Expires:No;;795051 FXUS66 KSTO 042205 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 205 PM PST Sun Jan 4 2026 .KEY MESSAGES... - Major mountain travel impacts above 5000 feet this through Monday. - Moderate to heavy rain will lead to urban and small stream flooding through Monday afternoon - Drier weather on Tuesday, with another round of showers and mountain snow mid-week. && .DISCUSSION... ...Today through Monday... Current radar shows moderate to heavy rain continuing to move through southern Sacramento Valley and northern San Joaquin valleys this afternoon, resulting in local urban and small stream flooding especially around the Sacramento Metro Area. Rain will continue to be moderate to heavy at times into the early evening, before moving out of the Valley into the foothills and mountains later this evening. Thunderstorm chances persist this afternoon but a lack of sufficient low level shear may work against convective initiation. Hires models are picking up on embedded areas of heavier precipitation further south along the Sierra foothills and a more robust appearance of the Shasta County Convergence Zone this afternoon compared to yesterday where MU CAPE values are close to 500 J/kg. The heaviest snowfall is expected this evening, with hourly rates 1 to 2 inches at times I-80 southward. Snow levels are around 5000-6000 feet this afternoon, before lowering to 4500-5000 feet Monday morning. Heavy snow is expected over the Sierra and highest peaks for the southern Cascades and Coastal Range. Hourly rates over the Sierra could approach 1 to 2 inches at times this evening. Additional snow accumulations of 4 to 8 inches above 4500 feet, with 1 to 2 feet above 5000 feet, and 2 to 3 feet above 6000 feet. Locally higher amounts at highest peaks. Winds gusting as high as 55 mph will help create near white out conditions within the mountains. Travel could be very difficult to impossible through passes into Monday. A Winter Storm Warning is effect for the Sierra above 5000 feet through Monday for the heavy snow and strong winds. If you plan to travel make sure you have alternate routes, backup plans, and carry a safety kit with you at all times. A brief period of drier conditions will return to the Valley tonight before the second wave of precipitation arrives early Monday morning. Latest model runs depict more prominent ridging building over the Great Basin which will help keep the main moisture plume and heavier precipitation north of US 50. Lighter rain and mountain snow accumulations are expected generally south of US 50 tomorrow compared to today. ...Tuesday through Wednesday... Dry conditions are expected Tuesday morning and afternoon, before another system starts to shift near the region. Guidance struggles with the development, track, and strength of the system, but the bulk of precipitation is favored over Shasta County, the foothills, and the mountains with lighter accumulations in the Valley. ...Thursday Onward... Long range guidance hints at a quieter offshore flow pattern setting up as ridging builds over NorCal. This will lead to the potential for fog and low cloud development across the Valley. Drier and warmer conditions are favored for areas above 1500 feet as the inversion sets up. && .AVIATION... Rain will continue through the TAF period, with isolated to scattered coverage this afternoon and evening. Widespread rain chances overnight and into tomorrow morning. Winds will be breezy at times from the south at 5-15kts, with gusts up to 25kts. Visibilities will fluctuate between 2SM and 6SM around rain. Ceilings will be IFR in heavier pockets of rain, but otherwise MVFR. Continued chances for rain post TAF period. && .STO WATCHES/WARNINGS/ADVISORIES... Flood Watch through Monday afternoon for Central Sacramento Valley-Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley- Northern Sacramento Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley. Winter Storm Warning until 4 PM PST Monday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$