872 FXUS66 KSTO 242048 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 148 PM PDT Thu Jul 24 2025 .DISCUSSION... .SYNOPSIS... Below-normal temperatures and breezy onshore winds. Chances for afternoon and evening mountain thunderstorms today through the weekend, with chances for isolated showers over the Valley and Sierra foothills through Friday. && .KEY MESSAGES... * Today-Friday: - Afternoon highs in the 80s and low 90s throughout the Valley as below normal highs continue this week. - Onshore winds will be breezy to gusty through the Delta and into the Valley. Thunderstorms: - Chances (15-30%) for isolated to scattered mountain showers and thunderstorms during the afternoon and evening hours. - As an offshore low pressure system moves inland today, storms that develop over the mountains will generally move to the northwest, with the majority of thunderstorm activity occurring outside of interior Northern California today. - There is increasing confidence that a few stray showers will develop over the Sierra foothills and portions of the Sacramento Valley during the overnight hours tonight into Friday morning. - On Friday, as the low moves further south, storm motion over the mountains will be largely southeasterly over the Coastal Range, allowing for a 15-20% chance of isolated thunderstorms in the northern Sacramento Valley. Storm motion over the Sierra will be largely northeast/westerly, but individual storms will be subject to terrain influences. - The majority of thunderstorms will be wet, with the potential for isolated dry lightning. - Elevated fire weather conditions are expected in the mountains through Friday and into the weekend due to the lightning threat. - Any strikes outside the main precipitation core will pose the threat for fire starts. * Saturday-Sunday: - Chances (15-20%) for isolated to scattered mountain showers and thunderstorms continue on Saturday and Sunday remaining largely confined to the Sierra, with the highest potential on Saturday. - Storms are expected to form along the Sierra crest and move northeastward on Saturday, resulting in most of the activity occurring outside of interior Northern California. - Thunderstorm chances decrease on Sunday over the Sierra to 10-15%. - Temperatures are expected to remain below-normal through the weekend with a slight warming and drying trend beginning on Sunday. - Onshore winds will be breezy to gusty through the Delta and Valley, especially during the late afternoon and evening hours. * Long Term: - Cluster Analysis supports heights flattening out as riding over the Pacific Northwest encroaches into Northern California early next week. - Temperatures will follow a warming trend Monday through Wednesday, with weaker but still breezy onshore winds compared to the weekend. .Changes from previous forecast... - Increased potential for isolated foothills/Valley showers overnight Thursday into Friday. - 10-20% chance of isolated showers and thunderstorms in the northern Sacramento Valley on Friday. && .AVIATION... Mostly VFR conditions expected over the next 24 hours across Interior NorCal. Isolated thunderstorms may cause MVFR/IFR conditions along the Sierra Crest this afternoon and evening. There is a slight chance for the storms to move over the Valley as showers this evening and overnight, bringing potential for brief periods of MVFR to portions of the Valley as well. For the Valley, south to southwest surface winds generally less than 12 kts with gusts up to 15 to 20 kts through 03z Friday and again after 22Z Friday. For the Delta vicinity, sustained winds 10 to 20 kts with gusts 20 to 30 kts at times. Non-zero chance (less than 10%) for a few low clouds around 1000-2000 ft from 12Z to 16Z Friday in the Delta and adjacent Valley locations. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$