Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 032147

247 PM PDT THU SEP 3 2015

Below average temperatures through Saturday as a weather system
impacts the region. Showers and thunderstorms possible across the
northern portion of the state Friday into Saturday morning with a
dusting of snow over Lassen Peak, followed by some breezy
offshore winds this weekend. Warmer weather returns Sunday into
next week.


.Discussion (Tonight through Sunday)...
The axis of an approaching upper trough has maintained it`s
general position near the NorCal coast today and will slowly
track across Northern CA through Saturday. This will bring cooler
than normal weather along with the possibility of showers and
thunderstorms. Onshore flow will continue as the trough approaches.

Tomorrow, the trough will deepen into NorCal bringing a colder
airmass causing Friday to be the coolest day in the forecast.
Valley highs will be in the upper 70s to low 80s...a good 8 to 15
degrees below normal. The air will become more unstable on Friday
while also bringing possible precipitation to portions of NorCal
north of Interstate 80. Precipitation should start in Shasta
County late morning then spread southward through the day with
best chances in higher terrain. CAPE & Modified Total Totals
indicate that the most unstable period will be Friday afternoon
and overnight. Potential thunderstorm development is favored in
the afternoon and early evening over the northern mountains, while
showers may continue into early Saturday. Snow levels will also
lower between 7000 to 8000 ft so the Lassen Park area could see a
dusting of snow. West to southwest winds will be breezy as the
trough moves across our region on Friday...especially through the
Delta and over the mountains.

The trough passes Saturday morning which will increase the
north/south surface pressure gradient Saturday morning through
Sunday. In turn, this will generate breezy north/northeast winds,
especially down the west side of the valley and the lower west
slopes of the Sierra.     JBB/JClapp

.Extending Discussion (Monday THROUGH Thursday)
Dry conditions through the extended forecast ridge
gradually builds over California. Temperatures will warm to
slightly above normal levels.


Upper low over B.C. digs south along west coast with westerly
flow which means onshore sfc and boundary layer winds...gusts to
25 kts through Delta and over higher terrain this evening. VFR
conditions over interior NorCal next 24 hrs, except local MVFR
cigs in showers over Shasta mountains after 12z Fri. JClapp



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