Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
368 FXUS66 KSTO 152032 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 132 PM PDT Mon Jul 15 2024 .SYNOPSIS... Isolated (10-30%) chance of showers/t-storms today along the Sierra Crest, mainly south of I-80. Less hot weather is expected through mid-week with Moderate to Minor HeatRisk over the region. Temperatures begin to trend up again late in the week. && .Key Points... - Less hot through the middle of this week; warming trend by the weekend. - Isolated mountain showers/thunderstorms (10-30% chance) today along the Sierra Crest south of I-80 && .Discussion... Cooler high temperatures are expected around the area today, as onshore flow returns. Weak troughing along the coast is responsible for the slight cool down, and residents of areas under the influence of the Delta breeze will continue to see cooler high temperatures through Wednesday. Another push of monsoonal moisture is expected today, which will bring another chance of isolated (10-30% chance) showers and thunderstorms along the Sierra Crest, with the best chances for storms south of I-80. Forecast soundings once again show mid-level moisture with storm motions mainly towards the north-northeast. At the time of this writing, we are seeing some returns on radar mostly south and east of our area in Tuolumne County, moving towards the northeast. Some flashes of lightning have been observed with a cell currently in northwestern Plumas County, just west of Chester. Main threats with any storms that develop will be lightning, gusty winds, and small hail. Weak troughing off the West Coast will continue to promote cooling, which will help keep temperatures closer to normal, with highs in the mid 80s to around 103 through Thursday. Tuesday looks to be the coolest day, then we slowly warm back up as we move into Thursday. Upper level ridging looks to reamplify near the Four Corners region on Thursday and retrograde towards the west. The strengthening ridge will help temperatures climb around 3 to 5 degrees around the region on Thursday. Moderate HeatRisk will return Thursday, after remaining in Minor HeatRisk on Tuesday and Wednesday. && .EXTENDED DISCUSSION (Friday THROUGH Monday)... Upper-level ridging in the Four Corners region will continue to retrograde westward towards the coast and strengthen as we move into Friday. CLuster analysis reveals good agreement of the ridge deepening and moving towards the west. A return of widespread upper 90s to 100s for the Valley on Friday through Monday appears more and more likely. The National Blend of Models (NBM) advertises around a 60-100% probability of exceeding 100F during the extended period. The Northern Sacramento Valley will once again be the warmest, with highs potentially break the 110 mark on Monday. HeatRisk will remain in the Moderate category through Sunday, then an increase into Major HeatRisk on Monday. Monsoonal moisture may once again try to creep into the area Sunday afternoon and again on Monday afternoon and evening. The NBM is projecting around a 10-15% chance for some isolated showers/t-storms during the aforementioned timeframe, thanks to the potential monsoonal moisture intrusion. Some ensembles also suggest moderate PWAT values (100-150%) invading the Sierra Crest, so it will be something we keep an eye on as move through the week. && .AVIATION... VFR conditions across interior NorCal over the next 24 hrs. There is a 10-20% probability of isolated afternoon/evening thunderstorms over the Sierra. Surface winds will be mostly under 12 kts, except in the vicinity Delta, where west-southwesterly winds sustained 15-20 kts with gusts up to 25 kts through 15z Tuesday are expected. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$