Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA
Issued by NWS San Joaquin Valley, CA
000 FXUS66 KHNX 211919 AFDHNX Area Forecast Discussion National Weather Service Hanford CA 1219 PM PDT Fri Mar 21 2025 && .KEY MESSAGES... 1. Northwest winds behind the midweek system will result in low to moderate chances (20-60%) for wind gusts greater than 45 mph in the Mojave Slopes continuing today and Saturday. 2. Temperatures will remain consistently near to just below average into tomorrow. A stronger area of high pressure early next week is favorable to bring temperatures well above average to the region. 3. Warmer conditions with increasing surface moisture has a slight chance to produce afternoon thunderstorms in the foothill areas of the Sierra Nevada Monday through Wednesday. 4. There is potential for a system to pass through central California late next week, with the 6-10 day extended outlook giving a 33-40% chance for above average precipitation. && .DISCUSSION... West to northwest flow is currently present across central California as a pair of systems are moving to our north, with the leading system over the northern Great Plains and the second system cascading into the Pacific Northwest. Cyclonic flow around the systems is resulting in a moderate amount of upper level moisture passing over our region. However with little in the way of low level moisture, surface conditions remain clear for much of the area. The atmospheric flow is also resulting in warm, near-average temperatures across central California. There is a 90 to 100 percent chance for afternoon temperatures to exceed 65 degrees today in the San Joaquin Valley, with a 20 to 70 percent chance to exceed 70 degrees, with the greatest probabilities in the eastern valley areas. Averages for this time of year typically range from the upper 60s to low 70s for the central valley. Similar conditions are expected for tomorrow as the atmospheric flow remains consistent to today. Our next major pattern change still looks favorable to occur on Sunday as model ensemble guidance continues to indicate a stronger high pressure ridge will build over the southwest United States into the early week period. A significant warm up will develop for the region as a result. There is an 80 to 100 percent chance for temperatures to exceed 70 degrees on Sunday, but with a 20 to 50 percent chance for 75 degrees in the eastern San Joaquin Valley and up to a 70 percent chance for the western valley areas. Monday will likely be the first 80 degree day of the year for many locations in the San Joaquin Valley. Much of the area has an 80 to 100 percent chance to exceed 80, with Merced county being an outlier at 30 to 60 percent; though, the probabilities increase to 70 to 95 percent for Merced on Tuesday. Tuesday also has a moderate to likely chance (50 to 90 percent) to be the regions first day with afternoon highs above 85 degrees. In addition to the warmer temperatures early next week, the upper level pattern over the region is also conducive for thunderstorm development, especially along the Sierra foothills. While the aforementioned ridge tracks slightly eastward over the Great Basin, ensemble guidance continues to suggest a localized shortwave trough will develop off the southern California coast. The cyclonic flow around the trough, coupled with anticyclonic flow around the ridge, will bring increased moisture alongside the warmer temperatures to the region Tuesday. This combination has the potential to create enough atmospheric instability for thunderstorm development. The NBM has trended up in the probabilities for 500 J/kg of CAPE for Tuesday afternoon, now extending a 60 to 90 percent chance along the entire eastern reach of the San Joaquin Valley and Sierra foothills. However, warm-air-advection in the 850 mb level may produce a weak temperature inversion in the lower levels of the atmosphere, which can hinder thunderstorm development, especially in the valley areas. Meanwhile, the foothill areas are largely above the capping inversion, which would allow the air to lift freely. In addition to the conditions listed above, ensemble guidance also continues to suggest a system moving through the area late next week. However, current NBM ensemble output gives a 25 to 50 percent chance for 24 hour precipitation greater than 0.01 inches for the period ending 5 PM Thursday. These values are near normal for this time of year as we approach the end of our wet season, and so the NWS CPCs 6 to 10 day outlook expresses a near normal to 33 to 40 percent chance of above normal precipitation. && .AVIATION... 18Z Update: VFR conditions will prevail across interior central California for the next 24 hours. && .AIR QUALITY ISSUES... ISSUED: 03/20/2025 14:13 EXPIRES: 03/21/2025 23:59 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...SM aviation....SM weather.gov/hanford