Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
370 FXUS66 KSTO 302209 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 209 PM PST Thu Jan 30 2025 .SYNOPSIS... Active weather returns Friday and continues into next week with extended periods of moderate to heavy rain, mountain snow, and breezy southerly winds. A colder storm could bring heavy snow and travel impacts to the mountains next week. && .DISCUSSION... GOES West visible satellite imagery is showing mostly clear skies across interior NorCal this afternoon, but that will be changing soon. A major pattern change arrives overnight and continues into next week, as an atmospheric river brings subtropical moisture to California in a couple of waves. Precipitation begins late tonight in the Coastal Range, then steadily spreads east into the northern Sacramento Valley in the early morning, and the remainder of the Valley in the following hours. Valley rain totals for the first part of the system have trended slightly lower, while rain totals at higher elevations have trended slightly higher. Highest rain amounts are still expected to be centered around the I-80 corridor. The National Blend of Models (NBM) has 30 to 50% probabilities of 1.5 inches or more of rain in the majority of the Valley and 60 to 90% of 2 inches or more of rain in Shasta County, the foothills, and the mountains below snow level. Moderate to heavy rain rates will bring rises in area streams and rivers, along with nuisance flooding in low lying locations and roads. To this point, we have issued a Flood Watch for areas below 3000 feet from Friday afternoon through Sunday evening. Heaviest rain is expected from Friday afternoon through Saturday morning. This system remains fairly warm, with snow levels rising from around 5000 feet on Friday morning, to 6000 to 7000+ feet Friday evening. Most snow accumulations are still expected to remain above 7000 feet. The NBM has a 50 to 80% chance of snow totals of 6 inches or more above 7000 feet, with totals up to 2 feet possible over the highest peaks. Highest snow rates with this first system will occur Friday night and into Saturday, but snow will continue through the weekend and into next week. Additionally, gusty winds are expected in the mountains, generally up to 40 mph in most locations above 6500 feet, and up to 60 mph over the highest peaks. With all of this in mind, we have issued a Winter Weather Advisory for areas above 6500 feet in the Sierra and southern Cascades from 4 AM Friday to 4 AM Sunday. Travel impacts are likely across interior NorCal on Friday and over the weekend, so be sure to check road conditions at quickmap.ca.dot.gov and weather conditions at weather.gov before heading out the door! && .EXTENDED DISCUSSION (Monday THROUGH Thursday)... Cluster analysis and ensembles continue to show active weather continuing through much of next week. Currently, the NBM is showing a 50 to 80% probability of 2 inches or more of rain across interior NorCal from Monday through Thursday (slightly lower, 20 to 30% in the northern San Joaquin Valley). This system will also be colder than the one that occurs over the weekend, with the NBM currently advertising a 30 to 60% chance of 6 inches of snow or more between 3000 and 5000 feet, and a 50 to 90% chance of 24 inches or more above 5000 feet. Higher amounts are possible across highest peaks. Periods of gusty southerly winds are also expected to continue through Wednesday. There is still some uncertainty in the exact trajectory of the main plume of moisture in this second wave of weather though, so exact rain and snow totals, as well as the timing of heaviest precipitation are uncertain. Be sure to prepare now for the continued wet and wintry weather! Stay up to date with the forecast at weather.gov as we get closer. && .AVIATION... Mainly VFR conditions are expected across interior NorCal until an unsettled weather pattern brings precipitation, resulting in MVFR/IFR conditions starting in the Coastal Range and spreading eastward starting 16Z Friday. Snow levels are expected to start around 5,000 feet, then increase to 6000 to 7000+ feet by 18z Friday. MVFR/IFR and local LIFR conditions are possible in the northern San Joaquin Valleys in BR/FG from 06Z to 18Z Friday as precipitation moves into the area. Southern to southwestern winds over the mountains are forecast to be 15-20 knots with gusts up to 40 knots by 14Z Friday. Southern surface winds in the Valley and foothills are expected to be around 15 knots with gusts around 25 knots by 16Z Friday. && .STO WATCHES/WARNINGS/ADVISORIES... Flood Watch from Friday afternoon through Sunday evening for Carquinez Strait and Delta-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. Winter Weather Advisory from 4 AM Friday to 4 AM PST Sunday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$