Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 031650
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
950 AM 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,
followed by some breezy offshore winds this weekend. Warmer
weather returns Sunday into next week.
The axis of an approaching low pressure trough is centered near
the NorCal coast this morning and will slowly track across
Northern CA now through Saturday (this upper low hasn`t done
anything fast). This will bring cooler than normal weather along
with the possibility of showers and thunderstorms. Onshore flow
will continue as the trough approaches so highs today will be in
the low 80s for much of the valley, 70s in the Delta, 60s to mid
70s in higher terrain.
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 towards Interstate 80
through the day with best chances in higher terrain. CAPE &
Modified Total Totals indices indicate that the most unstable
period will be Friday between about noon into late evening which
is when thunderstorm development will be favored over the northern
mountains. 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
.EXTENDED DISCUSSION (Monday THROUGH Thursday)
Another short wave trough moves through longwave Monday across
far northern portions of California. Models differ with strength
of the wave with oper GFS strongest and EC weakest. Overall
dynamics and moisture however look limited and expect main impact
for the area will be some locally breezy wind over higher terrain.
Upper ridging from the EPAC progged to gradually build over NorCal
Tuesday into Thursday resulting in dry weather with high
temperatures rising to slightly above normal.
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 afternoon and
evening. VFR conditions over interior NorCal next 24 hrs, except
local MVFR cigs in showers over Shasta mountains aft 12z Fri.