352
FXUS66 KSTO 182113
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
213 PM PDT Sun Oct 18 2026
For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.
.KEY MESSAGES...
- Gradual cool down begins Sunday with renewed precipitation
chances by the middle of next week.
- Onshore flow returns Sunday evening, providing temperature
relief and increased overnight/daytime humidity values
Monday through next week.
&&
.DISCUSSION...
...Rest of Today - Monday... Clear skies today with slightly
cooler temperatures. High temperatures this afternoon are on
track to be in the lower to mid 80s across the Valley floor, about
3 to 7 degrees lower than yesterday, with somewhat higher
humidity levels. An approaching Pacific Northwest shortwave trough
will bring increased onshore flow to the region by later this
afternoon into the evening, with a fairly strong Delta Breeze
gusting to 20 to 30 mph. Temperatures will be cooler tonight into
Monday morning and overnight humidity recoveries will increase
significantly, helping mitigate area fire weather concerns. Monday
the trough will develop into a closed low off the Northern
California coast. Daytime temperatures will be noticeably cooler
than seen recently, with Valley highs ranging from upper 60s to
low 70s over the Sacramento Valley and Delta, to the mid 70s in
the northern San Joaquin Valley. Breezy onshore flow continues
through the Delta into the evening, gusting to 30 mph, and over
the Sierra gusting to 35 mph. Generally dry weather is expected,
except for a slight chance of rain showers over the northern Coast
Range.
...Tuesday-Thursday...Confidence has increased in a cool,
unsettled pattern through the week. Ensembles continue to show
the low pressure drifting southward along the coastline Tuesday,
which may limit precipitation chances until the evening, with dry
weather during the day and widespread rainfall overnight. Moisture
will advect northward into the area on the east side of the low,
with best potential for precipitation south of I-80 Tuesday night.
Chances of precipitation continue Wednesday as the low opens into
a shortwave and tracks eastward through California. Instability
has trended higher, with a 20% probability of afternoon
thunderstorms now projected over the Sierra. General storm total
rainfall amounts range up to around 0.75" over the Sierra crest,
down to 0.05-0.20" in the Valley and lower foothills, though
confidence in specific amounts remains low, with model
fluctuations. Snow levels are expected to remain around 9,000
feet initially, limiting any snow to the highest peaks. Snow
levels drop to around 8,000-8,500 feet Wednesday night into
Thursday, which could bring some light accumulations to higher
Sierra passes, such as Sonora Pass and Ebbetts Pass, though even
there travel impacts should be minimal. Cooler temperatures,
higher humidity and precipitation will continue to decrease fire
weather concerns.
...Friday - Weekend...Friday is trending dryer as the shortwave
trough exits to the east, with just some light, lingering showers
over the Sierra and southern Cascades in the morning. A brief
period of eastern Pacific ridging should bring a shift to breezy
northerly winds through the day into early Saturday. Humidity
levels should remain relatively moist, limiting fire weather
concerns. Most of the clusters are suggesting a trough pattern for
the weekend, but range widely in the strength and location of it.
Overall continue to expect a continuation of cool, below normal
temperatures with unsettled weather. NBM is currently forecasting
widespread precipitation for Sunday.
&&
.AVIATION...
VFR conditions prevail across interior NorCal next 24 hours.
Surface wind gusts generally below 15 knots, except in Delta from
around 21z today through 18z Monday where onshore flow is forecast
to strengthen with west gusts up to 30 knots.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
