Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
228 FXUS66 KHNX 311925 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 1225 PM PDT Sun Aug 31 2025 .KEY MESSAGES... 1. Warm than normal temperatures as chances for triple-digits sit at around 80-100 percent on Monday. Slight cooling trend as moisture enters the region. Better cooling by late in the week. 2. A slight chance (10-20 percent) for thunderstorms over the Sierra Nevada on Tuesday. Greater thunderstorm chances around Mid-week. 3. Marginal (at least 5 percent) risk of flooding in the very high elevations of the Sierra Nevada due to the increasing potential for thunderstorms Tuesday through Thursday. && .DISCUSSION... High pressure ridge is the dominate feature across the west as Central California heats-up early this week. Based on current trends, the San Joaquin Valley is expected to see considerable highs temperatures at or above 100 degrees. With the ridge pattern still building, Mondays temperatures will run higher as Heat-Risk reaches into the Major Category. Issued a Heat Advisory for the Monday time-frame when the heating peaks. Disturbances off the Pacific Coast will interact with the ridge pattern as an increase in the southerly flow draws up monsoonal moisture toward the district. A change in the weather pattern will occur early this week as abundant moisture enters the area providing a potential for significant precipitation. Ensemble moisture analysis is showing a surge of the monsoonal moisture expected to reach Central California by Tuesday. Once the ridge is shifted by the off-shore disturbances interacting with the ridge, a stronger southerly flow will allow for a northward surge of moisture that will see additional sources of moisture introduced from the tropics. Ensemble upper-air analysis is still showing a weak disturbance aiming for the Monterey/Bay-Area with enough energy to fire-up convection across the Interior Central California area. Therefore, by Tuesday, Probability of Measurable Precipitation (PoP) along with instability analysis shows increasing percentages as significant moisture has the potential of entering the region. With PoP values reaching 40 to 60 percent, a good chance exist of generating significant accumulations. Thunderstorms may even have the capacity of introducing heavy rain as guidance shows percentages reaching at least 5 percent of meeting excessive precipitation criteria from Tuesday through Thursday across the Sierra Nevada and the Mountains and Desert of Kern County. The ridge pattern is shifted east starting on Friday as the probabilities of cooling and drying increase across Central California. Friday will be a period of transition as drying and cooling will start with lingering moisture and heat still in place. Next weekend is showing higher probabilities of significant cooling and drying as a disturbance digs through Northern California. By that point, convection will be limited to the back-country of Yosemite. && .AVIATION... 18Z Update: VFR conditions will prevail across the central California interior for the next 24 hours. Less than 10% chance of Sierra Crest thunderstorms during the period. && .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... Heat Advisory from noon Monday to midnight PDT Monday night for CAZ300>304-306>314-316-317-319-321. && $$ public...Molina aviation....BSO weather.gov/hanford