Area Forecast Discussion
Issued by NWS Sacramento, CA

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651
FXUS66 KSTO 071719
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
919 AM PST Wed Dec 7 2016

.SYNOPSIS...
A return to wetter weather will commence later today and continue
into next week.

&&

.DISCUSSION...
Valley temperatures have increased this morning. The Freeze
Warning has been allowed to expire as most locations are above
freezing now. Areas of fog are also dissipating with visibilities
and ceilings continue to improve as the morning progresses.

Current radar (around 9 am) showed precipitation off the northern
California coastline and is starting to move inland. Precipitation
should move over the Coastal Range and start impacting northern
interior California later today. Best estimate of precipitation
arrival for the valley into the Sierra is between 4 to 6 pm. JBB

Previous Discussion...A transition back to a more active weather
pattern (precipitation-wise) begins later today as a series of
more substantial systems begin to affect the region. Because of
the cold air already in place, expect snow levels to be rather low
when the first system arrives by this evening.

In Shasta County, snow levels could be in the 1000-1500 ft range,
and 2500-3000 ft along the Sierra foothills. Precipitation is
generally expected to be light in those locations. Depending on
location, this cold air will be slow to mix out Wednesday night
into Thursday, especially in the northern mountains. Strong warm-
advection may be more successful in bringing rising snow levels in
the northern Sierra by later Thursday.

Additional impulses arrive Thursday & Friday, possibly into
Saturday. This will come in the form of a narrow plume of
moisture, so some locations may miss out on precipitation with
those impulses. The Sierra will likely see heavier precipitation
with those waves with high snow levels.

&&

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)

An active, large scale pattern will continue through the extended
forecast with an abundant moisture tap. The mid to upper level
pattern is quite zonal, and it is difficult to determine any
definitive breaks in the steady moisture tap this far out.

Guidance suggests a brief lull in precipitation occurs Saturday
night into early Sunday before the next system moves in later in
the today and continues with the precipitation ebb and flow into
mid next week. There are differences in timing and evolution of
this system as the GFS is the fastest and more moist solution.
Regardless, widespread precipitation can be expected across the
forecast area. The longer Sunday to Wednesday period appears to
have a more plentiful moisture tap than the upcoming, shorter
Thursday to Saturday event, and you would expect increased
forecast accumulations. However, this is not the case because we
had to compromise due to the GFS vs ECMWF precipitation
differences. The GFS has been the wetter model the past couple
days, but the ECMWF has been consistently drier. Nevertheless, stay
tuned for updates, as forecast amounts for next week could
increase over time. Snow levels are around 3500 feet across
northern mountains and 4500 to 5500 feet in the Sierra on Sunday,
then increasing into Tuesday with the warm air advection.
JClapp

&&

.AVIATION...

Areas of Valley MVFR generally south of MYV due to BR/FG through
18z today. Light northerly flow under 10 kts thru the period.
Precipitation should approach the Coastal Range mainly after 20z
today and spread across NorCal this evening. JClapp


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
Thursday for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.

Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
Thursday for Shasta Lake Area / Northern Shasta County.

&&

$$



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