Winter Storm in California, April 11, 2022

Area Forecast Discussion
National Weather Service Sacramento CA
157 AM PDT Mon Apr 11 2022

.SYNOPSIS...
Valley rain showers and accumulating mountain snow return to the
region today, along with breezy winds and much colder
temperatures. Additional rain and mountain snow chances for the
second half of the week.

&&

.DISCUSSION...
The dry, northerly winds are a thing of the past for most of
northern California. Late Sunday afternoon/evening, the
north/northwest winds switched and become more west/southwest, and
even southeasterly for some locations at this hour. Accompanying
this wind shift is more surface moisture. Sacramento International
Airport's dewpoint at 1 AM Sunday was a mere 14 deg F, now it is
39 deg F.

The much-discussed incoming system is right on our doorstep. As
of the publication of this forecast discussion, the precipitation
band is nearly into Shasta County, and will gradually advance
south/east through the rest of the region today. Winds will
increase through the day, initially southerly, then switch to
become west/northwest. This wind shift will reintroduce strong
gusts for some areas, notably for the mountains as well as
locations below west-wind-prone gaps in the northwestern
Sacramento Valley adjacent to the Coastal Range. Gusts are
expected to remain below Wind Advisory criteria, but can't rule
out a periods with gusts around 35 mph in portions of Shasta,
Tehama, Glenn, and Colusa Counties. Winds in the higher elevations
will be even stronger, possibly approaching/exceeding 60 mph at
the exposed peaks.

Best precipitation chances with highest QPF forecast will be in
the mountains where enhanced orographic lift will be realized.
Radar may end up looking more impressive than reality for the
Valley this morning as the atmospheric layer just above the
surface between the ground and cloud may be a tad too dry support
stratiform precipitation (i.e., virga). Best potential for
precipitation the Valley will be from scattered convective showers
and isolated thunderstorms. SPC Day 1 outlook paints nearly the
entire region under general thunder risk. Convective-allowing
models suggest around 100-250 J/kg surface-based CAPE which would
support some isolated thunderstorms. Main threat would be small
hail and heavy downpours. As is with scattered convection, rain
totals will range from nothing to around 0.10" in the Valley,
locally higher in stronger showers/thunderstorms.

Mountain snow levels will start out around 4000 to 5000 ft with
this storm, then lower in the afternoon. Expect around 3 to 6
inches in the Coastal Range and Shasta County, increasing to 6 to
14 inches in the southern Cascades and northern Sierra, and
localized 18 inch totals south of I-80 at peak-level. Latest WPC
guidance has been a bit more bullish compared to the operational
National Blend of Models. Official forecast follows the WPC
guidance with snow totals generally falling on the higher end of
the above ranges.

Precipitation chances drop off quickly after sunset today with
clearing skies overnight. Tuesday morning will start off cold with
some areas in the Valley approaching the freezing mark or lower.
Coldest Valley communities around sunrise will be around Redding
where 30-32 deg F is a possibility. National Blend of Models
gives Redding Airport a 70% chance of hitting 32 deg F and a 60
percent chance of hitting 30 deg F. Taking into consideration the
recent weeks' warm weather and the growing season upon us, will
issue a Freeze Watch for the northern Sacramento Valley. Valley
locations south of the Freeze Watch will also be cold with
widespread middle/upper 30s likely, even for Sacramento.

Cool and mostly dry conditions will prevail through mid-week. Any
precipitation chances through Wednesday will be generally limited
to the northern quarter of California, including parts of Shasta
and the southern Cascades. The next system that will bring renewed
precipitation chances to most of the region will be on Thursday
as a subtropical moisture tap arrives to the coast. Main impacts
will again be in the form of mountain snowfall as the Valley
appears to be on track for generally light rain amounts.
Precipitation chances will continue on Friday/Saturday; more
details in the extended discussion. // Rowe

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
Wet weather looks to continue Friday into Saturday as another
Pacific frontal system moves through. Snow levels are expected
around 4500 to 5500 feet Friday lowering to 3500 to 4500 feet
Friday night into Saturday. Additional significant amounts of
mountain snow expected with travel impacts possible. Drier weather
forecast Sunday into Monday with high temperatures warming to
above normal as EPAC ridging builds inland.

&&

.AVIATION...
Areas MVFR/IFR over intr NorCal til abt 06z Tues with lcl LIFR
omtns as Pac storm moves thru. Snow lvls 3500-4000 ft lwrg to
2500-3500 ft this aftn. In Cntrl Vly, areas of Sly sfc wind gusts
up to 35 kts poss ahd of fnt bcmg NWly behind fnt. Over hyr trrn,
areas W-NW sfc wnd gusts up to 50 kts poss.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM early this morning to 8 PM PDT
this evening for Burney Basin / Eastern Shasta County-Mountains
Southwestern Shasta County to Western Colusa County-Shasta Lake
Area / Northern Shasta County-West Slope Northern Sierra Nevada-
Western Plumas County/Lassen Park.

Freeze Watch from late tonight through Tuesday morning for
Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-
Shasta Lake Area / Northern Shasta County.

&&