099
FXUS66 KSTO 040930
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
230 AM PDT Sat May 4 2024

.SYNOPSIS...
A weather system moves through the area today bringing showers,
mountain snow, isolated thunderstorms, gusty winds and cooler
temperatures. Warmer and drier conditions return next week with
gusty north to east winds mid-week.

&&

Current radar shows the weather system starting to move into far
northwestern California this morning. Precipitation will spread
inland through the day today, in the form of Valley and foothill
showers, and mountain snow. Latest guidance from WPC shows storm
total QPF of around 0.50"-1.25" in the Valley, with 1"-3" in the
foothills and mountains. Isolated thunderstorms are also in the
forecast for today (15-30% probability). Brief heavy rain, small
hail, lightning, gusty winds and brief funnel clouds will be
possible with any thunderstorms that develop. Best chances are
north of Interstate 80.

For the mountains, snow is expected today, heavy at times. Storm
total snow amounts have increased slightly. The National Blend of
Models (NBM) advertises a 75-95% probability of 8 inches of snow
or more, and 50-90% probability of 12 inches or more. Snow levels
have also trended slightly lower, and the Winter Storm Warning
area has been expanded to include elevations above 4000 feet. Snow
levels will initially be around 4000-5000 feet this afternoon and
lower to around 2500-3500 feet by early Sunday morning. Snow
rates of 1-2 inches per hour, combined with gusty winds will lead
to travel delays, reduced visibilities, snow covered roads and
chain controls. People should check the forecast and road
conditions before traveling in the mountains this weekend.

Gusty south to southwest winds are also developing ahead of the
storm. A Wind Advisory has been issued for portions of the
Northern and Central Sacramento Valley, mainly east of Interstate
5, and the Northeast Foothills through 11 AM this morning. The NBM
shows a 65-95% probability of 40 mph gusts or greater in this
area, and a 55-95% probability of 50 mph gusts in the mountains
where the Winter Storm Warning is in place. Much cooler
temperatures will also influence the area, with highs around 15 to
20 degrees below the climatological normal for this time of year
today, which is also highlighted with a strong signature on the
Extreme Forecast Index (EFI). Precipitation tapers off on Sunday,
as just a few showers and mountain snow showers linger in the
mountains. Temperatures will gradually warm next week, with
periods of breezy winds.

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Ensemble guidance and cluster analysis indicate a dry, warm and
windy pattern setting up for mid to late next week. There is still
some uncertainty with the exact details such as timing and
magnitude of the winds. The Extreme Forecast Index (EFI) is
highlighting strong north to east winds in the typical wind prone
areas for this direction which would include the western portion
of the Valley and in the mountains. The National Blend of Models
(NBM) shows a 55 to 85 percent probability of wind gusts greater
than 40 mph in those areas on Wednesday. Temperatures gradually
warm over the extended forecast period, returning to the 80s in
the Valley.

&&

.AVIATION...
Pacific weather system moves through today with widespread MVFR
conditions spreading south in the Central Valley through the
morning, then generally VFR after 21Z except MVFR vicinity
scattered showers and isolated thunderstorms. In the Sierra,
widespread IFR/LIFR conditions develop after 15Z with rain, snow
and thunderstorms. Snow levels lowering to 5000-6000 feet this
afternoon, and to around 3500 feet tonight. Widespread southerly
surface wind gusts 25-35 kts with 35-45 kts over higher terrain.
Wind decreasing in the Central Valley after 00Z Sunday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 11 AM PDT this morning for Central
Sacramento Valley-Northeast Foothills/Sacramento Valley-Northern
Sacramento Valley.

Winter Storm Warning from 11 AM this morning to 8 AM PDT Sunday
for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$