062 FXUS66 KSTO 091943 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 1243 PM PDT Mon Jun 9 2025 For additional details on weather and expected impacts over the next 7 days, please visit weather.gov/sto/briefing. .DISCUSSION... .SYNOPSIS... Isolated shower/thunderstorm chances over higher terrain persist today and Tuesday primarily north of Interstate 80 as the split flow regime aloft begins to deteriorate. Broad zonal flow is then expected to set up across interior NorCal through the remainder of the week, with troughing arriving into next weekend. As a result, an overall stagnating weather pattern of predominantly dry weather, near normal temperatures, and breezy onshore flow looks to persist. && .KEY MESSAGES... * Heat Advisory in effect through 11 PM PDT tonight for portions of the northern Sacramento Valley and adjacent mountains/foothills. * Today-Tuesday: -Widespread Moderate HeatRisk across interior NorCal and areas of Major HeatRisk across the northern Sacramento Valley today, dissipating to areas of Moderate HeatRisk by Tuesday. --Probability of Valley High Temperatures > 95F: ---Northern/Central Sacramento Valley: 80-100% Today, 60-90% Tuesday ---Delta, S. Sacramento Valley, N. San Joaquin Valley: 20-50% Today & Tuesday --Probability of Valley High Temperatures > 100F: ---Northern/Central Sacramento Valley: 60-90%, Today -Periodically breezy onshore flow, strongest in the Delta and vicinity during the afternoons and evenings. -Chances for isolated afternoon/early evening showers and thunderstorms: --Today: 15-30%, across Sierra/southern Cascades north of Interstate 80 and northern Sacramento Valley and surrounding terrain. --Tuesday: 5-15%, across Shasta County mountains * Wednesday-Sunday: -Gradual cooling trend expected through the remainder of the week. Primarily Minor HeatRisk as temperatures become more seasonable. -Probability of Valley High Temperatures > 90F: --Northern/Central Sacramento Valley: 60-90% Wed-Thu, 30-50% Fri-Sun --Delta, S. Sacramento Valley, N. San Joaquin Valley: 50-80% Wed-Thu, 20-40% Fri-Sun -Onshore flow expected to persist with periods of breezy winds, mainly in the afternoons and evenings and strongest across the Delta and vicinity. -Ensemble uncertainty in a trough digging southward from the Gulf of Alaska next weekend persists. Current trends indicate a continuation of seasonable and breezy weather anticipated at this time. .Changes from previous forecast... -No notable forecast changes since last update. && .AVIATION... VFR conditions expected at Valley TAF sites next 24 hours, with possible MVFR/IFR conditions in isolated mountain and foothill t-storms from around 20z today through 05z Tuesday. Mostly onshore flow in the Valley/Delta, with surface winds at or below 15 knots. Period of gustier surface winds from around 21z through 16z Tuesday, with surface gusts up to 25 knots possible. && .STO WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 11 PM PDT this evening for Northern Sacramento Valley-Shasta Lake Area / Northern Shasta County. && $$