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The Latest NWS Regional Area Forecast Discussions
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NWS Area Weather Forecast Discussion
County Warning Area [CWA]: STO Regional NWS Weather Office: Sacramento, CA 584 FXUS66 KSTO 152139 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 139 PM PST Mon Dec 15 2025 For additional details on weather and expected impacts over the next 7 days, please visit weather.gov/sto/briefing. .KEY MESSAGES... - Fog, mist, and low clouds for the Central Valley, Delta, and adjacent foothills continues tonight into early Tuesday. - High temperatures in the Central Valley, Delta, and lower foothills will gradually trend to more mild levels by the middle of the week. - Series of disturbances will bring periods of beneficial rain, breezy south winds and isolated thunderstorms at times from Tuesday into the weekend. - Active weather pattern continues into next weekend, including the holiday travel period, though details remain uncertain. && .DISCUSSION... ...Today - Tonight... Latest satellite imagery continues to show the low stratus deck and patchy fog across the Central Valley and adjacent foothills. A few areas in the northern Sacramento Valley have clear out and temperatures to warm, while the low clouds linger elsewhere. Temperatures underneath the stratus have been well below normal for highs, and areas above the stratus continue to be above average. A disturbance over the Pacific Northwest brushes through far Northern California tonight, bringing some scattered showers to the northern Coastal Range and Shasta County. Dense fog may continue overnight into Tuesday morning, with visibility reductions to a quarter mile or less for areas within the Central Valley. ...Tuesday - Thursday... An upper level wave moves in Tuesday increasing precipitation chances and breezy conditions to the region. Look for continued low ceilings, mist, and foggy conditions Tuesday morning. Precipitation spreads southward through Tuesday, but remains along and north of the I-80 area for the day, then over much of the rest of the area Tuesday night. Coverage will be isolated for the showers for much of Tuesday. By the afternoon instability and moisture increase across the forecast area giving way to thunderstorm chances, though these have trended lower, now 10-15 percent across the area. Best chances will be within the Sierra, Motherlode, Sacramento Valley, and Coastal Range. Coverage will be scattered to widespread across the area for precipitation. With snow levels above 8000 feet, no impacts are expected. A brief lull in precipitation is expected Thursday morning and afternoon, before another round of precipitation moves into the region bringing breezier conditions. ...Friday Onward... An active pattern continues for Friday and into the weekend, with another upper level wave moving out of the eastern Pacific. This system has trended cooler over the past couple of runs of the NBM. Snow levels have trended a little higher and are looking to be above 7500 feet by Friday afternoon and evening and remaining so through the weekend, which has reduced forecast snowfall amounts and should limit travel impacts. Moisture content has trended higher with the system, with chances for widespread largely beneficial precipitation. Breezy conditions are expected with the system as it moves through the area. Confidence remains low on the full development, track, and snow levels with the system, especially into next week. Stay tuned for details! && .AVIATION... Low ceilings and visibilities continue for areas within the Central Valley. Clearing has been observed near RDD and RBL this afternoon, which will be short lived. By this evening stratus will move back into the northern Sacramento Valley, with increasing chances for precipitation. Areas around Sacramento and the San Joaquin Valley will continue to see low stratus and foggy conditions throughout today. Some improvements to the ceilings and visibilities this afternoon before conditions deteriorate again later this evening and overnight. Light and variable winds are expected through the TAF period. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$
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