Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
672 FXUS66 KHNX 140602 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 1102 PM PDT Wed Aug 13 2025 .UPDATE... Aviation discussion updated to 06Z. && .KEY MESSAGES... 1. As temperatures across the region cool, the Major Heat Risk in the Mojave Desert will reduce to Moderate today and tomorrow, before becoming a Minor Risk by this Friday. 2. There is a slight (10-15%) chance for isolated thunderstorms along the Sierra Nevada crest this afternoon, with the dry conditions near the ground leading to little rainfall and the possibility for dry lightning to occur. 3. Minor fire risk with widespread minimum relative humidity between 15 and 25 percent for the non-desert areas. Minimum relative humidity expected to be less than 10 percent in the Mojave Desert with breezy winds in the afternoon to evening. && .DISCUSSION... The ridge that had been above California for the last few days has now begun to weaken in earnest as the trough from Canada makes its way south. This will lead to slightly reduced temperatures across the region, with the Mojave Desert coming out of Major Heat Risk and into a Moderate Risk today and into tomorrow. The Valley can expect mostly a Minor Heat Risk with some pockets of Moderate mainly around the coastal mountains and southern Valley. As the trough moves further south, Heat Risk for much of the region will become Minor as the Valley will see highs in the mid 90`s with probabilities for triple digits less than 10%. This trend is expected to continue through the weekend and into early next week, though a ridge may retrograde west and cause increasing temperatures once again. This movement may be influenced by an incoming tropical system in the Atlantic pushing the ridge west. Along with the cooling temperatures caused by the weaking ridge and incoming trough, a small amount of mid-level moisture may lead to the formation of isolated thunderstorms this afternoon, with the chances of cell development at 10 to 15% along the Sierra Nevada crest as well as to the lee of the mountain range. Due to the low relative humidity over the Sierras this afternoon, any rain that might fall may then evaporate before it reaches the ground, which creates the possibility for dry lightning to strike in any cell that forms. And due to the dry fuels and low moisture levels, new fire starts are a concern with any thunderstorm that develops. There is also a continued minor fire risk for the Valley as low RH`s of 15 to 25 percent remain consistent in the Valley today. The deserts will also continue to see low RH`s in the single digits as well as elevated winds along the slopes. RH`s for the Valley are likely to improve this Friday and over the weekend as temperatures cool, though winds are expected to become slightly breezier as the trough passes through California. Then with the possible ridge intrusion next week, RH`s are likely to return to similar values as we will see this afternoon. && .AVIATION... 06Z Update: VFR conditions are expected in the San Joaquin Valley for the next 24 hours. There is a 5 to 15 percent chance for mountain obscuring thunderstorms developing across the Sierra Nevada crest between 20Z Thursday and 03Z Friday. && .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. && $$ Public/Aviation/Fire Weather....EW/Molina DSS/PIO.........................McCoy weather.gov/hanford