Includes Eastern Mariposa and Madera Counties and Yosemite National Park
Deadly lightning, brief downpours, small hail, and wind gusts near 40 mph will be possible. If you hear thunder, go indoors.
Area Forecast Discussion National Weather Service Hanford CA 132 AM PDT Mon May 17 2021 .SYNOPSIS... Showers and thunderstorms are possible again this afternoon over the Sierra Nevada as instability aloft remains in place. Brief warming trend through Tuesday as high pressure builds. A slow moving trough will impact the region later in the week, sending afternoon high temps down into the mid 70s. Afternoon highs should rebound by the weekend as the trough slowly weakens and exits the area. && .DISCUSSION... Another round of afternoon thunderstorms is in store for the Sierra Nevada and adjacent foothills this afternoon as instability on the backside of the trough remains over the area. However, areal coverage may not be as large as yesterday due to the trough exiting the area with shortwave high pressure moving in. Afternoon highs will rise several degrees today from yesterday`s highs as a result of the building ridge. The ridge axis will be directly overhead by Tuesday afternoon, so expect highs to rise a bit again, likely into the upper 80s for most of the San Joaquin Valley and low to mid 90s across the Mojave Desert. By Tuesday night, a trough of low pressure will dig southward from Western Canada and will begin impacting the area Wednesday, which will lead to a period of breezy conditions in the wind-prone areas of the CWA through Friday. Afternoon highs will drop accordingly as the trough approaches, and NBM guidance is forecasting highs ranging from 77-83 degrees for the valley, with the upper 70s occuring in Merced County. Increasing onshore flow overnight Wednesday and lowering 500 mb heights will send afternoon highs into the low to mid 70s for the valley for Thursday, which will be around 5-10 degrees below average for this time of the year. The upper low is forecast to meander southward on Friday, with the cold core likely centering over central Nevada. This will give a bit of a boost to the instability over the mountains due to the cold air aloft being closer in proximity to the Sierra Nevada, so afternoon thunderstorms are possible in the mountains Friday. A bit of a blocking pattern will prevent the trough from quickly leaving the area on Friday and Saturday, so expect a slow rebound in afternoon high temperatures over the weekend. On Sunday, EPS and GEFS guidance is showing the upper trough weakening and opening up into an open wave. It is then forecast to exit the area Sunday afternoon or Sunday night, which will allow for a bit of a warm up early next week. Blended model guidance is showing highs around 90 for next Monday, however this is subject to change some as there is some uncertainty in just how long the trough takes to leave the area on Sunday.Source: NWS
