Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
722 FXUS66 KHNX 241809 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 1109 AM PDT Sun Aug 24 2025 && .KEY MESSAGES... 1. There is up to a 40 percent chance for thunderstorms this afternoon along the Sierra Crest associated with monsoonal moisture across the area. A Slight Risk (greater than 15 percent) of excessive rainfall has led to the issuance of a Flood Watch for the Sierra Nevada extending from Yosemite National Park to northern Tulare County valid through 9 PM this evening. There is a 40 to 70 percent chance for rainfall along the higher elevations to exceed one quarter of an inch through 11 PM this evening. 2. Unseasonably warm temperatures continue over the next few days with widespread triple digit heat. A slight cooling trend will set up through the week. An Extreme Heat Warning and Heat Advisory continue through Monday morning for the southern areas of the San Joaquin Valley due to warmer than average maximum and minimum temperatures. && .DISCUSSION... Monsoonal moisture and heat continues to flow into Central California thanks to the ridge of high pressure that has set up over much of the Southwest U.S. Expect above average temperatures once again today, but with increased humidity and cloud cover at times. The triple digit temperatures this afternoon and warm overnight lows tomorrow morning in the 70s to low 80s has led to the extension of the Extreme Heat Warning and Heat Advisory for the southern San Joaquin Valley through Monday morning. A gradual cooling trend will set up for the week afterwards, with daily maximums approaching season averages in the low 90s towards the end of the week. Isolated to scattered thunderstorms are anticipated to develop over the Sierra Nevada this afternoon associated with the aforementioned monsoon moisture. Warming temperatures this afternoon will allow convective activity to flourish in the Sierra, with up to a 45 percent chance for thunderstorms in areas such as Tioga Pass, Lake Thomas Edison, and Mather`s Pass. The Weather Prediction Center has given this area a Slight Risk (greater than 15%) for Excessive Rainfall leading to flash flooding. Piggy-backing off this, a Flood Watch has been issued for this area valid until 9 PM this evening as rainfall rates in developed storms may result in localized instances of flash flooding. Frequent lightning and small hail remain the additional concerns for any convective development. Albeit with the upcoming cooling trend, thunderstorm development continues to be expected through the middle portion of the upcoming week with probabilities still between 20 and 40 percent each afternoon in the Sierra Nevada. && .AVIATION... 18Z Update: A 20 to 40 percent chance of thunderstorms over the Sierra Nevada and adjacent foothills and a 5 to 15 percent chance of thunderstorms over the valley and desert for the next 24 hours. Otherwise, VFR conditions are expected in the San Joaquin Valley for the next 24 hours. && .AIR QUALITY ISSUES... None. && .CERTAINTY... The level of certainty for days 1 and 2 is medium. 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 until 8 AM PDT Monday for CAZ304-307-308- 313-314-316-319-321. Heat Advisory until 8 AM PDT Monday for CAZ305-306-309>312-315- 332. Flood Watch until 9 PM PDT this evening for CAZ323-326>328. && $$ public/aviation...McCoy idss/pio..........BSO weather.gov/hanford