Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 262200

Area Forecast Discussion
National Weather Service Sacramento CA
300 PM PDT Tue Oct 26 2021

Quieter weather building in. Light showers possible through early
tomorrow morning. Dry into the end of the week with shower chances
Friday into Saturday in far northern California.


Light returns are noted on radar early this afternoon with only
measurable precipitation being seen in the foothills and mountains
north of I-80, and perhaps the city of Redding. Some breezier winds
are noted in the northern and central Sacramento Valley with gusts
generally up to 25 mph. Otherwise, mid and low level clouds are
still streaming across much of the area bringing cooler than normal
highs to all of interior Northern California this afternoon.

Showers may continue tonight into early tomorrow morning mainly
across the same area as precipitation was seen today. Snow levels
are already on the rise this afternoon and additional snow
accumulation over the mountains is not expected overnight. Sky cover
begins to decrease tomorrow morning as ridging continues to build in
over the area with a noticeable warm up of about 8 to 12 degrees seen
compared to today. Near seasonable temperatures and dry weather
expected into late week. Valley fog may be possible in the mornings.
Ridging begins to break down slightly on Friday as a shortwave may
form and bring chances for additional rain to far northern
California beginning Friday evening.


Upper ridge over Norcal begins to weaken on Fri in advance of a
closing mid-level low pressure center. Differences in the track of
the low center provide a great deal of uncertainty in the areal
coverage of PoPs/QPFs mainly on Sat. (GFS is farther south than
the ECMWF which would virtually warrant PoPs for most, if not all,
our CWA.) With the 5H cluster analysis showing a trof over Norcal
and a weakness region in the 5H field over OR, we believe the
closed low will take a Nly track per the ECMWF. With cyclonic
flow south of the closed low over Norcal some light rain is
forecast mainly over our Nrn zones. Forecast water vapor transport
shows Norcal in between moisture plumes so just light QPFs are
expected over the Nrn mountain zones. A narrow highly amplified
ridge builds along the W Coast on Sun behind the filling/exiting
upper low as it phases with the deep/cold Canadian trof carved out
by a lobe of Arctic air rapidly descending over central Canada
from just south of the N pole. The dry weather for Norcal on Sun
won`t last long as the next Pacific front is forecast to move
inland on Mon bringing another round of light showers. This system
exits our area by Tue with dry weather returning. Below normal
max temps forecast through the EFP. JHM



VFR conditions at Valley TAF sites south of KRBL, otherwise mostly
MVFR conditions in scattered light showers over the Nrn terminal
locations and over Sierra through about 18z Wed. Mid-level cloud
deck mostly 5-10 KFT over Srn terminal locations expected to
persist into evening. Chance of stratus/fog developing over Nrn
San Joaquin Valley around sunrise Wed with local IFR/LIFR conditions
in BR/FG as mid-level cloud deck shifts Nwd and skies clear.




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