Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 201857
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
1057 AM PST Thu Nov 20 2014

.Synopsis...
Two more weather systems continue to move through NorCal into
Saturday bringing periods of precipitation. The second system is
expected to be the wettest Friday night into Saturday. High
pressure builds over the area next week for generally dry weather
and milder daytime temperatures along with areas of morning valley
fog.

&&

.Discussion... Rain band progressing east through NorCal late
this morning. The system shows good satellite representation with
even a few lightning strikes off the coast...believe models may be
under doing QPF`s and precip chances. Have updated forecast to
increase precip chances and refine timing. Snow levels are
currently above 6000 feet and expect them to fall to 5000 feet
during the evening hours. 1 to 2 inches of snow is expected at
pass level and highways over the Sierra will likely become icy
after sunset...up to 4 inches could fall over the highest peaks.
Rainfall amounts for the valleys should be in the 0.25-0.50 range.

.Previous Discussion (Today through Sunday)...
The second of three relatively weak systems will move through the
region today into this evening with the greatest amounts
occurring later this afternoon through the evening commute.
Precip amounts with this system will be light once again with
valley locations remaining less than 0.20 and the mountains around
0.50 inches of liquid precip. Snow levels look lower with this
system at about 5500 feet, but most snow will likely be above 6000
feet. Even so, we only expect up to 2 inches of snow below major
pass levels in the Sierra. Lassen Peak is expected to have the
most at 5 to 6 inches.

Much of the day Friday will likely be dry, but cloudy in between
systems. The third system in this series of storms will move into
the region late on Friday/Friday evening through Saturday. This
system looks to be juicier than the previous two with breezy
conditions in the valley and windy conditions over the Sierra
crest. The west to east aligned jetstream core will be near the
CA/OR border, translating into higher snow levels since we would
be on the south side of the jet in the warmer airmass. The NAEFS
(North American Ensemble Forecast System) model is forecasting
percipitable water of 1.00 to 1.25 inches moving into northern to
central CA Friday night into Saturday. With the jetstream aligned
more west to east (good orographic lift) and the good moisture
fetch, the Shasta mountains and the Sierra are expected to receive
an additional 0.75 to 1.50 inches of rain (highest over Sierra)
and valley locations from near 0.10 around Turlock to over 0.60
inches near Redding.

The upper level ridge builds Sunday over the eastern Pacific with
NW-SE jetstream from OR into NV, translating into drier weather
and breezy northerly/offshore winds.        JClapp

&&

.Extended Discussion (Monday through Thursday)

For Monday and Tuesday, models in good agreement that the eastern
Pacific High will be re-established bringing drier weather and a
bit of warming to the region. Patchy dense fog is possible in the
Southern Sac and Northern San Joaquin Valleys Mon-Wed mornings as
the winds become light.

Models really diverge from Wednesday onward. The GFS holds onto a
strong ridge over NorCal through Thursday while the ECMWF has a
trough moving into the west coast that will wipe out the ridge and
bring another round of wet weather. The GEM also holds onto a
strong ridge above NorCal but shows a weather system moving in on
Thursday. For now, have continued to trend toward the GFS and GEM
with a ridging environment for Wed & Thurs until there is better
agreement.  JBB


&&

.Aviation...

A second wave of weather spreading precip into interior Norcal
will spread SEwd into the I-80 corridor after 18Z
Thu. Widespread MVFR with local IFR cigs/vsbys spreading across
NorCal.


&&

.STO Watches/Warnings/Advisories...
None.
&&

$$








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