951
FXUS66 KSTO 271922
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
1222 PM PDT Thu Aug 27 2026
For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.
.KEY MESSAGES...
- Seasonably warm high temperatures continue today with a
cooling trend from Friday onward.
- Elevated Fire Weather conditions from dry conditions and
breezy winds through this evening for portions of the Valley
and foothills.
- Shower and isolated thunderstorm chances arrive late today
into Friday, generally from Interstate 80 southward.
- There is high uncertainty in exact details, but unsettled
weather and precipitation chances look to return by mid to
late next week.
&&
.DISCUSSION...
Today-Friday...
Despite clear to partly cloudy skies early today, a plume of
subtropical moisture is beginning to edge into interior NorCal
early this afternoon. While cloud cover is expected to become more
prevalent through the afternoon and evening hours, seasonably
warm temperatures and dry conditions look to persist for much of
the region north of Interstate 80 today. Resultant high
temperatures in the mid to upper 90s at low elevations and 80s at
higher elevations persist again this afternoon with breezy onshore
winds remaining strongest across the northern Sacramento
Valley/Burney Basin/northeast foothills this afternoon and
evening. As a result, Elevated Fire Weather conditions continue
for these locations through today.
As longwave troughing becomes a mainstay offshore of NorCal
through the end of the week, the aforementioned moisture plume
will have a direct conveyor toward the region today and Friday.
Given the broader nature of the forcing aloft today, primarily
showery activity is anticipated south of the I-80 corridor this
afternoon and evening, with likely little to no accumulating
precipitation. Available instability will remain the biggest
uncertainty with this event. Despite limited model agreement, with
clearing this morning and the advancing moisture plume aloft, a
few lightning strikes cannot be entirely ruled out in the northern
San Joaquin Valley and adjacent terrain later today.
Heading into Friday, the areal extent of subtropical moisture is
expected to become more widespread across interior NorCal. While
the primary shortwave feature is expected to track across the Pac
NW through the end of the week, a weaker, secondary midlevel
trough is on track to build into interior NorCal early Friday.
Available instability will likely be limited due to broader cloud
cover over the region, however, the presence of more appreciable
forcing aloft paired with more robust moisture may offset the
instability downturn. As a result, another day of showers and
isolated thunderstorms remains forecast for Friday. Highest
potential overall is still anticipated from I-80 southward with
best chances for thunderstorms (15-30%) remaining along the
Sierra. Similarly, probabilities for precipitation greater than
0.1" sit around 10-15% for the southern Sacramento and northern
San Joaquin Valleys with probabilities jumping to 40-70% for the
Sierra and adjacent upper foothills.
The Weekend Into Next Week...
As the moisture plume pushes eastward by the weekend, a trend
toward drier weather is anticipated area wide Sunday into early
next week. While chances are expected to be notably lower on
Saturday, there may be enough overlap of lingering moisture and
troughing aloft for additional shower/thunderstorm potential along
the Sierra south of Highway 50. At this time, probabilities of
showers and isolate thunderstorms sit around 10-15%, although
highest potential will likely be from the Sierra crest eastward.
Despite the broader drying trend that is on track late weekend
into early next week, the presence of a troughing aloft and low
heights will keep temperatures seasonable through the weekend.
By early next week, ensemble guidance is in general agreement on
a longwave trough deepening offshore of the Pac NW toward NorCal.
The immediate impacts of this developing pattern look to be even
further cooling to below normal temperatures alongside breezier
onshore winds. Heading toward the middle of next week, there are
some indications within ensemble guidance for a return to
unsettled and active weather. These indications are predicated
upon the potential for remnant tropical moisture to become swept
up in the deepening trough and yield additional
shower/thunderstorm chances to the region. There are stark
discrepancies regarding the timing and location of this additional
moisture plume though leading to notably high uncertainty toward
the end of the extended forecast period at this time.
&&
.AVIATION...
VFR conditions prevail across interior NorCal with surface winds
generally below 12 kts. A weather system will arrive later
tonight, introducing VCSH to northern San Joaquin TAF sites around
02z Friday through 10z. If any shower develops, MVFR conditions
will be possible.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
