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Area forecast discussion 
National Weather Service Sacramento California
925 PM PST Mon Dec 5 2016

Synopsis...
cold overnight temperatures tonight and Tuesday night. A return
to wetter weather is expected Wednesday through Saturday.

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Discussion...
high clouds will continue to drift across the region at this time
but are slowly being pushed southward as the trough deepens. This
should help fog to form from around the central Sacramento Valley
southward later tonight and Tuesday morning. The weak system
moves through the northern part of the state on Tuesday. This
system will only produce light amounts of precipitation less than
a tenth of an inch in the mountains. The far north end of the
valley may see a few light showers but for the most part most
locations outside of the mountains north of US-50 will not see any
showers.

Temperatures tonight look like they will cool off into the mid 30s
by morning in the Central Valley with some of the coldest spots
dipping into the lower 30s. The coldest morning still looks to be
on Wednesday. At this time widespread morning lows around the
freezing mark with some of the colder spots dipping into the
upper 20s still looks possible. The durations at or below zero
should not exceed several hours for most locations. Mountain
Valley lows will get very cold dipping into the single digits and
teens. There looks like high clouds drifting over the region by
Wednesday morning should help to mitigate the low temperatures and
prevent them form dipping colder than freezing in many places.

The cold morning lows will be short lived as a stronger more
significant system moves into the region Wednesday night into
Thursday. Snow levels should be low to start Wednesday night but
rise on Thursday to near or just above pass levels by mid to late
morning. The focus of where the heavier rain will occur at least
into Friday varies depending on the model with the NAM showing the
several inches of rain by Friday morning north of I-80 and a
couple of inches to the south for the western slopes. The valley
could see one half to an inch of rain during this time period.

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Extended discussion (friday through monday)

Unsettled pattern looks to continue thru much of the extended
period. Precipitation will continue during the day Friday as swath
of moisture continues to steam in. Current model solutions suggest
moisture plume will intrude into the Bay area and up into the
Sierra across southern portions of the forecast area (perhaps Hwy
50 corridor and south). This would keep snow level near 7000 feet
over the Sierra during the day. Regardless, some decent
accumulations possible which may serve to impact travel heading
over the passes. Northwest portions may see a bit of a break in
precipitation during the period on back side of wave. Model
solutions diverge from Friday night with the European model (ecmwf) showing an
additional wave of precipitation, perhaps substantial, during the
day Saturday, while GFS remains mostly dry outside a few Sierra
showers. Given such a large difference, have hedged toward a blend
of solutions with precipitation over most of the area, until
solutions are better aligned. Snow levels may drop lower with this
wave should it occur which would further impact weekend mountain
travel. Certainly something to keep an eye on going forward.

Next wave moves across the area on Sunday. GFS wetter with this
wave vs drier European model (ecmwf). Regardless, looks like best chance for
widespread precip across the mountains with spottier showers at
lower elevations. Snow levels around 4000 feet across northern
mountains and 5000 feet in the Sierra. Showers taper off later
Sunday into Monday, with a break in precipitation possibly. Models
hint at additional systems into middle of next week!

Ceo



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Aviation...

Areas of valley MVFR and local IFR to LIFR in br/fog possible
again Tuesday morning generally south of myv. Light northerly flow
under 10 kts thru the period.



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Sto watches/warnings/advisories...
freeze watch from late Tuesday night through Wednesday morning
for central Sacramento Valley-Clear Lake/Southern Lake County-
motherlode-northeast foothills/Sacramento Valley-northern
Sacramento Valley-northern San Joaquin Valley-southern
Sacramento Valley.

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