Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 171213
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
413 AM PST Wed Dec 17 2014

.Synopsis...
Showers today with a brief break in precipitation some areas on
Thursday. Next frontal passage on Friday with light to moderate
rain and higher elevation snow. Mountain showers possible over the
weekend but mainly dry in the valley. Dry all areas Monday through
mid week under west coast high pressure ridge.

&&

.Discussion...
Weakening frontal band moving into the Sierra as this time
bringing scattered light showers with snow above about 5000 feet.
These showers will be winding down later this morning as this
system shifts to the east. At this time...chain controls still
exist over the major Sierra passes so will leave up current snow
advisory until the early morning showers dissipate more. Another
secondary trough now crossing about 130 west will be dropping
through NORCAL late this afternoon or evening bringing another
round of relatively light precipitation. A shortwave ridge has
been consistently forecast to slide over the west coast on
Thursday bringing a period of drying most areas. Models now
indicating that this will be a somewhat dirty ridge allowing a
threat of some light precipitation to fall over the coast range
and northern mountains. Models in good agreement in displacing the
ridge eastward on Friday as the next Pacific frontal system moves
across the west coast. Models not as consistent with precipitation
amounts. GFS is the driest with this system bringing light rain
with a few inches of snow to the mountains. The wettest (GEM)
model would bring moderate rain with several inches of snowfall to
the mountains. Have kept forecast amounts leaned towards the light
side at this time as this system will be pushing into a ridge and
have kept QPF fairly low impact. Upper ridging begins to rebuild
on Saturday with more amplification on Sunday. As a
result...should see a shift in the precipitation threat to the
north with Sunday expected to remain dry all areas with the
exception of the far northern mountains over Shasta county,


.Extended Discussion (Sunday through Wednesday)

Medium range models similar in transitioning to a drier weather
pattern over the weekend into early next week. Some light precip
continues to be depicted over the Shasta mountains Sunday,
otherwise dry weather with the main weather concern being impact
of valley stratus and/or fog nights and mornings. Models
strengthen upper high in EPAC with associated upper ridge building
over Interior NorCal.

Models waver on a trough weakening the west coast ridge Tuesday.
A trough tries to slide downstream of the ridge axis from the Pac
NW into the western Great Basin. With the uncertainty, we have
introduced a slight chance of precip over mountains
Tuesday.      JClapp

&&

.Aviation...

Expect lingering bands of showers today. Mainly VFR cig in valley
with isold MVFR cig. Mtns obscured much of day northward of hwy 50.
Snow levels approx 035 MSL in Shasta mtns and approx 045 MSL near
I-80/HWY 50.    JClapp

&&

.STO Watches/Warnings/Advisories...
winter weather advisory until noon pst today above 4000 feet in
the west slope northern sierra nevada...western plumas
county/lassen park.

&&

$$







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