Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 281037

337 AM PDT FRI AUG 28 2015

Dry weather today with daytime highs just a bit lower than
Thursday under increasing cloud cover. Cooler temperatures
beginning over the weekend with a chance of showers over the
northern portion of the state Saturday. Dry with a little below
normal daytime high temperatures continuing through most of next


High clouds spilling into the northern CWA this morning as a low
pressure system over the Eastern Pacific edges towards the coast.
The overall airmass is not much different today than Thursday but
increasing cloud cover should help cool things just a bit. A
slightly increased delta breeze will help cool temperatures a bit
more in delta influence areas. High temperatures today are likely
to remain a little above normal but valley temperatures should
remain under the triple digit mark. An early season Pacific
frontal system will be moving into the Pacific Northwest and
norcal late tonight and early Saturday or about 6 hours later than
forecast by models 24 hours ago. The blended TPW product still
shows an impressive moisture plume exceeding 1 and a half inches
feeding into this system. Weak dynamics and instability should
however keep precipitation over the forecast area to a minimum and
mainly to the north of the Sacramento area. Redding QPF for
example varies from a couple of hundredths to a couple tenths of
an inch. Cloud cover and airmass cooling will bring a significant
cooling on Saturday with high temperatures dropping by at least 10
degrees most areas. Surface gradients with this system are not
particularly tight but the upper elevations will likely see at
least a short period of breezy to gusty winds as the front passes
through. Model timing shifts the frontal boundary into the
Cascades Saturday afternoon but a couple models show a secondary
disturbance moving into the Sierra Saturday evening. Have
therefore added a slight threat of showers Saturday evening there.
A lingering trough remains over the west coast on Sunday keeping
daytime highs below normal although clearer skies should allow for
a slight warming. Fair skies and a bit more warming are expected
on Monday but troughing over the west coast should keep daytime
highs a little below season norms.


A broad trough pattern will persist over NorCal through the
extended forecast. In general, interior NorCal will experience
cooler than average weather, but there is currently low confidence
that any rain will impact our region. Daytime highs from Tuesday
through Friday will range 2-12 degrees below normal. It looks
like Wednesday and Thursday will be the coolest days: valley highs
will be in upper 70s to upper 80s and mountain highs will range
about 60-80 degrees.

The trough appears to deepen southward towards the end of the week
and the ECWMF hints at some precipitation working its way into
portions of NorCal on Friday, but the GFS stays dry. With low
confidence in rain, have kept the forecast dry for the extended
period.  JBB



VFR conditions continue for TAF sites. Winds will be light this
morning, under 10 kts. However, winds will pick up this afternoon
and evening as a trough moves inland and enhances
southwesterly/onshore flow into our region. Generally, after
21-22Z, TAF sites will see sustained winds 10-15 kts with gusts up
to 20 kts. Delta breeze will also be enhanced this afternoon and
overnight with sustained winds 15-20 kts and gusts up to 30 kts.
Southwesterly gusts over the mountains 20-30 kts.  JBB



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