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000 FXUS66 KSTO 131916 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 1216 PM PDT Sun Sep 13 2026For additional details on weather and expected impacts over the next 7 days, please visit weather.gov/sto/briefing.KEY MESSAGES
- Critical fire weather conditions through Monday late afternoon due to gusty winds and low daytime humidity
- Red Flag Warning in place for portions of the Sacramento Valley and adjacent foothills until 5 PM PDT Monday
- Cooler, below normal temperatures today. Warming trend Monday onward with Valley highs in the mid 80s to low 90s.
DISCUSSION
Today-Monday: Clear and sunny skies are being observed today across interior Northern California. Temperatures are trending 10 to 15 degrees below normal today, with forecast Valley highs in the mid to low 80s and temperatures in the 60s and 70s across the foothills and mountains.
Today into Monday, an upper low will continue to pass through the Pacific Northwest resulting in breezy to gusty north winds through the Sacramento Valley and downsloping winds along the western slopes of the Sierra. North winds are just beginning to increase through the northern Sac Valley and northern San Joaquin Valley with gusts to 20 mph being observed as of 12PM. North winds will continue to increase as the day goes on, peaking early Monday morning and into midday. Maximum gusts are forecast to be 25 to 35 mph, with the strongest winds located along and west of the Interstate 5 corridor. These drying north winds will also keep daytime humidities in the teens to low 20s, possibly even the single digits on Monday. As a result, periods of critical fire weather conditions are expected and a Red Flag Warning remains in effect until 5 PM Monday for portions of the Sacramento Valley and adjacent foothills.
Gusty north winds will continue through the late afternoon on Monday, before gradually weakening. Current probabilities advertise a 30 to 40% probability of gusts greater than 35 mph.
Temperatures are also forecast to jump several degrees on Monday with Valley locations seeing high temperatures in the mid 80s to low 90s.
Tuesday-Saturday: Weak troughing is forecast to remain over NorCal bringing in period of breezy onshore flow. Humidities will remain low on Tuesday as a result of the north winds, with moderate overnight recoveries Monday night into Tuesday, which may bring locally elevated fire weather conditions. Seasonable temperatures will persist through this week, with a brief cool down midweek before warming into the weekend. Models depict an upper low dropping into Northern California around the midweek period which may bring chances for isolated thunderstorms around the northern fringes and mountains of Shasta County, however current guidance keeps any activity further north and there is still some uncertainty with how the pattern will play out. in the meantime, be sure to follow the forecast at weather.gov for any updates!
AVIATION
VFR conditions prevail at TAF sites across the forecast period. Gusty north to northwest winds through the eastern Valley, with gusts to 15-25 kts through 06Z Monday. A second period of gusty north winds develops after 12Z Monday and will continue through 18Z Monday. Sacramento TAF sites may see isolated gusts to 15 kts after 16Z Monday, but otherwise winds will be 12 kts or less.
Over the mountains and foothills, downsloping gusts 15 to 20 kts are expected through 06Z and then again after 12Z Monday.
STO WATCHES / WARNINGS / ADVISORIES
Red Flag Warning until 5 PM PDT Monday for Butte County Below 1000 ft-Central Colusa County Incl. I-5-Central Glenn Co & Interstate 5-Eastern Colusa County-Eastern Glenn County- Glenn/Colusa Coast Range Above 3000 ft-N. Sac Valley in Tehama County-Shasta Metro-Sierra (Tehama-Plumas) 1000-3000 ft- Sutter/Yuba counties below 1000 ft-W. Glenn/Colusa Foothills 1000-3000 ft.