Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
185 FXUS66 KSTO 172114 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 214 PM PDT Sun Aug 17 2025 .DISCUSSION... .SYNOPSIS... Below normal temperatures continue early this week with mainly Minor HeatRisk and periodically breezy onshore flow. Temperatures trend warmer mid to late week, with areas of Moderate HeatRisk developing by Thursday, with triple digit highs in the Valley. && .KEY MESSAGES... *Today - Tuesday: - Cool with below average temperature with Minor HeatRisk - Afternoon highs the mid 80s to low 90 for much of the Valley and foothills - Periodically breezy onshore flow is forecast at times, strongest in the Delta vicinity and over the Sierra Crest with good overnight humidity recovery - 10-15% chance of isolated thunderstorms in northern Shasta County early this evening, otherwise dry *Wednesday - Weekend: - Temperatures rise to near normal Wednesday, with generally Minor HeatRisk. Highs gradually trend well above normal Thursday into the weekend as high pressure builds back in over the Western US, centered over the Four Corners region. - Widespread Moderate HeatRisk returns to the forecast by Thursday as a result of the warming trend, with triple digit highs in the Valley - The hottest day is expected to be Friday, with some areas of Major HeatRisk developing and little relief overnight - Drying trend will bring lower relative humidity to the area mid to late week, around 15-20% in the afternoons - Monsoonal moisture will bring a slight chance of afternoon/evening thunderstorms to the Sierra crest south of I-80 Friday into the weekend .Changes from previous forecast... - Thunderstorm chances this evening have diminished, with just a slight chance of isolated storms for far northern Shasta County in the early evening - There is the the potential for monsoonal moisture to bring showers and thunderstorms south of I-80 Friday into the weekend && .AVIATION... Generally VFR conditions expected at interior NorCal TAF sites next 24 hours, although some 30% probabilities of MVFR/IFR conditions 12z-16z Monday in low stratus for Delta and adjacent Valley locations. Breezy onshore winds expected, with south- southwest gusts 15 to 25 kts throughout the Delta and Valley, gradually tapering after 06z Monday. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$