000
FXUS66 KSTO 222214
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
314 PM PDT Wed Mar 22 2023


.SYNOPSIS...
The abnormally cool and unsettled weather pattern continues into
next week with occasional showers and mountain snow. Areas of
morning frost will be possible beginning Friday through the
weekend.
&&

.Discussion...
The low pressure system currently spinning south of Santa Cruz area,
is beginning to weaken as it slowly progresses south and east. As
this low decays, lingering showers have continued to rotate around
the circulation, keeping isolated to scattered showers in the
forecast through at least this evening.

Upstream, two weak shortwaves will move through NorCal tonight and
later Thursday, allowing more snow showers to develop across the
Sierra tonight through early Friday morning. Snow levels will
generally be 4000-4500 feet, with total snow accumulations of 5 to
10 inches, locally up to 12-14 inches near the peaks. Given the
lower snow levels and already significant heavy snow load, issued a
low-end Winter Weather Advisory for elevations above 4000 feet in
the Sierra. Outside of snow, a brief period of isolated to scattered
showers will move through the northern Sacramento Valley late
afternoon Thursday, with better chances in the Motherlode of seeing
some light rain showers. Confidence is low, but some meager
instability is possible for a few hours tomorrow between 22-02Z, and
a thunderstorm is not out of the question if a stronger storm
develops between Redding and Chico.

By Friday, we`ll be under mostly dry northwesterly flow, keeping
much of the region dry. Another shortwave will brush across NorCal
bringing mainly more snow showers for the mountains over the
weekend.

Given we`ll be under cool, northwesterly flow, temperatures will
be abnormally cold starting Friday morning, with Valley low
temperatures near or slightly below freezing each morning through
Sunday. Coldest morning will be Sunday. As a result, issued a
Frost Advisory for the impacts to the spring growing season.

//Peters
&&
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...


Our attention then turns toward a strong weather system expected
Monday-Tuesday. A low pressure system will drop from the Gulf of
Alaska and eventually become a closed low somewhere off the NorCal
coast early next week. As this low strengthens and digs off the
NorCal coast, broad upper-level lift will tap into some low-end
moisture, producing widespread precipitation and heavy mountain
snow. Clusters still indicate some variation in the location of the
low center, which would influence exactly how much winds and
precipitation we could see with this system. Even so, ensembles have
been fairly consistent on the timing in the last few model runs. Our
current forecast has storm total precip of 0.5"-1.25" in the Valley,
1-2" in the foothills, and 2-3" in the mountains. Snow levels will
be fairly low initially Monday morning at 1500-2500 feet, increasing
to 2,000-3,500 feet by Monday afternoon. Total snow amounts of 1-4
feet are possible for elevations above 3000 feet. The heaviest is
expected to be Monday night through Tuesday. In addition to
precipitation, we will also see some gusty winds as pressure
gradients tighten in response to the closed low, how strong those
winds will be is very unclear at this point given the variation in
the low center, but at least gusts to 30 mph appears likely for
portions of the region. Given the synoptic set-up, there will likely
be periods of thunderstorms possible sometime Tuesday as well, but
those details will become more clear the closer we get.

Ensembles are indicating the low will be slowly moving southeast
through the middle of the week, keeping some chances in the forecast
through much of Wednesday. There is still some discrepancies in the
timing of how quickly the low will move out, so confidence is fairly
low beyond Tuesday.

// Peters

&&

.AVIATION...


Lingering light showers will remain through at least tonight
across much of the region. Sacramento metro terminals will see
mostly dry conditions by late afternoon. Another weak weather
system will allow for some light showers mainly across the
foothills and briefly across the northern Sacramento Valley
tomorrow. Otherwise, snow showers will remain through early
Friday morning for the Sierra. Besides some lingering afternoon
breezes to 15-20 knots, winds will remain below 10 knots, with
mostly light winds remaining in the forecast by tonight. Periods
of MVFR conditions due to low ceilings from lingering stratus as
low as 2.5-3 Kft will remain through at least Thursday afternoon.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to 4 AM PST
Friday for Burney Basin / Eastern Shasta County-Shasta Lake Area
/ Northern Shasta County-West Slope Northern Sierra Nevada-
Western Plumas County/Lassen Park.

Frost Advisory from 3 AM Friday to 8 AM PST Sunday 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.

&&

$$