Area Forecast Discussion
Issued by NWS Sacramento, CA

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469
FXUS66 KSTO 151650
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
850 AM 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 approaches the PacNW. Associated baroclinic cirrus
spreading over Interior NorCal. Some patchy mist in the Southern
Sacramento and Northern San Joaquin Valleys is producing local
MVFR visibilities this morning. Visibilities will increase
over the next couple hours. Mid to high level cloudiness will be
on the increase today as the wave approaches. Cooler temperatures
will result with low to mid 60s in the Central Valley and 40s to
low 60s for the mountains and foothills.

Short wave trough digs through Interior NorCal tonight. System
looks weak with limited available moisture, but models suggest the
potential for a few light showers over the Shasta and Plumas
mountains, and possibly higher elevations of the Northern Sierra
Nevada. QPF looks light, less than a tenth of an inch with little
to no snow accumulations 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)
Models continue in agreement with a cold Pacific storm system
dropping south mid-week. This system breaks down the ridge rather
rapidly and brings a few impulses of precipitation across Northern
California. Current forecast reflects precip chances Wed-Thur
with possible pattern change. This system appears to be rather dry
with only light rain and snow amounts expected. Relatively low
confidence remains with specific system details.

&&

.AVIATION...

VFR/MVFR conditions across interior NorCal the next 24 hours
except local MVFR conditions in BR for the southern Sacramento
and northern San Joaquin Valleys. Valley winds generally below 10
knots.

Shoe/Dang

&&

.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 4 PM PST Saturday for Carquinez
Strait and Delta-Central Sacramento Valley-Clear Lake/Southern
Lake County-Mountains Southwestern Shasta County to Northern
Lake County-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley-Northern San Joaquin Valley-Southern
Sacramento Valley.

&&

$$



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