Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
891 FXUS66 KHNX 290906 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 206 AM PDT Mon Sep 29 2025 && .KEY MESSAGES... 1. Thunderstorms are once again possible this afternoon in the Sierra Nevada, with a 15-35% chance for development. These probabilities will be mainly north of Tulare County, and the highest chances in Mariposa County and Yosemite National Park. 2. A small area of Marginal Risk (at lest 5%) of excessive rainfall remains today in the mountainous region of Mariposa County and into Madera County. 3. The next week is expected to be dominated by below normal temperatures, with the Valley likely seeing highs in the mid to lower 80`s through this weekend. && .DISCUSSION... As of current models, today is the last day with strong chances for mountain thunderstorms, with a probability of 15 to 35% for development this afternoon. This is due to an incoming trough from the Pacific, which will bring in enough energy along the Sierra Nevada to uplift the remaining moisture into becoming thunderstorm cells. These cells are most likely to form along the Sierra Nevada crest north of Kern County from 11am through 8pm. The area with the greatest chance for development this afternoon is expected in the mountainous portion of Mariposa County and around Yosemite National Park. This area also has a Marginal Risk (at least 5%) of excessive rainfall due to this possibility. Tomorrow afternoon sees these chances fall off a cliff below 10%, with similar chances on Wednesday, which is due to the passage of the main front of the trough and the cooler air behind it will limit uplifting of moisture. Another trough may come close to our CWA by Thursday, but it is likely to only clip Yosemite, which will keep thunderstorm chances low. Model ensembles begin to deviate more by Friday. One ensemble shows a trough directly over our CWA, which would lead to stronger chances for thunderstorms, but another ensemble has that trough further north, which would not affect our CWA nearly as much in the aspect. In either case, however, the effect on temperatures will be a consistent pattern of below normal temperatures throughout the week, though the actual numbers may fluctuate by a few degrees over time. This will be caused by consistent troughing through the week. && .AVIATION... 12Z Update: A 15-35 percent chance of thunderstorms from 18Z Monday through 03Z Tuesday will exist across the Sierra Nevada. Ceilings lower to around 10k feet in spots around 18Z Monday. Otherwise, VFR conditions expected 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... None. && $$ EW weather.gov/hanford