Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 222200
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
300 PM PDT Fri Sep 22 2017

.SYNOPSIS...

Unseasonably cool weather system will bring mountain rain and
snow showers this afternoon and evening. Another inch of snow is
possible at high elevations south of highway 50. Turning warmer
and drier from this weekend into next week.

&&

.DISCUSSION (Today THROUGH Monday)...

Water vapor and model analysis continues to show a large scale
high amplitude trough centered over the Great Basin which brought
northern California below normal temperatures and mountain
precipitation for the past several days. Little embedded shortwave
troughs within the main flow as the low rotates were bringing
scattered returns on radar of showers with increased cloud cover
over the mountains. Temperatures across the region little changed
compared to 24 hours ago ranging from the upper 60s to lower 70s
across the valley and in the upper 40s to lower 50s for the higher
elevations.

Main sensible weather will be associated with the rotating upper
level low pressure system over the Great Basin as little embedded
shortwave troughs push through the mountains this afternoon. In
combination with available atmospheric moisture, rain and snow
showers above 6000 feet are possible again this afternoon into the
evening hours. An additional inch of snow can be expected for the
highest elevations, but some isolated locations could possibly see
up to an inch in convective snow squalls. The main area of lift
will occur along and south of I-80 in the mountains.

Upper level disturbance will continue to slide eastward as an
upper level ridge builds into the eastern Pacific. This stable air
mass will bring a return of near to slightly above normal
temperatures and dry sunny weather to northern California. High
temperatures can be expected to reach the upper 80s to lower 90s
in the valley by Monday and 50s/60s for higher elevations.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Warm and dry weather dominates in the extended period as upper
level ridging continues to build over the area. Temperatures
across interior NorCal will range from 5 to 10 degrees above
seasonal normals through Friday. Valley highs will reach the low
90s by Tuesday and will remain steady through at least the end of
the week. The foothill and mountain high temperatures will range
from the 60s to the 80s. Gusty northerly winds continue through
Tuesday. These will continue to dry and warm the area creating an
elevated fire risk. HEC

&&

.AVIATION...

VFR conditions expected for Valley TAF sites for the next 24
hours with scattered mid level clouds. Scattered
mountain/foothill rain showers today and isolated afternoon
thunderstorms over the Sierra south of Lake Tahoe. Snow showers
are possible above 6000 feet in the Sierra through the evening.
Northerly winds expected to develop this afternoon around 5 to 10
kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Sunday afternoon through late Monday
night for Carquinez Strait and Delta-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
Motherlode From 1000 to 3000 Ft. Includes portions of Nevada-
Yuba-Placer-Amador and ElDorado Units-Northern Sacramento Valley
to Southern Tehama County Line Below 1000 Ft-Northern Sierra
Foothills from 1000 to 3000 Ft. Includes portions of Shasta-
Trinity and Butte Units-Northern Sierra Including Lassen NP and
Plumas and Lassen NF/S West of the Sierra Crest (West of Evans
Peak-Grizzly Peak-Beckworth Peak)-Northern Sierra Including the
Tahoe and ElDorado NF/S West of the Sierra Crest-Southeast Edge
Shasta-Trinity NF and Western Portions of Tehama-Glenn Unit-
Southern Motherlode From 1000 to 3000 Ft. Includes portions of
Calaveras-Tuolumne Unit-Southern Sacramento Valley in Yolo-
Sacramento Far Western Placer, southern Sutter and Solano County
Below 1000 Ft-Stanislaus NF West of the Sierra Crest.

&&

$$



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