Weather Service Report


649 
FXUS66 KSTO 171247
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
447 AM PST Fri Nov 17 2017


.SYNOPSIS...
A few Sierra crest showers this morning...otherwise dry today and
Saturday with morning valley fog. Another weather system moves 
through Sunday night and Monday with another system coming through
mid week. Each of these next systems will come with light to 
moderate precipitation and high snow levels at generally above 
pass levels.

&&

.DISCUSSION...
Upper level trough axis has now moved inland with lingering
showers over the northern Sierra slowly ending. A shortwave trough
rotating around the base of the main low now over the northern
Sacramento valley is bringing a few light showers there but even
those are now moving into the Sierra foothills as the main low
shifts east. With minimal shower activity this morning, have
allowed the winter storm warning for the Sierra/Cascade crest to
expire. Clouds have begun to clear in some central valley
locations so could see some areas of morning fog. After mid day
today, skies should be mainly clear over the CWA. Cool airmass
will keep mountain temperatures the same or a little below
Thursday readings while more sun in the valley will allow for a
little warming in some areas there. Upper ridging pushes in over
the state tonight and Saturday bringing mainly fair skies. Main
forecast issue over the weekend will be morning valley fog which 
will be likely due to the fair skies, generally light winds under 
the ridge and abundant surface moisture. This time of year it is 
likely that some of this fog will become locally dense. Warming
airmass and clearing skies will allow for a little daytime warming
most areas with daytime highs pushing up close to normal for this
time of year. Norcal remains under the ridge on Sunday for another
dry day with valley fog during the late night and early morning
hours. 

Next Pacific storm on the horizon is forecast to move on to the
north coast Sunday night. Model timing has slowed a bit so have
made adjustments to precipitation onset time. By Monday morning,
entire forecast area will be under a threat of precipitation. Warm
advection will push up snow levels generally above pass levels by
Monday morning so mountain travel impacts with this system should
be fairly minimal. The main frontal band is forecast to push 
through the north state Monday afternoon. QPF with this system is 
not particularly impressive at this time as the main energy with 
this system is expected to move north of the forecast area as it 
rides over upper ridging over the southwest U.S. 
&&


.EXTENDED DISCUSSION (Tuesday THROUGH Friday)



Upper level ridge moves eastward as another disturbance slides
into northern California with more chances for precipitation.
Model forecasts are in general agreement to the atmospheric flow
pattern with moisture streaming into the coast in an atmospheric
river type pattern, but right now latest model runs have the brunt
of the precipitation remaining well to the north of California. If
this pattern holds true, light to moderate rain across the
forecast area can be expected with snow levels well above pass
level and light accumulations at high peaks.
&&

.AVIATION...



VFR/MVFR conditions with occasional IFR conditions in the valley
with fog and low stratus development towards the morning hours.
Fog and low clouds will diminish in the late morning to early
afternoon hours to mostly clear skies and VFR conditions for the
TAF sites.
&&

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

$$

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Western Regional Climate Center, wrcc@dri.edu