Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
341 FXUS66 KSTO 132128 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 228 PM PDT Sat Jul 13 2024 .SYNOPSIS... Hot weather continues today with Major to Extreme HeatRisk persisting across much of the region. Elevated fire weather conditions will also continue. Isolated shower and thunderstorm chances thru Sunday, mainly near the Sierra crest. Not as hot beginning Sunday and into next week. && Key Points - Long-duration, dangerous heat event persists today, then not as hot into the middle of next week. - Isolated showers/thunderstorms thru the weekend, mainly along the Sierra Crest. - Red Flag Warning for Sierra Fire Zones 221 and 269 at elevations greater than 6000 feet and (new) for the Coastal Range Fire Zones 213, 263, 279. .Discussion... Current RADAR shows scattered elevated showers making their way across interior NorCal, with an area of elevated convection attempting to become more organized just southwest of Tuolumne County (as of 1:56 PM). Elevated monsoonal moisture continues to make its way over California bringing increased risk of isolated afternoon/evening showers/thunderstorms today through Sunday. The highest coverage and NBM probabilities are along the Sierra crest (20-40%) with generally southerly steering flow. Given how this is following a prolonged heat event and the risk for dry thunderstorms, a Red Flag Warning remains in effect for the Sierra zones (above 6000 ft) through 8 PM Sunday. Over the Coastal Range, the NBM indicates 10-20% chance for isolated showers/thunderstorms tomorrow, so the Fire Weather Watch has been upgraded to a Red Flag Warning which will go into effect 2 AM Sunday and last through 11 PM that night. Elsewhere, some sprinkles or light showers will be possible in the Valley. The monsoonal moisture is expected to move out of the area early next week with a few lingering thunderstorm chances on Monday afternoon/evening, roughly 10-20% chance along the Sierra. Ensembles depict the trough offshore remaining off the coast for the short-term forecast period which will reinforce a slight cooling trend tonight and into next week as widespread moderate HeatRisk returns to interior NorCal. As a result, our heat products (Excessive Heat Warning/Heat Advisories) are on track to expire at 9 PM this evening. Onshore flow is also set to increase as a more pronounced Delta breeze returns with 20-30 mph gusts in the afternoon/evening aiding in overnight relief. && .EXTENDED DISCUSSION (Wednesday THROUGH Saturday)... Cluster analysis of the ensembles for the middle of next week places the upper-level ridge over the Four Corners region with a trough approaching the Pacific Northwest. This places northern California under southwesterly flow with temperatures forecast to be near their middle July normals. Temps will begin a warming trend for Thursday as the Four Corners high builds westward. By Thursday the probability of hitting 100 deg F rises to 60-80% for the northern Sacramento Valley. These probabilities will only increase by Friday and Saturday with widespread triple digits becoming likely for most Valley communities. // Rowe && .AVIATION... VFR conditions are forecast to prevail over interior northern California over the next 24 hours. Isolated showers and thunderstorms possible over the Sierra Nevada. Winds generally at/below 15 kt in the Valley; exception in the vicinity of the Delta with winds 15-25 kt and gusts to 35 kt. && .STO WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 9 PM PDT this evening for Central Sacramento Valley-Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley- Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley. Red Flag Warning from 2 AM to 11 PM PDT Sunday for Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-Northern Sierra Including the Tahoe and ElDorado NF/S West of the Sierra Crest-Southeast Edge Shasta-Trinity NF and Western Portions of Tehama-Glenn Unit-Stanislaus NF West of the Sierra Crest. Heat Advisory until 9 PM PDT this evening for Burney Basin / Eastern Shasta County-Carquinez Strait and Delta-West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$