Scientific Forecaster Discussion
fxus66 ksto 141101
Area forecast discussion
National Weather Service Sacramento California
301 am PST Sat Dec 14 2019
light valley rain and moderate mountain snow through late
tonight. Mountain travel delays are likely. Drier weather returns
Sunday and early next week. Unsettled conditions are possible
beginning the middle of next week.
spatial coverage of mountain snow showers continue to be on the
decrease per radar trends from kbbx and kdax. The weak mid-level
speed maxima that initiated the evening showers has exited the
region with quasi-zonal flow remaining in the wake. Most locations
will remain mostly cloudy with a few pockets of fog where winds
become calm. More specifically, Redding continues to see patchy
fog with visibilities oscillating between 0.50 and 1.00 miles.
Additionally, some foothill locations stretching from Auburn down
through Jackson into Sonora can expect reduced visibilities at
times. However, not expecting a more widespread fog event given
the presence of abundant cloud cover.
Another band of precipitation is forecast to impact the Sierra by
as early as the late morning. This is in response to an offshore
trough which will quickly sweep through. General northwesterly
flow aloft should generally keep the valley on the drier side
although a few scattered showers cannot be ruled out. Another bout
of snow showers will impact the Sierra and southern Cascades
through much of the evening. With 700-mb temperatures dropping to
near -12c, snow levels will come down quite a bit. Current
forecast models show accumulations down to 4,000 feet, perhaps
slightly lower in some areas. A Winter Weather Advisory remains in
effect until 4 am Sunday with likely travel delays and chain
controls for mountain travelers. Another 3 to 6 inches of snow is
possible, with higher amounts in locally heavy showers.
As the system departs toward The Four Corners region, a building
ridge of high pressure over the Pacific will bring fair weather to
the region Sunday into early next week. Expect high temperatures
to stay close to climatology over the valley with 4 to 8 degree
departures more likely across the mountains. Through early
Tuesday, mornings will be cooler than recent days given more
optimal radiational cooling effects. Forecast lows over the
valley, Delta, and foothills will be in the 30s with teens and 20s
up in the mountains. Eventually an approaching trough should lead
to an increase in clouds on Tuesday which will moderate overnight
lows while precipitation may arrive by mid-week. ~Bro
Extended discussion (wednesday through saturday)...
the trend in the models handling of the mid-week system is more
progressive with the compact upper low moving inland on Wednesday.
Given the complex of nature of this system separating from the
westerlies, uncertainty still plagues the forecast.
Looking toward next weekend, there are still fairly strong
signals of wet weather, especially across the northern half of
the forecast area, in response to a full-latitude trough
approaching the Pacific coast.
areas of MVFR with local IFR/LIFR conditions next 24 hours,
except widespread IFR over higher terrain. Lingering showers
continue over the mountains with shower chances returning to the
valley after 03z Sunday. Snow levels 3500-4500 ft. Surface winds
generally less than 12 kts at taf sites. &&
Winter Weather Advisory until 4 am PST Sunday for West Slope