Widespread rain later this afternoon through Monday, with lingering mountain showers on Tuesday. Isolated thunderstorms possible through Tuesday. Locally breezy northerly winds this afternoon and tonight, then breezy southerly winds Monday. Drier with a warming trend during mid-week.
Afternoon satellite imagery shows Tropical Storm Hilary’s center nearing SoCal, as well as extensive cloud cover across interior NorCal. Some light radar returns are being detected across portions of the Coastal Range and the Sierra south of Highway 50 this afternoon as moisture continues to advect northward.
HREF suggests the best potential for isolated thunderstorms will be over the Coastal Range and the Sierra south of Highway 50 this afternoon and evening. However, cloud cover could reduce thunderstorm coverage. If thunderstorms develop, main hazards will be brief heavy rain, gusty outflow winds, small hail, and lightning.
Increasing shower chances are expected later today into Monday from south to north as the upper low interacts with the eventual remnants of Tropical Storm Hilary, with the tropical system eventually tracking through Nevada late tonight into Monday per latest National Hurricane Center guidance. The EFI continues to highlight the anomalous QPF nature of this event. WPC guidance indicates generally light precipitation amounts with less than 0.25 inches for the Valley and 0.50-1.00 inches over the mountains. Locally heavier amounts will also be possible where thunderstorms develop.
Latest HREF guidance suggests thunderstorm development across portions of the southern Sacramento Valley, northern San Joaquin Valley and adjacent Sierra foothills Monday afternoon as instability develops.
There will still be a few lingering showers over the mountains on Tuesday. Otherwise, drier and warmer conditions are expected by mid-week, with widespread 90s in the Valley highs by Wednesday.
Locally breezy north to east winds develop later this afternoon into the overnight hours along the west side of the Sacramento Valley and adjacent terrain, with gusts up to 15-25 mph. These winds may push some wildfiresmoke into portions of the northern Sacramento Valley tonight. Then, breezy southerly winds develop in the Valley on Monday as pressure gradient tightens, with gusts up to 20-30 mph.
Extended Discussion (Thursday through Sunday)
Cluster analysis and model ensemble guidance project an upper level trough over the Eastern Pacific Thursday, deepening into the weekend, as a westward building Central CONUS high approaches the desert southwest. This will strengthen the southwesterly flow pattern over the region heading into the weekend.
Increased heights keep Thursday’s Valley high temperatures in the mid- to upper 90s. The National Blend of Models (NBM) indicates a gradual cooling trend heading into the weekend where max high temperatures will be 5-10 degrees cooler; southwesterly winds through the Delta will promote additional cooling. Predominantly dry conditions are expected through the period as lingering moisture remains east of the Sierra Crest.