Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 160004
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
404 PM PST Sun Jan 15 2017

.Synopsis...
Fairly dry conditions through Tuesday. A series of winter storms
will begin Wednesday and continue into early next week. Use these
dry days to prepare now for another extended wet pattern with
renewed flooding and mountain snow concerns.

&&
.Discussion...
Skies may not clear in some spots over the Southern Sacramento
and Northern San Joaquin Valley...while other areas will continue
to slowly clear late in the afternoon and early evening. Fog will
set up again starting this evening. A similar cycle is expected
for tonight with the cleared areas starting to see some fog during
the evening hours showing improvement as ceilings form and along
the fringes of the low cloud area generally having the worst
visibility`s. The height of the ceilings will be lower tonight
closer to 1000 ft instead of the close to 2000 ft we had this
morning. We could see this pattern into Tuesday morning with
better clearing expected for the afternoon.

Wednesday is when the first of a series of winter type storms
moves into the region. The timing is still a little uncertain as
to when rain starts from either in the morning or afternoon hours
for many areas but seem consistent with starting the rain along
the coastal range and over the north end of the valley in the
morning. Models are not consistent on whether the precipitation
will start out as rain or snow near the major trans-Sierra passes
during the day but do agree that lower snow levels below the
passes will occur as the main part of the storm moves into the
region by late afternoon and lowering Wednesday night down to
around 3500 to 4500 feet...with the lower levels being over Shasta
County.

The system looks like a decent winter storm with the higher
totals focused over the north. (0.50) to (1.00) of rain is
expected in the central valley with up to (2.00) in the north.
(1.00) to (3.00) inches for the foothills and mountains with the
higher totals over Butte County and Western Shasta County. (8.0)
to (14.0) inches of snow can be expected near major pass levels
with (2.0) to (3.0) inches between 4000 and 5000 feet.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

Unsettled weather will continue through the extended as a series
of storms move across interior NorCal. Main change regarding this
forecast package was to lower QPF amounts over the Sierra with
the first system. This is due to moisture and main dynamics
tracking a little further south than originally expected. Some
lingering shower activity will continue over the area on
Thursday with snow levels around 3500-4000 feet.

Forecast models generally agree for the rest of the extended
period, as additional cold storms follow the mid-week upper
system. A second upper trough and associated frontal band will
approach the Coastal Range late Thursday evening, with widespread
precipitation following on Friday. Cold air associated with this
system may drop snow levels by Saturday morning to around 1500
feet for the northern mountains and 2500 feet over the Sierra,
with possible accumulating snow down into the Foothills. Gusty
winds are expected as the system moves through.

A third, stronger, and colder system is expected early next week.
Upper flow appears to be favorable for orographic precipitation
over the Sierra. Given the cold nature of these systems, hazardous
mountain travel could result over the weekend. Stay tuned for
details as model output could change this far out.


&&

.AVIATION...

Local MVFR ceilings from KAUN southward due to low stratus. Fog
and low ceilings redevelop by 04Z Monday. Otherwise, VFR
conditions for the higher foothills and mountains next 24 hours.
&&

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

$$



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