Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
633 FXUS66 KHNX 160017 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 517 PM PDT Mon Sep 15 2025 .UPDATE... Updated Aviation Section. && .KEY MESSAGES... 1. A warming tend will continue into the middle of the week, with the warmest temperatures Tuesday. Minor chances (less than 30 percent) to exceed 100 degrees Tuesday and Wednesday for localized areas of the San Joaquin Valley and Mojave Desert. 2. Smoke will continue to linger as the Garnet Fire continues to burn but with improving conditions; smoke will not be as thick or widespread as in previous weeks. 3. Chance for showers an thunderstorms late this week as tropical moisture tracks over the region from the south. Thursday will bring the greatest chances for storms at 15 to 25 percent, however there is a chance for storms as early as Wednesday afternoon that may result in dry lightning. 4. There is a Marginal Risk (5 to 15 percent) for Excessive Rainfall leading to flash flooding on Thursday for Kern County and the southern Sierra Nevada. There is also a Marginal Risk on Friday in the Sierra Nevada extending from Yosemite National Park to Sequoia National Park. && .DISCUSSION... High pressure building over central California through Wednesday will bring about clear conditions with warming temperatures that will result in afternoon highs up to seven degrees above average for this time of year. Stagnant air aloft associated with the high pressure will keep smoke from the Garnet Fire from being easily dispersed, causing hazy skies to continue for the next couple of days though not as concentrated as in previous weeks. A change in conditions is expected in the latter part of this week as moisture approaches the region from the south. Tropical storm Mario, presently located in the east Pacific off the coast of Baja California is projected to phase with a secondary low pressure system currently centered off the southern California coast. Cyclonic flow around the secondary low will cause the moisture from the post-tropical system to track northward into southern and central California as early as Wednesday afternoon, however timing of the influx of moisture has been trending later in recent model runs towards Wednesday night into Thursday. The nighttime approach of moisture may limit convective development but still bring chances for showers starting through Kern County and extending north through Thursday. && .AVIATION... 00Z Update: VFR conditions will prevail across the Central California Interior for the next 24 hours. Areas of Dense Smoke aloft along the Sierra Nevada over eastern Fresno County and nearby counties from the Garnet Fire may impact visibility. && .FIRE WEATHER... Rising temperatures this week will cause a drop in relative humidities, with widespread minimums 20 to 25 percent through Wednesday across the San Joaquin Valley and Sierra Nevada; min RHs 10 to 15 percent are projected for the Mojave Desert. The approaching moisture tracking over the warmer temperatures and lower RHs will bring about some risk for dry lightning Wednesday afternoon should thunderstorms develop during the period. However, as stated, the main influx of moisture is projected to move into the region Wednesday night into Thursday which will improve RHs. Mixing heights for the valley areas will hold mostly steady at 7000 to 8000 feet ahead of the moisture, however mixing heights in the Mojave Desert and Kern County mountains are expected to exceed 10000 feet, which could lead to plume dominated fire if any develop. && .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... None. && $$ public/aviation...McCoy/EW idss..............Molina weather.gov/hanford