Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
826 FXUS66 KHNX 210539 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 1039 PM PDT Wed Aug 20 2025 .UPDATE... Aviation Section Updated && && .KEY MESSAGES... 1. A significant warming trend returns for the remainder of the week with triple digit heat in the warmest locations. The potential for Major Heat Risk returns by Thursday in the Kern County desert and enters into the Central Valley by Friday. 2. An Extreme Heat Warning has been issued for the Kern Desert valid starting tomorrow and extending through Sunday. A Warning has also been issued for the Sierra foothills and the urban areas of the San Joaquin Valley beginning Friday. A Heat Advisory has been issued for the remaining areas of the San Joaquin Valley and the Lake Isabella area. 3. A Red Flag Warning has been issued for the Frazier Park and Grapevine areas in southern Kern County valid this morning through Saturday evening due to low relative humidity and locally breezy winds. Elevated fire risk with minimum relative humidity expected to be less than 10 percent in the Mojave Desert and Kern County mountains with breezy winds in the afternoon to evening. 4. There is a 10 to 30 percent chance for thunderstorms this weekend with an influx of monsoonal moisture, with the greatest chances along the Sierra crest. && .DISCUSSION... An area of high pressure continues to build over the Desert Southwest today and spread across central California, drawing unseasonably warm air from the south-southwest. Triple digit highs are likely to return tomorrow for much of the San Joaquin Valley, Kern Desert, and the Lake Isabella area, with a 50 to 80 percent chance to exceed 105 degrees on Friday and a 40 to 70 percent chance on Saturday. Multiple heat products have been issued for these areas due in part to the warmer daytime conditions; however, widespread minimum temperatures in the 70s are expected along with localized minimums in the 80s, particularly in the urban areas and in the foothill areas affected by the thermal belt. The southwesterly flow around the high is also expected to cause an influx of monsoonal moisture through the mid levels of the atmosphere. The additional moisture lifting along the Sierra Nevada combining with the warmer valley air will result in isolated to scattered showers and thunderstorms in the higher elevations. There is a 30 to 50 percent chance for 24 hour totals ending 5 PM PDT Sunday to exceed 0.1" for the areas above 2500 feet, and up to a 65 percent chance for the highest elevations of Fresno and Tulare Counties. && .AVIATION... 6Z Update: VFR conditions are expected in the San Joaquin Valley for the next 24 hours. && .FIRE WEATHER... Warming temperatures across the region will cause minimum relative humidity to lower for much of the lower elevations of the area (the influx of moisture in the mid levels will cause RH to increase in the Sierra). Widespread minimums 15 to 20 percent are expected for the San Joaquin Valley and Kern County mountains and less than 15 percent in the Kern Desert. Lowering RHs paired with stronger southerly wind gusts near 25 mph in Frazier Park and Fort Tejon has led to the issuance of a Fire Weather Watch as these conditions can cause rapid fire spread if development occurs. && .AIR QUALITY ISSUES... 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... Extreme Heat Warning from 11 AM Thursday to 8 AM PDT Sunday for CAZ337>339. Extreme Heat Warning from 11 AM Friday to 8 AM PDT Sunday for CAZ300-304-307-308-313-314-316-317-319-321. Heat Advisory from 11 AM Friday to 8 AM PDT Sunday for CAZ301>303-305-306-309>312-315-332. Red Flag Warning until 9 PM PDT Saturday for CAZ597. && $$ public...SM aviation....JPK weather.gov/hanford