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fxus66 ksto 111137 
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Area forecast discussion
National Weather Service Sacramento California
337 am PST Wed Dec 11 2019



Synopsis...
light showers possible on Wednesday and Thursday. Widespread
precipitation expected later in the week and into the weekend.
Drier weather Sunday and early next week.

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Discussion...
a weak weather system moved through norcal last night spreading
precipitation across the area. The upper level trough has moved east
into Nevada with only lingering showers remaining early this
morning. Areas of light fog have developed behind the frontal
passage. Fog could become denser in areas this morning, though it
will be dependent on high cloud cover.

Upper level flow expected to become more zonal over norcal today. A
shortwave along a deep trough centered around the Gulf of Alaska
pushes into the West Coast today, bringing an increased chance of
light precipitation to areas generally north of I-80 this afternoon.
Increased precipitation is expected across most of the area
overnight Wednesday into Thursday, tapering off significantly south
of the Sacramento area. Heaviest precip amounts forecast in northern
Shasta County and mountains north of I-80 with amounts up to 0.75 to
1 inch possible. Lighter amounts expected in the rest of the valley
with only a few hundredths south of Sacramento up to around a
quarter of an inch in the northern Sacramento Valley. Snow levels
will mainly be above 7000 to 8000 feet with minimal accumulation
expected.

Ensembles continue to suggest precipitation chances continue Friday
through Saturday as impulses move along the zonal flow. The majority
of precipitation will remain in the foothills and mountains with
precipitation amounts of half an inch to an inch and a quarter
forecast. The valley could see anywhere from a few hundredths of
an inch to a quarter of an inch. Snow levels will begin to drop
Friday to around 6000 to 7000 feet before dropping below pass
level overnight Friday with light accumulation down to 4000 to
4500 feet possible. Snow accumulation around 5 to 10 inches is
possible over the Sierra which could cause hazardous travel
conditions over the Sierra passes. Hec

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Extended discussion (sunday through wednesday)...
to conclude the weekend, broad troughing will have shifted into
The Four Corners which allows for heights to build over the region
from Sunday into early next week. This supports a period of dry
weather accompanied by mostly sunny skies and near average
temperatures. From Tuesday Onward, there is a greater amount of
uncertainty in the offshore (upstream) pattern. Progressive flow
will carry a longwave trough across the central Pacific this
weekend with its fate dictating impacts over northern California.
While 06z gefs/00z European model (ecmwf) ensemble means show a trough entering the
picture next Tuesday/Wednesday (december 17/18), deterministic
guidance show the potential for a closed low to separate itself
from the prevailing westerlies. Such solutions are wildly variable
so confidence is low in the eventual outcome. However, did raise
the chances for precipitation in the forecast due to the presence
of the trough. ~Bro

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Aviation...
widespread MVFR/IFR conditions at taf sites through 20z. -Shra
possible across Central Valley through 16z. Precipitation returns
this afternoon with -ra possible after 23z. Light winds generally
less than 10 kts expected.

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Sto watches/warnings/advisories...
none.

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