July 29, 2021 - The National Weather Service Hanford Office reports scattered thunderstorms will develop over the Sierra Nevada by early Thursday afternoon and linger into the evening hours.
In addition to dangerous cloud to ground lightning, a few thunderstorms will bring small hail, wind gusts to about 40 mph and heavy rain with the potential for flash flooding.
Hikers should be prepared to seek a safe place when skies turn ominous and thunder is heard.
Area Forecast Discussion National Weather Service Hanford CA 1239 PM PDT Thu Jul 29 2021 .SYNOPSIS... Slightly warmer than average high temperatures look likely into the foreseeable future over the forecast area. Monsoonal moisture will provide the Sierra Nevada with a chance of afternoon and evening thunderstorms each day until Sunday. && .DISCUSSION... Weak upper level troughing over the eastern Pacific centered several hundred miles west of the Point of Conception coupled with broad ridging centered over the Plains states is allowing a steady stream of mid to high level tropical moisture to stream north to northwestward into the forecast area. This moisture stream was responsible for yesterdays thunderstorms over the Sierra and for the current showers with embedded thunderstorms into this afternoon. This pattern has also kept the synoptic temperatures pretty steady over the last several days and will do so through at least Saturday. A stronger surge of moisture will advect into the region tomorrow and this will not only increase the chances of thunderstorms but also increase the potential rainfall amounts possible with any of the given thunderstorms that do develop. The highest likelihood of thunderstorms will be for the higher elevations of the Sierra Nevada but a few thunderstorms over the Kern County Mountains and Deserts would not be out of the question each afternoon through Sunday. However, the chances for the larger precipitation amounts with thunderstorms will be greatest for the higher elevations. With this reasoning in mind a Flash Flood Watch for above 5000 feet has been issued for the Sierra Nevada from Yosemite southward to parts of the Kern County Mountains around Tehachapi. This watch will begin at Noon Friday through 8 PM Saturday night. Hikers and Campers venturing out to these areas should stay aware of any changes in the weather and remember to never set up a campsite in a low lying area as heavy rainfall in higher elevations can quickly flood those areas with little notice from a distance. Besides the heavy rainfall threat, thunderstorms will also bring strong gusty winds, small hail, and of course dangerous lightning. By early Sunday, troughing to the west will push eastward and this will redirect the monsoonal moisture flow further eastward and allow ridging to begin building into southern California. This will bring slightly warmer temperatures and allow drier weather to return to the region with a more southwesterly flow aloft at least through Thursday. && .AVIATION... Mountain obscurations in showers and scattered thunderstorms possible over the Sierra through 03Z Fri and again after 19z Friday. Otherwise, VFR conditions will prevail through the next 24 hours. && .AIR QUALITY ISSUES... On Thursday July 29 2021... Unhealthy for sensitive groups in Fresno... Kern... Madera... Merced and Tulare Counties and Sequoia National Park and Forest. Further information is available at Valleyair.org