Severe Thunderstorm Warning 4, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
254 PM PST Mon Mar 6 2023

.SYNOPSIS...
Active weather pattern through Wednesday will bring additional
rounds of snow over the foothills and mountains and scattered
Valley showers. A wet, warm storm system late this week into the
weekend will bring higher elevation snow along with moderate to
heavy rain to the Valley and foothills with local flooding impacts
of small creeks and streams possible.
&&

.Discussion...
After a brief break in rain and snow showers overnight, radar is
showing snow began again over the Sierra, Coastal Range, and
Shasta County mountains this morning with scattered showers
across the Valley. A longwave trough sitting along the PacNW and
northern California coast will remain through midweek, with
multiple shortwaves moving along the flow. One wave is what has
brough a return of showers today into tomorrow with another wave
producing another shot of moderate to heavy mountain snow tomorrow
evening into Wednesday morning. An additional 1 to 1.5 feet of
snow is forecast over the Sierra today and another 1 to 2 feet of
snow expected tomorrow through Wednesday. Low snow levels remain
through Wednesday, down to 2500 feet over the Sierra and 1000 to
1500 feet over Shasta County and the southern Cascades. In the
morning hours tomorrow, light snow is possible down to the Valley
floor in Tehama and Shasta counties, though accumulation will be
limited. Isolated thunderstorms are also possible across the
Valley today and tomorrow in the afternoon and evening hours with
CAPE values are forecast around 100-400 J/kg. Highest instability
and therefore best chances for thunderstorms are today. Tomorrow,
best chances will be in the northern Sacramento Valley.

Cool temperatures will continue into late week as the current
longwave trough continues to bring cold air into northern
California. Valley and foothill high temperatures will be in the
high 40s to mid 50s. Thursday morning is forecast to be the
coolest with Valley temperatures near freezing. A brief break in
precipitation is expected late Wednesday into much of Thursday
before the next major storm is slated to impact northern
California later Thursday into the weekend. More details in the
extended forecast. -HEC

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...
Confidence is increasing for a warmer storm to move through
interior northern California later this week and over the weekend
as ensemble guidance and cluster analysis come into better
agreement. This storm is trending warmer than the most recent
winter storm, with snow levels expected to be much higher.
Additionally, the Extreme Forecast Index is highlighting most of
interior NorCal for anomalous wind speed and wind gusts for
Friday, as breezy south to southwest winds develop with this
system. Precipitation first moves in late Thursday, and spreads
inland Friday through Sunday, with the heaviest amounts expected
on Friday. The National Blend of Models (NBM) has snow levels
initially starting off around 3000 to 5000 feet Thursday night,
but quickly rising up to 6000 to 8000 feet on Friday. Snow levels
lower slightly over the weekend back to around 5000 to 7000 feet.
At this point, storm total precipitation from WPC is looking like
1 to 3 inches in the Valley and 2.5 to 6 inches in the foothills
and mountains ending early Monday. This will not be a repeat of
the 1997 flooding as this storm is not as strong or as warm. The
main impacts with this storm will be confined to slick roads,
rises on small creeks and rivers from rain and snow melt mainly
below 5000 feet, and local ponding of water on roadways. Unsettled
weather looks to continue into early next week with additional
rounds of precipitation possible through the middle of next week,
however confidence is much lower that far out in time. &&

.AVIATION...
Weather system is bringing scattered rain showers across the
Valley and snow showers over the mountains and foothills through
Tuesday morning. In the Valley, VFR conditions expected next 24
hours except for local MVFR in isolated thunderstorms through 03z
Tuesday. Also, isolated MVFR/IFR conditions in the northern
Sacramento Valley due to low ceilings/visibility through Tuesday
morning. Over the mountains and foothills, areas of MVFR/IFR with
local LIFR due to snow and rain showers. Surface winds generally
less than 12 kts with gusts up to 30 to 40 kts in the mountains.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 10 AM PST Wednesday for Shasta
Lake Area / Northern Shasta County.

Winter Weather Advisory until 10 AM PST Wednesday for Burney
Basin / Eastern Shasta County.

Winter Weather Advisory until 10 AM PST Wednesday for Mountains
Southwestern Shasta County to Western Colusa County.

Winter Storm Warning until 10 AM PST Wednesday for Motherlode-
Northeast Foothills/Sacramento Valley-West Slope Northern Sierra
Nevada-Western Plumas County/Lassen Park.

&&

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