588
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.
&&
$$
