Includes Eastern Mariposa and Madera Counties and Yosemite National Park
May 15, 2021 - The National Weather Service Hanford Office reports isolated thunderstorms can be expected near the Sierra crest each afternoon and evening through Monday.
Small hail and wind gusts near 40 miles per hour are a couple of hazards associated with strong thunderstorms.
In addition to dangerous cloud to ground lightning strikes, any thunderstorm can produce intense rainfall rates, leading to localized flooding.
Area Forecast Discussion National Weather Service Hanford CA 250 AM PDT Sat May 15 2021 .SYNOPSIS... Increasing onshore flow today will lead to much lower afternoon highs compared to yesterday. Daily occurrences of afternoon showers and thunderstorms will be possible the next couple of days in the Sierra Nevada and foothills as the trough of low pressure moves overhead. A quick warm-up early next week will be followed by a cooldown as troughing resumes by next Wednesday. && .DISCUSSION... Onshore flow this morning is bringing breezy conditions through the passes of the west side hills and much cooler temperatures. This is occuring due to a trough of low pressure centered over northern California that is digging southward bringing westerly winds and marine-cooled air to the valley. NBM guidance is suggesting that afternoon high temperatures today will be as much as 10-12 degrees cooler today than yesterday due to the modified airmass. In the afternoon hours, an isolated chance of showers and thunderstorms will exist in the Sierra Nevada north of Madera County, but the bulk of the activity will likely remain north of our forecast area where the better dynamics will be. The trough will continue to move south overnight and we will get a slight chance of showers over the Sierra Nevada and foothills, with an isolated shower possibly eking into the eastern portion of the valley. Any rainfall totals with these showers Sunday morning would be limited. Greater coverage of convection in the Sierra Nevada and foothills by Sunday afternoon as the combination afternoon heating and better dynamic support arrives. Brief heavy rain, lighting, and gusty winds would be the main impacts of these storms on Sunday. Showers and thunderstorms may also make it into the Kern County mountains and desert (near Ridgecrest) by late afternoon on Sunday as the low`s center tracks further to the south. By Monday, the upper low will shift east and be centered over the four corners region. For us, that means a brief warm-up under shortwave ridging taking afternoon highs back into the upper 80s across the valley. The ridge axis will be directly overhead Tuesday, which will likely signal a quick return to 90 degree heat for the valley. However, this heat will be short lived as both the EPS and GEFS are forecasting another trough of low pressure to reach the area by Wednesday, perhaps bringing another round of light precip over the mountains and cooler weather to the valley. Cool weather is expected through the end of the next work week as the troughing persists.Source: NWS
