209
FXUS66 KSTO 032056
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
156 PM PDT Fri May 3 2024


.SYNOPSIS...
DRY AND WARM WEATHER TODAY WITH LOCALLY BREEZY NORTHERLY WINDS.
ACTIVE WEATHER RETURNS THIS WEEKEND AS A WEATHER SYSTEM MOVES
INTO THE AREA BRINGING SHOWERS, MOUNTAIN SNOW, ISOLATED
THUNDERSTORMS, GUSTY WINDS AND MUCH COOLER TEMPERATURES.

&&

Sunny and pleasant conditions prevail across interior NorCal this
afternoon, with some breezy northerly winds being observed in the
Valley. Our next weather system is approaching the area from the
Gulf of Alaska and is expected to bring widespread rain showers,
mountain snow, isolated thunderstorms, gusty southwest winds, and
much cooler temperatures on Saturday.

Model guidance shows an anomalously deep and cold closed low
moving into the PacNW Saturday morning. Precipitation first looks
to begin in far northwestern California early Saturday morning
then spread inland throughout the day. Latest forecast rainfall
totals remain around 0.50" to 1.30" inches for the Valley and
around 1" to 3" inches in the foothills and mountains. With the
track of the low forecast to move over northern part of
California, there will be a risk of isolated thunderstorms to
develop Saturday afternoon and evening. There exists a 15-25%
probability of thunderstorm development, with the better chances
north of I-80. Any thunderstorms that do form could bring locally
heavy rainfall, dangerous lightning, gusty winds, small hail, and
possible funnel clouds.

The Winter Weather Advisory has been upgraded to a Winter Storm
Warning, with the timeframe remaining the same, from 11 AM
Saturday until 8 AM PDT Sunday. Snow, heavy at times, is expected
mainly for elevations higher than 5000 feet. Total snow
accumulations forecast are around 5 to 12 inches, with locally
higher amounts at the highest elevations. NBM probabilities of
exceeding 12" inches of snowfall are at around 60-80% along the
I-80 corridor. Winds will also be gusting from 30 to 50 mph out
of the southwest. Snow levels will be at around 4000-5000 feet
Saturday afternoon, and lower as the system moves through the area
to around 3000 feet on Sunday. Snowfall rates of 1-2" inches per
hour are possible, mainly from around 10 AM to 10 PM Saturday as
the bulk of the precipitation moves through. Snow covered roads,
reduced visibilities, and chain controls are all likely. If you
must travel this weekend, make sure to check road conditions at
quickmap.dot.ca.gov before heading out.

Gusty winds will also begin to develop later tonight through
Saturday as the system moves closer to the area. The NBM projects
around a 55-90% probability of wind gusts greater than 40 mph in
the northern/central Sacramento Valley and northeast foothills.
Today is a great day to secure any loose outdoor items to prepare
for the potential of gutsy winds.

Precipitation should move through the area relatively quickly,
with most of the heavier rain/snow ending by Sunday morning. A
noticeable sensible weather impact from this system will be the
drop in high temperatures around the region. Saturday, we can
expect temperatures to be around 10-20 degrees cooler than today`s
high temps. Sunday we will start to slightly recover temperature
wise as the closed low moves further off to the east, with highs
in the mid 60s for the Valley and mid 30s to low 50s for higher
elevations. Monday, our high temperatures will climb back into
the low 70s for the Valley, with off-shore ridging beginning to
develop in the Pacific.

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...

Broad upper level troughing from the Pacific Northwest toward the
central Plains looks to remain in place through midweek. This will
induce continued northwesterly flow across interior NorCal during
the extended forecast period. A reinforcing shortwave looks to
travel through this flow pattern Tuesday into Wednesday, gradually
deepening the trough (and potentially retrograding it) through the
late week period. While precipitation impacts look to remain
displaced to the north and east of the region, this pattern looks
favorable for northerly surface winds to set up from Tuesday through
Friday of next week. Exact details such as timing and magnitude of
the winds is still somewhat uncertain, but ensemble guidance is
coming into agreement on a dry, warm, and windy pattern setting
up mid to late next week. Strongest winds, with gusts to 40 mph or
greater, are expected on Wednesday and Thursday, with still
breezy to locally gusty winds on Tuesday and Friday respectively.

&&

.AVIATION...

VFR conditions over interior NorCal until around 08z Saturday
then areas of MVFR/IFR becoming widespread as weather system moves
into the area. Local LIFR over mountains in precipitation. For the
Valley, surface winds at or below 12 knots until around 08z, then
southerly winds of 15-30 knots with local gusts 40 knots possible.
Over the mountains, southwesterly wind gusts of 40-50 knots
possible.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 11 AM Saturday to 8 AM PDT Sunday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

&&

$$