155
FXUS66 KSTO 092227
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
227 PM PST Sat Nov 9 2024


.SYNOPSIS...
There is a quick moving system on Monday which is expected to
bring mountain snow, rain, and chances for thunderstorms to
interior Northern California. A potentially much stronger second
system is expected mid to late week, bringing rain and mountain
snow through the end of the week.

.DISCUSSION...
This weekend will continue mostly dry, quiet weather, with
seasonable temperatures, but with partly cloudy to overcast skies.
There`s a slight chance for a few sprinkles tonight over the northern
Coastal Range and the mountains of Shasta County, but little to
no measurable rainfall is expected.

Overnight Sunday and into Monday, a fast moving upper level
trough with a cold front progresses through the area, bringing
widespread chances for precipitation, mountain snow, gusty onshore
winds, and a slight chance for isolated thunderstorms over the
northern and central Sacramento Valley and northeast foothills.
Being a quick hitting system will limit storm total precipitation
amounts to some extent. The latest NBM has increased
precipitation amounts south of I-80, predicting a 60 to 90% chance
of 1.0 inches or more in the mountains and foothills, lowest
south of Highway 4. The Valley has a 45% to 95% of 0.5" or more,
lowest over the northern San Joaquin Valley, highest over the
northern Sacramento Valley.

The majority of snow appears to be above 6000 ft, where there is a
60 to 90% probability for 4 inches or more. Currently amounts up
to 8" are possible at pass levels. This could cause significant
travel difficulties, especially being an early season event and at
the end of a holiday weekend. Due to potential winter driving
impacts, a Winter Weather Advisory has been issued for 10 AM
Monday to midnight Monday night (12 AM Tuesday). Along with snow,
gusty southwest winds are expected, gusting up to 45 mph. Heavier
snow should taper off fairly quickly, with just a few lingering
snow showers by early Tuesday.

Winds will also be gusty in the Delta and Sacramento Valley,
gusting up to around 20 to 30 mph during the day Monday. Finally,
there is a 10 to 15% probability of isolated northern/central
Sacramento Valley and northeast foothills thunderstorms on Monday
afternoon and early evening. Most of these storms will develop
with the cold front. Cloud cover could limit instability.

As the system exits interior NorCal on Tuesday, a bit of a lull
 in precipitation is expected. The exiting trough leaves us with
cooler than normal daytime highs. Another potentially stronger,
wetter system arrives mid to late week.

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Another system approaches the area Wednesday and will bring
chances for widespread wetting rain and high-elevation mountain
snow through the weekend. Cluster analysis and ensembles continue
to come into better agreement, depicting an upper level low
digging down along the coast of California on Thursday, before
digging further south and moving inland on Friday and into
Saturday when the heaviest, most widespread precipitation is
expected.

For this multi-day system, the NBM shows a 45 to 80% probability
of an inch or more of rainfall north of I-80, and 20 to 40%
chance south of the interstate. Probabilities of seeing over an
inch of rain in the mountains and foothills is roughly 70 to 90%.
In terms of snowfall, there is a 60 to 80% probability of 8
inches or more in the Sierra and southern Cascades. The most
widespread heavy winter precipitation is expected Friday into
Saturday, when the NBM has a 70 to 80% chance of 4 inches or more
on Friday alone. Snow levels will remain mostly above 6000 feet,
before lowering to around 4500-5500 feet Friday night into
Saturday. Additionally with this system, southerly winds are
expected to periodically gust 15 to 30 mph in the Valley with
gusts up to 40 mph over the Sierra, especially Wednesday evening.

There is the potential for a period of lighter, lower impact
precipitation on Thursday, before the heavier precipitation moves
in on Friday, but this is where the majority of the uncertainty
lies. Regardless, active weather is expected for the later half of
this upcoming week so be sure to check the forecast before
heading out the door.

&&

.AVIATION...
VFR conditions with surface winds below 12 knots prevail across
interior Northern California over the next 24 hours. &&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 AM Monday to midnight PST Monday
night for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

&&

$$