FXUS66 KSTO 132231
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
231 PM PST Fri Dec 13 2019
SYNOPSIS...
Light valley rain and moderate mountain snow through Saturday
night, Mountain travel delays are likely. Drier weather Sunday and
early next week.
.DISCUSSION
...
A relatively warm and moist system will continue passing through
northern California into Saturday. Main precipitation band will
move through late this afternoon/early evening. Snow levels are
fairly high currently above 6500 feet, but will gradually lower
to near 4000 feet by Saturday night. Valley rainfall amounts will
be light generally under 0.25 inches, except 0.50-1.00 inches
northern Sacramento Valley(Redding area), a bit more impressive
amounts over the mountains and foothills from 1-2 inches of
liquid. Snow amounts of 10 to 15 inches, locally 2 feet will be
possible above 6500 feet, especially near pass level. A brief
break in the showers will be possible Saturday afternoon, a second
colder, but drier system will drop through Saturday night. Not
much moisture with this system and conditions will remain dry for
the Valley, 2 to 4 inches of additional snow will be possible
above 4000 feet. Dry weather returns Sunday into early next week,
as high pressure ridging builds over NorCal.
.EXTENDED DISCUSSION
(Tuesday THROUGH Friday)...
The brief dry trend from the weekend will continue into early next
week. On Tuesday, the transitory ridge to likely shift over toward
the Central Great Basin ahead of a compact upper low nearing the
California coast. Given the complex of nature of this system
separating from the westerlies and eventually closing off,
uncertainty still plagues the forecast. While the GFS/ECMWF
ensembles agree on the existence of this system, they continue to
exhibit spatio-temporal differences. The former model suite
remains the wetter solution with widespread precipitation entering
the picture by mid-week. On the contrary, The ECMWF ensemble
system takes a more southern track favoring impacts down in
southern California. There is enough ensemble spread to keep
either scenario in play so will continue maintaining precipitation
in the forecast. Expect increasing cloud cover given the influx of
Pacific moisture with near average temperatures for mid-December.
Looking toward the following weekend, there are still fairly
strong signals of wet weather in response to a full-latitude
trough approaching the Pacific coast. While some of the 24-hour
probabilities for 0.50 and 1.00 inches of precipitation have come
down a bit, this will continue to be watched. The Climate
Prediction Center experimental Day 8-14 hazards supports this
notion with Dec 20-22 being highlighted for heavy precipitation
which includes snow in the mountains. ~BRO
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