FXUS66 KHNX 191039 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 339 AM PDT Fri Jul 19 2024 && .KEY MESSAGES... 1. An Excessive Heat Warning is in effect for the Kern County Desert and Mojave Desert SLopes beginning 11 AM PDT Sunday and in effect for the San Joaquin Valley, Yosemite Valley, Lake Isabella, and Sierra Nevada foothills beginning 11 AM PDT Monday. Both warnings are in effect through 11 PM PDT Wednesday. 2. The high risk of grass fires in the valley continues, with enhanced fire behavior even with lower wind speeds. IN the Sierra Nevada, the risk increases with afternoon thunderstorms possible from Thursday through Sunday. 3. Periods of afternoon thunderstorms in the Sierra Nevada continue through the weekend and into next week. There is a 10 to 20 percent probability each afternoon. 4. There is a 40 to 70 percent chance for afternoon highs to reach or exceed 105 degrees in the San Joaquin Valley on Monday, chances increase to 75 to 95 percent for Tuesday and Wednesday. && .DISCUSSION... The warm up has started again over central California, with temperatures across the region returning into the triple digits Thursday afternoon. This comes as the result from an upper level ridge sliding over the western United States, which will dominate the synoptic pattern through the next week. Probabilistic guidance from the National Blend of Models suggests a 20 to 30 percent chance for temperatures to reach or exceed 105 degrees this afternoon and Saturday for the San Joaquin Valley outside of Bakersfield, which has a 30 to 60 percent chance. A slightly cooler day on Sunday, the NBM shows less than a 20 percent chance for 105 degree highs, but at least a 50 percent chance for triple-digit heat from Fresno southward. The brunt of the heat is anticipated to arrive early next week, with a moderate to high (60 to 90 percent) probability to return to temperatures at or above 105 degrees on Tuesday. There is also a 20 to 30 percent chance for afternoon highs to exceed 110 degrees. Poor overnight recoveries will also result from the high pressure system aloft, with at least a 70 percent chance of lows greater than 75 degrees Wednesday and Thursday mornings. This will contribute to Major to Extreme Heat Risk impacts, mainly across the San Joaquin Valley and Kern County Desert. An Excessive Heat Warning is in effect for these areas through Wednesday night, starting on Sunday for the desert region, and the valley on Monday due to the gradual westward expansion of the aforementioned high. In addition to the hotter temperatures, the anticyclonic flow around the ridge will shift upper level winds to the south, bringing increased moisture to central California from the eastern Pacific. The combination of warmer temperatures, increased relative humidity, and terrain-driven convergence will result in potential convection along the crests of the Sierra Nevada each afternoon. Dangerous cloud to ground lightning, small hail, gusty and erratic winds, and elevated rainfall rates are the main threats with any showers and thunderstorms that may develop over the area. Lightning strikes on dry grasses could also lead to the ignition and spread of fires. Ensemble guidance suggests a 10 to 20 percent probability for thunderstorms each day through midweek. However, chances are progged to increase slightly to 15 to 25 percent during the late week as a trough sets up off the California coast, extending southward from a low pressure system that is forecast to track through the Pacific Northwest region. && .AVIATION... Areas of MVFR and local mountain obscuring IFR in showers and thunderstorms over higher elevations of the Sierra Nevada through 00Z Saturday. Areas of MVFR and local IFR visibility will continue in and around wildfires. Otherwise, VFR conditions will prevail across the central CA interior over the next 24 hours. && .AIR QUALITY ISSUES... ISSUED: 07/18/2024 14:32 EXPIRES: 07/19/2024 23:59 None. && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback. && .HNX WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning from 11 AM Sunday to 11 PM PDT Wednesday for CAZ337>339. Excessive Heat Warning from 11 AM Monday to 11 PM PDT Wednesday for CAZ300>321-324-325-332. && $$ public/aviation...SM IDSS.............VJP weather.gov/hanford