Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 070042
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
442 PM PST Tue Dec 6 2016

.SYNOPSIS...
Cold overnight temperatures again tonight. A return to wetter
weather is expected Wednesday through Saturday, and again next
week.

&&

.DISCUSSION...
Northwesterly flow continues over Northern California. A weak
weather system is brushing by the region today, bringing isolated
snow showers mainly to the northern mountains and far northern
Sierra. Little to no accumulation is expected with these showers.

This system will additionally reinforce the cold airmass,
bringing perhaps the coldest temperatures of this extended cold
stretch tonight. Widespread subfreezing temperatures are forecast
across the Valley by early morning Wednesday.

A series of more substantial systems arrives starting Wednesday
afternoon/evening. Because of the cold air already in place,
expect snow levels to be rather low when the first system arrives.
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...but snow levels will rapidly rise to 7000+ feet
when they do.

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 heavy precipitation
with those waves with high snow levels.

Dang

&&
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)

Active large scale pattern will continue through the extended
forecast. Forecast models disagree on Saturday regarding shower
activity as upper energy pushes eastward. Precipitation amounts
and coverage and amounts differ this far out, with the GFS being
the driest solution. Have blended the solutions given model
uncertainty. Snow levels will be generally above 5000 feet on
Saturday over the northern Sierra, which could result in some
hazardous mountain travel.

Guidance suggests there could be a brief lull in shower
activity Saturday night into early Sunday before the next system
moves in early next week. There are differences in timing and
evolution of this system as the GFS is the fastest solution.
Regardless, widespread precipitation can be expected across the
forecast area. Snow levels around 3500 feet across northern
mountains and 4500 to 5500 feet in the Sierra on Monday, then
increasing into Tuesday with the warm air advection. Additional
waves of precipitation will continue at least through the middle
of next week so stay tuned for updates.

&&

.AVIATION...

Areas of Valley MVFR and local IFR to LIFR generally south of MYV
due to BR/FG through 18z Wednesday. Light northerly flow under 10
kts thru the period. Precipitation should approach the Coastal
Range mainly after 20z Wednesday as a storm system approaches.


&&

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

Freeze Warning from midnight tonight to 9 AM PST Wednesday for
Carquinez Strait and Delta-Central Sacramento Valley-Clear
Lake/Southern Lake County-Motherlode-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Southern Sacramento Valley.

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

&&

$$


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