Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
341 FXUS66 KHNX 172001 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 101 PM PDT Wed Jul 17 2024 && .KEY MESSAGES... 1. Excessive Heat Watch in effect for the Kern County Desert and Desert slopes beginning 11 AM Sunday and in effect for the San Joaquin Valley, Yosemite Valley, Lake Isabella, and Sierra Nevada foothills beginning 11 AM Monday. 2. The high risk of grass fires in the valley continues, with fire behavior enhanced even with low wind speeds. In the Sierra Nevada, the risk increases with afternoon thunderstorms possible from Thursday through Sunday. 3. Periods of afternoon thunderstorms in the Sierra Nevada continue this week. The greatest chances will be Thursday and Friday with a 15 to 25 percent probability. Saturday and Sunday have a 10 to 20 percent probability of thunderstorms in the Sierra Nevada. 4. There is a 35 to 70 percent probability of a high of at least 110 in the San Joaquin Valley on Monday. The probability goes up to 55 to 80 percent for Tuesday in the Valley. && .DISCUSSION... We currently have a ridge sitting over the Four Corners region of the United States with a mostly onshore flow for most of California bringing temperatures down a bit. However, latest model ensembles are in strong agreement that this ridge will slide back to the west and amplify over the next few days. This amplification and movement of the ridge will bring hotter temperatures back into the picture for Central California. The shift in the positioning of the ridge will also change the flow in the higher levels leading to some monsoonal moisture to move in over the Sierra Nevada for the next few days. This increase in moisture brings an increase in potential for thunderstorms. These thunderstorms can produce dry lightning leading to more fires. Latest probabilities have a 15 to 25 percent chance of thunderstorms Thursday and Friday before decreasing to 10 to 20 percent on Saturday and Sunday. The main concern with the ridge is the hot temperatures that will be brought along. The temperatures will gradually increase as we head into the weekend into next week. Latest probabilities have a 40 to 75 percent chance of a high temperature of at least 105 degrees between Friday and Sunday. However, a bigger concern is the probabilities of highs of at least 110 which will be in 40 to 80 percent range for most of the Valley from Monday to Wednesday. Tuesday has the highest probabilities of highs of at least 110 with Merced having 55 percent, Fresno, Hanford and Visalia at 80 percent, and Bakersfield at 70 percent. These percentages have led to the issuance of an Excessive Heat Watch beginning Monday. The risk is higher in the Mojave Desert Slopes where an Excessive Heat Watch begins on Sunday. && .AVIATION... Areas of MVFR and local IFR visibility will continue in and around wildfires. Otherwise, VFR conditions will prevail across the central CA interior over 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... Excessive Heat Watch from Sunday morning through Wednesday morning for CAZ337>339. Excessive Heat Watch from Monday morning through Wednesday morning for CAZ300>321-324-325-332. && $$ JPK weather.gov/hanford