FXUS66 KSTO 132227
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
227 PM PST Wed Nov 13 2024
SYNOPSIS...
Periods of scattered light to moderate snow, rain, and breezy
winds expected today through Friday with moderate mountain travel
impacts. Northern CA remains in an active weather pattern at the
end of this week into early next week.
.DISCUSSION
...
Scattered showers are slowly trekking across interior Northern
California this afternoon, as a low pressure system brings low to
moderate impacts to the area. Locations in the northern
Sacramento Valley and adjacent foothills have observed rainfall
amounts ranging from 0.04" to 0.15" [as of 12 pm PST] with higher
totals 0.25" to 0.50" in far north Shasta County. Southerly winds
are also quite gusty this afternoon with gusts 20 to 36 mph being
observed across portions of the Sacramento Valley. Scattered
showers will continue to move across the region throughout the
day which will result in slick roads and intermittently rainy
conditions during rush hour. Additionally, the National Blend of
Models (NBM) is indicating a 10-15% chance of thunderstorms this
afternoon and evening over Shasta County. Winds will continue to
gust 20 to 35 mph in the Valley/foothills and up to 45 mph over
the mountains through the evening before dying down early tomorrow
morning.
By Thursday morning, scattered snow showers are expected to
linger over the Sierra, while Valley and foothill locations
experience a couple hours of drier weather with a few isolated
showers scattered about. The next round of scattered showers is
expected to move through midday Thursday into Friday, which will
bring additional rain and snowfall accumulations, as well as a 15-20%
chance of isolated thunderstorms north of I-80. At present,
debris flow concerns are low around the Park Fire Burn Scar but
conditions will continue to be closely monitored throughout this
event. Rain probabilities of an inch or greater for the mountains
and Northern Sacramento Valley are 65-95% chance where the
majority of precipitation is expected. Over the Northern San
Joaquin Valley and Southern Sacramento Valley, probabilities for a
half inch or greater are 30-50%.
Periods of light to moderate mountain snow will also accompany
this weather system, beginning early this afternoon through Friday
night. Snow levels are between 5500-6500 feet, dropping to
4500-5500 feet Thursday night, and 4000-5000 feet Friday morning.
A Winter Weather Advisory has been issued for the Western Slope
Northern Sierra/Western Plumas/Lassen Park Counties above 5500
feet for snow accumulations of 6 to 12 inches and gusts up to 45
MPH through 10 PM Friday. Snow will be heaviest this afternoon and
evening with another round of scattered snow showers Thursday
night into Friday morning. NBM probabilities for amounts greater
than 12 inches is 60-80% between today and Friday night, peaking
south of Interstate 80. The peaks of Lassen Nation Park area may
see to 2-3 feet of snow, with 12-18 inches across the higher peak
of the Sierra. Conditions begin to taper off on Friday outside of
lingering snow showers across the Sierra through the evening
hours.
Following this system, minimum temperatures will be near freezing
Saturday and Sunday mornings across portions of the Valley which
may lead to patchy frost. Probabilities for minimum temperatures
less than 35 deg F are 25-45% on Saturday and 15 to 35% on Sunday.
Lows in the mountains and foothills will be in the teens to low
30s, with areas of frost. Northern CA will remain in a wet and
active pattern heading into early next week, as another weather
system brings renewed chances for rain and mountain snow.
.EXTENDED DISCUSSION
(Sunday THROUGH Wednesday)...
Ensemble guidance and cluster analysis indicate upper level
ridging creeping in on Sunday, followed by a shortwave trough
moving through later Sunday into Monday, bringing showers, and
mountain snow showers to the forecast area. The National Blend of
Models (NBM) projects a 45-85% probability of rain amounts of
0.25" or greater in the mountains and upper foothills, with 20-50%
in the Valley and lower foothills. There is also a 20-50%
probability of snow amounts of 4 inches or greater in the Sierra
Nevada above 6000 feet. Snow levels initially start off around
5500-6500 feet Sunday afternoon, and lower to around 4000 feet
Monday morning. Drier weather is expected Monday night into
midweek with some gusty north to east winds as upper level ridging
builds back into the area. Chilly mornings are also in the
forecast over the weekend and into early next week. Temperatures
gradually trend higher next week, with daytime highs becoming near
normal by Wednesday.
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