075
FXUS66 KSTO 012059
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
159 PM PDT Wed May 1 2024


.Synopsis...
Gusty north winds weaken this evening. Dry and mild weather with
breezy winds through Friday. Precipitation chances return this
weekend.

&&

We had a blustery start to the month of May today throughout the
Valley as winds reached 30-35 mph in several places in the Sac
Valley along the I-5 corridor. The Wind Advisory has been
cancelled, but northerly winds will remain breezy as they
gradually weekend this evening. Widespread gusty north winds
return on Thursday, but remain below advisory criteria. Gusts are
forecast to be between 20-30 mph. Otherwise, dry and mild weather
will continue through the remainder of the work week with highs
in the Central Valley in the upper 70s to mid 80s. The warmest day
of the week will be on Friday with highs in the low to mid 80s.
Valley high temperatures plummet into the 60s as a storm system
moves into the area on Saturday.

Confidence is increasing that we`ll see a rapid change back to
cool and unsettled weather this weekend as a strong trough digs
south into NorCal from the Gulf of Alaska bringing widespread
precipitation, high elevation snow, and isolated thunderstorms
over the weekend.


&&


.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...
Ensemble guidance is beginning to come into agreement on the
general synoptic evolution of a trough digging toward interior
NorCal from the Pacific Northwest over the weekend. This pattern
shift will result in the return of active weather, with rain
showers, isolated thunderstorms, high elevation mountain snow, and
gusty winds all possible on Saturday, with some precipitation
impacts then lingering on Sunday as well. Strongest southwesterly
winds are expected over the Sierra, where gusts of 40 to 50 mph
will be possible, with 20 to 35 mph gusts possible elsewhere.
Additionally, a notable cool down is anticipated over the weekend
as this system travels through the region. Valley high
temperatures in the low to mid 80s on Friday afternoon look to
fall into the low to mid 60s for Saturday.

While the general synoptic evolution largely remains on track, there
are some subtle differences in the exact track and strength of the
trough that are leading to some uncertainty in precipitation totals
at this time. Regardless, heaviest precipitation is expected to
occur over the Sierra and adjacent foothills, with lesser, but still
appreciable precipitation accumulations in the Valley. Current
probabilities of liquid precipitation exceeding 0.5" through Sunday
are in the 15% to 35% range through much of the Valley and in the
50% to 70% range for the Sierra, foothills, and northern Sacramento
Valley. Notably, probabilities of liquid precipitation exceeding
1.00" are still in the 30% to 60% range for the Sierra, foothills,
and northern Sacramento Valley as well. There is also a 15% to 25%
chance for isolated thunderstorm development Saturday afternoon and
evening, which could yield locally higher rainfall totals.

Attendant snowfall remains somewhat uncertain as well due to a
variety of factors. While the exact track of the trough will have a
bearing on the overall precipitation amounts, it will also play a
role in the timing and magnitude of dropping snow levels as well.
Currently, snow levels look to remain high, around 5500` to 7500` on
Saturday, then rapidly dropping late Saturday afternoon through
Sunday morning to around 3500` to 4500`. Heaviest precipitation (and
resultant snowfall) is currently expected to occur Saturday
afternoon and evening, with the falling snow levels lagging somewhat
behind this period. As a result, the bulk of accumulating snowfall
is expected to occur above 5000`, although some light accumulations
will still be possible down to 4500`. Total snowfall accumulations
may be impacted some initially by antecedent warm temperatures from
the last few weeks as well. That being said, current probabilities
of exceeding 4" of snowfall along the Sierra are in the 50% to 70%
range above 5000`, with 30% to 50% probabilities of exceeding 8" of
snow above 6000`.

This trough looks to remain rather progressive as it expected to be
centered more over the Great Basin by Sunday afternoon/evening. As a
result, some precipitation may linger over the Sierra and adjacent
foothills locations through Sunday morning, but is expected to taper
off through the remainder of the day. The unseasonably cool
temperatures will look to stick around, with Valley high
temperatures in the mid 60s and higher elevations in the 40s to 50s
on Sunday afternoon. Long range ensemble guidance then keeps
interior NorCal underneath broad northwesterly flow aloft through
early to mid next week. This will result in a gradual warming trend,
with a return to near normal temperatures by Wednesday. Given the
flow pattern, some unsettled weather may remain possible next week,
but there are currently no distinct signals for impactful weather at
this time.


&&


.AVIATION...
VFR conditions over interior NorCal into Thursday. For Central
Valley, northerly surface winds around 15-25 knots, with gusts up
to 35 knots possible until around 02z. Winds decreasing to around
12 knots thereafter until around 15z with northerly winds
increasing to 15-25 knots. In foothills and mountains, north to
east surface wind gusts of around 15-30 knots.

&&

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

&&

$$