Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 152315
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
315 PM PST Fri Dec 15 2017



.Synopsis...
Weak system brings a slight chance of light showers over the
northern mountains this afternoon into tonight, otherwise dry
through early next week. Breezy to windy conditions forecast this
weekend, resulting in increased fire potential.

&&

.Discussion (Today through Monday)...
Upper ridging along the West Coast being squashed as short wave
trough progresses. Clouds are increasing over Interior NorCal,
with ceilings lowering, as cold front approaches. System moves
through tonight however dynamics are weak and available moisture
is limited. Models continue to show a few light showers possible
over the Shasta and Plumas mountains, and possibly higher
elevations of the Northern Sierra Nevada. QPF is less than a
tenth of an inch with little to no snow accumulation expected.

Surface and upper ridging builds back inland behind this wave
late tonight into early Saturday. Strong pressure gradients
develop overnight, leading to breezy to windy conditions across
Interior NorCal Saturday. Latest model guidance is suggesting
wind speeds into advisory criteria Saturday across portions of the
Central Valley, especially over the western half extending into
the Coastal Range. Gusty wind will lower humidities, and with dry
fuels already in place, there will be increased fire potential.
Red Flag Warning and Wind Advisories are in effect. Synoptic
cooling on Saturday will result in highs in the upper 50s to lower
60s for the Central Valley with 30s to 50s for the mountains and
foothills.

Breezy conditions continue Sunday, but wind speeds and pressure
gradients look to be less. Winds will generally be light Monday as
heights and temperatures slowly trend up.

PCH

&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Confindence is improving that a cold upper trough from the Gulf
of Alaska will drop down through the region on Wednesday, bring
the potential for precipitation to most of the area. This trough
has trended a little deeper and wetter, though this is not
expected to be a very wet system. Up to around a third of an inch
of liquid equivalent is expected in the mountains, up to around a
tenth of an inch in the Valley. Snow levels will drop quickly
behind a strong cold front Wednesday afternoon, down to around
3500 feet over the southern Cascades, 5000 feet in the Sierra.
Snow amounts of 1 to 3 inches are currently projected by Wednesday
evening. Drier weather returns by Thursday and continues into the
weekend.

Temperatures cool from Wednesday on, with Valley and foothill
highs generally remaining in the 50s, morning lows in the 30s. EK


&&

.AVIATION...


VFR conditions across interior NorCal over the next 24 hours
except local MVFR in BR for the southern Sacramento and northern
San Joaquin Valleys. Valley northerly winds generally below 10
knots this evening, increasing to 22 kt by around 18z, with gusts
to 40 kt. An Airport Weather Warning is in effect for SCK, with
sustained winds 20 to 30 kt in the afternoon. The northerly winds
will inhibit fog formation, but morning BR is possible. EK


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 10 PM this evening to 10 AM PST Sunday for
Carquinez Strait and Delta-Central Sacramento Valley in Glenn,
Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-
Eastern Mendocino NF-Lake County Portion of Lake-Napa-Sonoma
Unit-Northern San Joaquin Valley in San Joaquin and Stanislaus
Counties 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.

Wind Advisory from 4 AM to 6 PM PST Saturday for Carquinez
Strait and Delta-Central Sacramento Valley-Clear Lake/Southern
Lake County-Mountains Southwestern Shasta County to Northern
Lake County-Northern Sacramento Valley-Northern San Joaquin
Valley-Southern Sacramento Valley.

&&

$$



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