Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
255 FXUS66 KHNX 211010 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 310 AM PDT Mon Sep 21 2026 .UPDATE...Updated Aviation section. && .KEY MESSAGES... 1. Minor Heat Risk through Tuesday as temperatures remain at or below seasonal normal values. 2. A disturbance will cross the region on Monday and Tuesday with a slight chance of showers and thunderstorms across the Sierra Nevada Monday afternoon. 3. A warming trend in temperatures starts on Wednesday as the region will see the return of heat during the latter part of the period. Thursday looks to be the hottest day with a greater than 70% chance of a Moderate Heat Risk. Friday also keeps a 40 to 60% chance of a Moderate Heat Risk. && .DISCUSSION... The cut-off low pressure system that produced today`s cloud cover will continue to move through Central California tomorrow, leading to a cooldown of several degrees and the possibility of showers and thunderstorms in the Sierra Nevada tomorrow afternoon. There is currently a 10-20% chance for thunderstorm development, with the highest chances around Mt. Whitney and slightly lower probabilities from Yosemite NP down to southern Tulare County. There is also a 40 to 60% chance for a quarter inch of rainfall in the mountainous region Fresno County and northern Tulare County, meaning these showers and thunderstorms are likely to produce more rainfall than seen in the previous summer months. After this cut-off leaves the region, ridging is expected to build back in, leading to an increase in temperatures again starting Wednesday and peaking on Thursday. The Heat Risk will start out at the Minor level on Wednesday before likely becoming a Moderate Heat Risk (60-80% chance) on Thursday where there is also a 40-50% chance for triple digits in the western half of the Valley. This heat will be short lived as the ridging pattern will quickly be replaced by a trough moving through the Pacific Northwest, causing reduced 500mb heights and cooling the region down into the low to mid 90`s. This troughing pattern is expected to continue into early next week, bringing our temperatures down to around normal for this time of year (mid to upper 80`s for the Valley, upper 80`s into the 90`s in the Mojave Desert). Looking to the long term forecast, a warming trend may pick up again by mid next week as a weak ridge builds into the region by that time. The Climate Prediction Center has our area under the leaning above normal category for temperatures in both the 6 to 10 and 8 to 14 day outlooks. So that pattern is a possibility, though other outcomes have the ridge weaker, leading to a smaller rise in temperatures. Confidence will increase as those days get closer. && .AVIATION... MVFR visibility due to smoke in the vicinity of the Dome Fire in Yosemite NP through at least this evening. There is a 10-20% chance of thunderstorms along the Sierra Nevada crest from 18Z Monday through 03Z Tuesday. Otherwise, VFR conditions prevailing for the next 24 hours. && .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. && $$ EW weather.gov/hanford