Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
263 FXUS66 KHNX 291005 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 305 AM PDT Sat Jun 29 2024 && .KEY MESSAGES... 1. Warming continues this weekend, before a dangerous, long- duration heat wave hits the central valley of California through the holiday week and into next weekend. 2. An Excessive Heat Warning has been issued for Tuesday July 2nd through Saturday July 6th, and may need to be extended through next weekend as the event nears. 3. The risk of grass fires will continue to increase with herbaceous fuel loading at or near 120% of normal. A long period of excessive heat, minimum relative humidities near 15% and poor overnight relative humidity recoveries may require a Fire Weather Watch as the event nears. 4. During the middle and late next week, a 15%-20% chance of thunderstorms will reside across the Sierra from Fresno County to Yosemite National Park. && .DISCUSSION... The most probable scenarios when analyzing the ensembles of the North American model suite, show a strong high pressure parked over California or the Four Corners region during the heat wave. There are a few less probable scenarios that indicate a weaker area of high pressure or one that is displaced further northwest or southwest. However, confidence is high enough to upgrade the Excessive Heat Watch to a Warning. NBM High and Min temperature probabilities are impressive, and this meteorologist has not seen a 30% probability of maximum temperatures exceeding 110F during the hottest days, which look to be July 3rd through July 5th, since NBM Probability of Exceedance values have become available. Probabilities of very warm overnight temperatures are also unusual, which is the reason why the HeatRisk will High to Extreme. Preparation for this extreme heat event should begin as soon as possible, based upon how vulnerable our communities are to this type of event occuring over the 4th of July. In the longer term, moisture increases slightly in the middle levels of the atmosphere, leading to a 15%-25% of thunderstorms or dry lightning in the foothills and high Sierra late next week, from Thursday through next weekend. && .AVIATION... Continued areas of MVFR and local IFR visibility due to smoke nearby the Fresno County fires will continue in the Sierra Nevada and adjacent foothills. Otherwise, VFR conditions will prevail across the central California interior for the next 24 hours. && .FIRE WEATHER... The multiple grass fire over the past several weeks have been unusually numerous and quick to spread, even in the absence of wind. Winds will continue to be terrain driven, with typical stronger gusts around sunset as has been the case this week. Per the Fuels and Fire Behavior Advisory issued by the USFS Predictive Services, typically low to moderate wind speeds can have a greater affect on rates of spread than normal. In addition, with the incoming heat wave, the Energy Release Component is forecast to near the climatological max on and after July 1st, and so are the 100 and 1000 hr fuel moistures for the Central Valley. So the risk of grass fires will be near their peak around the 4th of July. && .AIR QUALITY ISSUES... Air Quality Alert due to smoke impacts from wildfires. && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is high. 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 Warning from 11 AM Tuesday to 8 PM PDT Saturday for CAZ300>322-324-332-334-336>339. && $$ public...KM/SM aviation....KM weather.gov/hanford