FXUS66 KSTO 192031 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 131 PM PDT Fri Jul 19 2024 .SYNOPSIS... Hot weather persists into next week. Thunderstorm chances along and east of the Sierra/Cascade crest into next week as well. && .Discussion... Afternoon GOES-18 Satellite imagery shows relatively clear skies across interior NorCal. Some smoke in the mid-levels from the SoCal fires and far northwestern California can be seen on satellite imagery as well. We are anticipating another day of triple-digits around NorCal, and at the time of this writing our Sacramento weather observation station is at 99F. Our hot weather is expected to continue through the weekend, thanks to an upper level ridge of high pressure located in the Great Basin. The high pressure is projected to remain in this location as we move into Saturday, while a short-wave trough is forecast to lift northward along the California coast and enhance the Delta Breeze and cool temperatures off in the Delta influenced areas. The trough will also tap into monsoonal moisture + instability that is embedded within the Great Basin ridge, so showers/thunderstorms along the Sierra Crest are possible tomorrow. The best chances of storms will be south of HWY-50, then as the shortwave lifts further northward, chances increase for locations in the northern mountains/Southern Cascades/Burney Basin in the late afternoon and evening hours. A slight cooldown around interior NorCal is expected on Sunday thanks to the short-wave trough that moved through. High temperatures will range from 90 to 107, with the coolest temperatures in the Delta and the warmest in the northern Sacramento Valley. Thunderstorm chances will once again exist for the Sierra Crest, mainly south of HWY-50, in the afternoon/evening hours as we will continue to see monsoonal moisture surges as a result of the ridge of high pressure southeast of our area. Monday, interior NorCal will once again see widespread triple digits as the high pressure will be firmly parked over our area, which will help diminish the Delta Breeze's cooling influence. Widespread Moderate HeatRisk will return on Monday, along with some isolated areas of Major HeatRisk in the northern Sacramento Valley. Isolated (10-15% chance) thunderstorms exist as well in the high Sierra, once again mainly south of HWY-50, as monsoonal moisture/instability continues to move through the mountains. && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... Upper level high continues to be located over interior NorCal as we move into the extended period. Resulting high temperatures will continue to climb and be in the triple digits across our region. The hottest day appears to be Tuesday, with temperatures ranging from 100-110, where the hottest highs will be in the northern Sacramento Valley. The high temperatures, along with poor overnight recoveries (low temperatures) will result in widespread Moderate to Major HeatRisk, with isolated areas of Extreme HeatRisk (mainly in the thermal belts of the Foothills) on Tuesday. Wednesday, we can expect more of the same, although the high pressure will weaken and slowly be replaced by upper level troughing, which will start to cool things down slightly for the region on Friday. Overall, Cluster Analysis is in relatively good agreement of the troughing pattern emerging on Friday. Monsoonal moisture advecting through the high pressure, coupled with the Sierra as the forcing mechanism, could result in isolated thunderstorm chances along the Sierra Crest Tuesday - Thursday, before troughing moves in and helps reduce the threat. && JTW .AVIATION... VFR conditions prevail across interior NorCal for the next 24 hrs. Surface winds generally below 12 knots, except in the Delta vicinity, where surface winds up to 20 knots are possible. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$