000
FXUS66 KSTO 272032
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
132 PM PDT Wed Sep 27 2023

.Synopsis...
Dry weather through Thursday, then showers Friday PM through
Sunday. Below normal high temperatures with periods of locally
gusty winds this evening through tomorrow.

&&

.Discussion...
Dry conditions continue today with below normal temperatures set
to continue through the week. Winds are set to increase and turn
northerly-northeasterly this evening across the Northern
Sacramento Valley and along I-5 and can expect lowered humidity
values this afternoon through Thursday afternoon. However, this is
not anticipated to result in any critical fire weather conditions
or wind advisory criteria. EC Ensemble Meteograms show max wind
gusts around 25 mph at Redding Thursday and NBM forecasting
humidity values in the upper teens and low 20s. With rain incoming
later this week, humidity values are expected to have good
recovery after this event into the weekend.

An amplifying ridge through the Pacific as high pressure
strengthens will aid in longwave troughing moving over the Pacific
Northwest through California on Friday morning. From this, rain
chances increase Friday afternoon across the Northern Sacramento
Valley and Sierra and persisting over the Sierra through Sunday
afternoon. Latest WPC rain totals for Friday through Sunday are
0.25-0.80" with up to around an inch possible across the Sierra
and less than a tenth for the Northern Sacramento Valley. Heaviest
rainfall will be across the Sierra Saturday morning with lingering
rain showers Sunday. Convective potential will be limited through
the event, but current NBM forecast does show a 10-20% chance of
possible thunderstorms north of I-80 to Redding Friday late
evening and Saturday afternoon. Highest elevations across the
Sierra continue the possibility of light snow this weekend.

Onshore flow increases as the aforementioned trough moves through
Central CA, so south to west wind gusts increase across the Valley
and Sierra to 15-20 mph with stronger gusts across high terrain
Friday afternoon.

&&
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...

Ensemble and cluster analysis remain confident of an upper-level
low digging into Northern California on Sunday and translating
slowly east on Monday. A slight western nudge to the location of
the aforementioned low on the latest ECMWF and GFS ensemble runs
has led to increased PoP and PoT chances for the Sierra and
adjacent foothills, mainly south of Donner Pass. Current NBM
projections are showing a 15-30% PoP for the foothills and 40-60%
PoP for the Sierra Sunday afternoon and evening. Temperatures will
be in the mid to upper 70s for most of the CWA, with cooler
temperatures (50-65) for higher elevations. Winds will transition
to a more northerly component Sunday, but fire weather conditions
will remain below critical thanks to RH values being 30-50 range
from associated moisture with the low.

Moving into Monday and Tuesday, the low will propagate eastward
and meander near the Arizona-Nevada-California border, and an
upper level ridge will develop in the PacNW, effectively placing
our area in an Omega pattern. We will still be under the influence
of subtle troughing from the east, so there will be an isolated
(10%) chance for showers/storms over the higher elevations in the
Sierra, as leftover moisture wraps around the weakening low to our
east. Thanks to the ridging to our west, temperatures will begin
to recover and return to the mid to upper 80s for the Valley, and
70s for the Sierra and Coastal Range. Dry and quiet weather is
expected for the remainder of the extended period.

//Wood

&&

.AVIATION...
VFR conditions over interior NorCal next 24 hrs. Surface winds
generally below 12 kts except vicinity of Delta southwesterly
winds up to 20 kts after 03z. In Northern and Western Sac Valley,
area northerly surface wind 10 kts with up to 20 kt gusts after
07z Thu.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$