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Area Forecast Discussion · National Weather Service Sacramento (STO) · issued Friday, November 13 at 2:28 AM PST.
Messages
A pair of storm systems will bring widespread rain, moderate to heavy rain and snow in the mountains, and gusty to strong southerly winds today into Monday
The first storm begins today and continues into early Saturday and will be the stronger system in terms of winds and heavy snow. After a lull during the day Saturday, the second storm arrives Sunday and continues into Monday
Winter Storm Warning in effect from 10 AM PST this morning through 10 AM Saturday morning for the Sierra and Lassen Volcanic National Park above 6000'
Wind Advisory is in effect from 4 am to 7 pm PST today for the Sacramento Valley and Delta
Flood Advisory until 4 PM this evening for low-lying areas along the Delta and vicinity, with coastal flooding potential from high tides
Another storm will bring the potential for additional rain, mountain snow and gusty winds mid to late next week
Discussion
The first of several storm systems moves into the region today and continues through Saturday morning bringing moderate to heavy mountain snow, widespread rain, thunderstorms and windy conditions to the region. Rain is gradually moving into the area and will spread across the region this morning and coverage will only increase as we move throughout the day. Heavy rainfall rates are possible with stronger thunderstorms. Latest CAMS models are showing potential for a line of thunderstorms in the morning, with additional potential in the afternoon and early evening hours. Coverage of rain starts to diminish in the overnight hours, with isolated to scattered chances within the mountains and isolated within the Valley. Total forecast rainfall with this first storm is 0.25" to 0.75" in the Valley and Delta, up to nearly 3 inches in the mountains and foothills. Isolated higher amounts are possible especially where stronger thunderstorms develop. The latest the blend-of-models forecast shows a 10-15% Chance of thunderstorms this morning, a 15-25% chance of thunderstorm development this afternoon and evening. There is quite a bit of shear, both low and mid level, so there is some potential for severe storms. Impacts from stronger storms would be heavy rainfall rates with ponding of water on roads, frequent lightning, gusty winds, and small hail, as well as gusty winds.
In addition to gusty winds possible with thunderstorms there will be strong southerly winds that peak later this morning and early afternoon. Winds were already beginning to increase over the northern Sacramento Valley early this morning, with gusts to 25 to 35 mph by 2 AM PST. A Wind Advisory is in effect for the Sacramento Valley and Delta from 4 AM this morning through 7 PM this evening. Gusts up to 35-45 mph are expected within the Advisory area, with the strongest winds expected over the northern Sacramento Valley. There is even a locally 60-80% chance of winds greater than 45 mph in the vicinity of Red Bluff and just to the east. Strong winds are expected over the mountains as well, with gusts up to 60 mph. Downed tree branches and localized power outages are possible.
Mountain snow will be heavy at times above 6000 feet, combining with the strong winds to create significant reductions in visibility, with near whiteout conditions possible. Travel could be difficult during this time, impacting mountain travel this evening and into early Saturday. Total snow accumulations of 6 to 12 inches are expected, with up to 18 inches at the highest peaks. Minor accumulations of up to an inch are possible down at 5000 feet. The heaviest snow is expected late this morning into the evening hours, with a period of heavy snow with intensity to around 2" an hour at times, when associated with convective storms. Snow levels will be 6500-7500 ft today and drop to 5500-6000 feet by Saturday morning. A Winter Storm Warning remains in effect from 4 AM this morning through 10 AM Saturday for the northern Sierra above 6000 feet, including Highway 50, I-80, the southern Cascades, and Lassen Volcanic National Park. A lull in activity is expected Saturday afternoon and evening as the first system moves out of the region, with mainly just some lingering showers.
A Flood Advisory remains in effect until 4 PM this evening for low-lying areas along the San Pablo Bay, Carquinez Strait, and Suisun Bay shorelines in Solano County, as well as low-lying areas along the Sacramento River, San Joaquin River, and other Delta waterways. This is due to the potential for coastal flooding from high tides.
A lull in activity is expected Saturday afternoon/evening, with storm number 2 moving in Sunday and continuing into Monday. Precipitation spreads into the west in the morning with coverage becoming widespread by Sunday afternoon. Rainfall may be moderate at times within the mountains, foothills, and Valley. Coverage will start to diminish along with rain intensity as we move into Monday. Precipitation chances in the Valley start to clear by the afternoon and evening, with lingering precipitation in the mountains ending early Tuesday morning. WPC guidance has trended slightly lower, indicating precipitation amounts ranging from 0.25 to 1 inch in the Valley, with 0.75" to 1.75" over higher terrain. Snow levels during this time will around 6500-7500 feet Sunday afternoon and drop to around 5500-6500 feet Monday morning. Snow will be moderate at times and snow totals are expected to be less with this second storm, with a 50-75% chance of seeing at least 6 inches of snow over the Sierra (highest chances south of Highway 50). Heaviest snow is expected late Sunday night into early Monday morning. Slippery roads as well as some reductions in visibility are possible at times, bringing travel delays.
Another lull in activity is expected Tuesday morning and afternoon. There is a potential for an additional system mid to late next week bringing more precipitation to the area. While uncertainty continues with the timing, development, and strength of these systems, recent trends are showing potential for another wet system with widespread rain, impactful mountain snow and gusty winds. Stay tuned to see how the forecast develops!