Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
420 FXUS66 KHNX 181127 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 427 AM PDT Tue Aug 18 2026 .UPDATE... Updated aviation section. && KEY MESSAGES... 1. Temperatures will gradually warm this week and rise back to around 5 degrees above average by the middle of the week. The temperatures will back down Friday into the weekend. 2. Breezy conditions take place over typical wind-prone areas including San Luis Reservoir, Lake Isabella and the Mojave Desert Slopes through this week. DISCUSSION... Continued southwesterly flow is pushing over central California this evening as the region is caught between two differing air mass systems. A cut-off low pressure trough still remains firmly in place over the eastern Pacific along with a high pressure ridge located over the southern United States. The latter of these air masses is expected to gradually shift westward through the week, building over the Desert Southwest, with influences extending into southern and central California. As the high builds in, temperatures are expected to be on the uptrend, approaching triple-digits in the Central Valley on Wednesday then passing this threshold on Thursday. Probabilities for 100 degrees in the lower elevations is around 50 to 60 percent for most communities on Wednesday, which increasing to 70 to 80 percent on Thursday. A slight cooling trend will set up into the weekend, coming about thanks to the aforementioned cutoff low tracking into the Pacific Northwest region. The low pressure appears to win out over the high, pushing the latter back eastward into the southern Great Plains. For Friday, there is a 30 to 40 percent probability for temperatures to exceed 100 degrees in the valley areas, then decreases to 20 to 30 percent for the weekend. The trend will only drop temepratures a handful of degrees, though highs are expected to return near season averages. With the warming trend through the beginning of this week, widespread areas of Moderate Heat Risk are expected, especially for the San Joaquin Valley, Sierra Nevada Foothills, and Mojave Desert. This level of heat is tolerated by the well-acclimated, but brings risk of heat-related illnesses to those sensitive to heat, such as older adults (65+), infants, athletes, outdoor workers, those without effective cooling, and those with chronic diseases. The warmer conditions will also result in lower relative humidity values across the region, especially for the areas listed above where the temperatures will be at their warmest. Valley and Sierra minimums are expected between 15 and 25 percent at their lowest point midweek, with desert values expected between 10 and 15 percent. However, overnight recoveries will be moderate to good, largely at 50 to 60 percent across the local area outside of the desert. Due to high pressure winning out in the early part of this week, winds will mostly return to being light and diurnal except for the most wind-prone locations. These include San Luis Reservoir, Lake Isabella, and the Mojave Desert Slopes in the lee of the Tehachapi Range. AVIATION... VFR conditions will prevail 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. && $$ public...McCoy aviation....BB weather.gov/hanford