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000
FXUS66 KSTO 130838 AAA
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
125 AM PDT Sat Apr 13 2024

.Synopsis...
Widespread rain, light mountain snow, gusty winds today. Lingering
showers Sunday, then drier and warmer weather for all of next
week.

&&

.Discussion...
Weather system will bring minor impacts in the form of widespread
rain, periods of mountain snow, and gusty winds today.

The closed upper low currently spinning off the CA coast will
progress east-southeast throughout today, bringing widespread rain
and mountain snow showers. Current radar as of 12am continues to
keep a thin, light band of rain from Fairfield up to northern
Shasta County. Much of this band is not resulting in measurable
rain, with only some observations reporting rain in Shasta County
over the last hour. Looking at the latest hires models, only 1 or
2 are handling the current light rain bands, with some location
and timing discrepancies. Even so, all hires are in agreement on
the eventual evolution of a more defined band of precipitation
moving westward (associated with a cold front), filling in across
the Coastal Range- Bay Area- Central Valley between about
5am-8am. This band will bring widespread moderate to occasionally
heavy rainfall through this afternoon. Rainfall totals haven`t
changed much since the previous forecast, with Valley amounts of
0.25-0.75", locally to 1-1.50" across the eastern far southern
Sacramento Valley, San Joaquin Valley and surrounding foothills.

Instability won`t be great with heavy cloud cover, likely
limiting the widespread thunderstorm threat today. Even so, some
embedded vorticity waves may help to briefly enable some
occasional embedded lightning with the main band of precipitation
later this morning-afternoon. Latest RAP guidance is indicating a
600-700mb vort wave may briefly enhance precipitation in the
Delta-central Sacramento Valley areas, and again in the northern
San Joaquin Valley later this evening. In the event of any
embedded thunderstorms, the main threats would be brief heavy rain
and small hail.

Snow levels remain between 6500-7500 feet this morning and are
forecast to drop to around 4500-4000 feet behind the frontal
passage later this afternoon. Given the initially high snow
levels, snow impacts will be somewhat brief and limited to the
higher elevations (mainly above 6000 feet). The best upslope
enhancement will be focused south of Highway 50, mainly impacting
the southern Sierra. Even so, if driving across the Sierra this
afternoon, be prepared for brief periods of moderate snowfall with
rates generally around 0.50`/hr, though brief periods up to 1"/hr
will be possible as well. The heaviest snowfall along I-80 and
Highway 50 will be between 11am and 4pm today, with snowfall
totals of 1"-4". Higher snowfall amounts of locally up to 6-12" at
the highest peaks south of Highway 50.

In addition to precipitation, expect breezy to gusty south to west
winds today, strongest across the mountains from I-80 south, where
gusts to around 45mph may add to locally hazardous driving
conditions this afternoon. Gusty southerly winds generally to
25-30 mph will be possible in the Valley as well. Probabilities
of wind gusts greater than 40 mph are basically negligible today
in the Valley.

Cloudy skies will keep things cool, with cooler temperatures
following the cold front as well, with Valley temperatures staying
in the low 50s through this afternoon.

Besides some lingering, wrap-around light showers tomorrow as the
upper-low exits to the southeast, expect drier conditions. Dry
northwest flow Monday with increasing heights aloft will allow
temperatures to increase, rebounding to the mid to upper 70s for
the Valley by Tuesday.

//Peters

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Upper level ridging progged to be main synoptic feature through
the extended forecast period. This will result in dry weather over
interior NorCal with above normal temperatures. NBM showing high
temperatures 10-15 degrees above normal Wednesday through Saturday
with low to mid 80s in the Central Valley and mainly 60s and 70s for
the mountains and foothills. Locally gusty north to east wind
possible at times.

&&

.AVIATION...
Areas MVFR/IFR, with lcl LIFR over mtns, next 24 hrs in shra and
mtn shsn as Pac front moves inland today. Snow lvls above 6000 ft
this mrng lowering to 3500-4500 ft this evening. Isold -tsra
possible over E Shasta/W Plumas mtns til 03z Sat. In Central Vly,
areas Sly sfc wind up to 20 kts with lcl gusts to 30 kts possible
thru 03z Sat. Lcl SWly sfc wind gusts up to 40 kts possible over
SierNev.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$