798
FXUS66 KSTO 090945
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
145 AM PST Sat Nov 9 2024

.SYNOPSIS...
Seasonable temperatures and mainly dry weather through Sunday. An
unsettled weather pattern is forecasted to start on Monday
bringing widespread rain, high-elevation snow, and chances for
thunderstorms. Unsettled weather is expected to continue next
week.

.DISCUSSION...
This weekend sees mostly dry, quiet weather, with seasonable
temperatures, but with partly cloudy to overcast skies. There`s an
outside chance for a few sprinkles overnight on Saturday and into
Sunday in the northern parts of the Sacramento Valley, though
little to no accumulations are expected from this.

Overnight Sunday and into Monday, a fast moving upper level
trough progresses into the area, bringing widespread chances for
precipitation, mountain snow, gusty onshore winds, and a slight
chance for Valley thunderstorms. Overall precipitation amounts
appear to remain similar to the last 24 hours, with NBM predicting
a 60 to 90% chance of 0.5 inches or more north of I-80 (30 to 60%
further south), and 50 to 80% probability of one inch or more in
the foothills and mountains. The majority of snow appears to
remain at higher elevations in the mountains, with NBM
probabilities of 60 to 80% for 2 inches or more above 6000 ft (30
to 60% probability for 4 inches or more at the same elevations).
Winds will be strongest in the Delta and over the mountains, with
southerly gusts in the Delta and Valley around 20 to 30 mph, and
more southwesterly gusts around 25 to 40 mph over the Sierra.
Finally, there is a 10 to 15% probability of isolated Valley
thunderstorms on Monday; these probabilities have trended down
since the afternoon forecast, though how chances evolve moving
forward will likely be dependent on the progression of the storm
system and how cloud cover interacts with any surface instability.

By Tuesday the aforementioned system exits interior NorCal,
leaving us with some lingering mountain rain and snow showers,
but primarily dry and cool conditions everywhere else. The exiting
trough leaves us with cooler than normal daytime highs, before a
new weather system arrives mid to late week.

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
While there is still uncertainty with regards to the intensity of
the mid to late week system, cluster analysis and ensembles have
come into much better agreement over the last 24 hours on the path
and general timing of the trough. Currently, ensembles seem to
agree on the upper level low digging down along the coast of
California on Thursday, before moving more inland on Friday and
into Saturday. There is more uncertainty at this point, whether
the system will be prolonged by a secondary low progressing
southward and joining the first, or if those will primarily be
distinct systems.

For the remainder of the current forecast period, the NBM is
showing the majority of precipitation occurring on Friday, with
an 30 to 60% probability of 0.5 inches or more across the area
between Friday morning and Saturday morning. Over the course of 72
hours between Thursday and Saturday morning, current NBM
predictions show a 45 to 80% probability of an inch or more north
of I-80, and 20 to 50% chance south of the interstate. Snow levels
will remain mostly above 6000 feet (though they will lower to
closer to 5000 feet towards the tail end of the system on
Saturday). Still, at elevations above 6000 ft, the NBM has a 50 to
70% chance of 4 inches or more on Friday alone. Over a 72 hour
period from Thursday to Saturday morning, there is a 40 to 65%
probability of 8 inches or more in the Sierra and southern
Cascades.

&&

.AVIATION...
VFR conditions prevail across interior Northern California over
the next 24 hours, with surface winds below 12 kts. Increasing mid
to high level clouds today with areas of BKN to OVC skies at
around 15 to 25 kft.

&&

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

&&

$$