. Due to the forecast 925 mbs winds, we have
issued a wind advisory in the area of the tightest pressure
gradient from the northern/central Sac Valley and the Coastal
Range Sat afternoon/evening...while the 850 mb anomaly suggests
windy ridge winds over the Nrn mtns and west slope of the Sierra
(northward of Highway 20) tonight into early Sun. The 850mb wind
anomal is up over -9, which has a 30 year return interval. Even
though have issued a wind advisory, the potential exists for the
Coastal Range and west slope of Sierra to be upgraded to a High
Wind warning. Right we have gusts in the 40s and 50s over the

Showers may linger over the Sierra south of Highway 50 on Monday
due to wraparound moisture from the Low over southern NV/southeast
CA area. Ridging builds in with gradually increasing temperatures
and dry conditions as the Low weakens and moves eastward.

.EXTENDED DISCUSSION (Wednesday through Saturday)
Upper level high pressure ridging expected to remain over the
western U.S through the extended period. Genreally light winds are
expected through this time. Daytime highs Wednesday are forecast
to come in near to a little above normal. Temperatures will warm
slightly each day reaching several degrees above normal by next


Upper low dropping southward through northern California over
next 24 hours. A few light showers possible this evening and over
night with best chances Sacramento southward. VFR conditons
expected next 24 horus with ceilings above 50k feet. Winds
increasing this afternoon over the Sacrametno valley...coastal
mountains and southern Cascades. North to northeast wind gusts
over 40 mph possible. &&

WIND ADVISORY from 5 PM this afternoon to 11 AM PDT Sunday for
Central Sacramento Valley-Clear Lake/Southern Lake County-
Mountains Southwestern Shasta County to Northern Lake County-
Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-
Shasta Lake Area / Northern Shasta County-Western Plumas
County/Lassen Park.

RED FLAG WARNING from 5 PM this afternoon to 11 AM PDT Sunday
for Central Sacramento Valley in Glenn, Colusa, Yuba, Northern
Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-
Eastern Portion of Shasta/Trinity NF-Lake County Portion of Lake-
Napa-Sonoma Unit-Northern Sacramento Valley to Southern Tehama
County Line Below 1000 Ft-Southeast Edge Shasta-Trinity NF and
Western Portions of Tehama-Glenn Unit-Southern Sacramento Valley
in Yolo-Sacramento Far Western Placer, southern Sutter and
Solano County Below 1000 Ft.


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