Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Sacramento, CA (STO)

FXUS66 KSTO 171135

Area Forecast Discussion
National Weather Service Sacramento CA
335 AM PST Mon Dec 17 2018

Weather system exits to the east today with drier weather
returning for much of the region. The exception will be the far 
northern portion of the state which will continue to see 
precipitation through Tuesday. Another weather system will bring a
chance of light precipitation by the end of the week.


Rain continues across the southeastern half of the forecast area
early this morning as the frontal system slowly progresses through
the region. Precipitation amounts over the past 12 hours have been
generally around an inch across the Central Valley with 1 to 2
inches over the northern mountains. The front has been slow to
make it into the northern Sierra so far and amounts there have
been generally under half an inch.

Winter storm warning has been downgraded to an advisory across the
northern Sierra as snow levels have been slow to lower. A quick
shot of snow near the pass levels will be possible this morning
before precipitation tapers off by this afternoon. The main part
of the system clears the valley early this morning.

Ridging builds into NorCal in the system's wake for a return to 
dry weather for much of the region. The exception will be the far 
northern portion of the forecast area where warm-advection ahead 
of the next system moving into the PacNW will continue 
precipitation into Tuesday.

A third system will drop down in northwest flow later Thursday
bringing another chance of light precipitation to NorCal.


The longwave pattern across the Central/Eastern Pacific continues
to churn out a series of systems which take aim at the West 
Coast. Sorting out the finer details of each particular system 
will remain a challenge, particularly in light of the ensemble 
model spread.

After a wet conclusion to the work week, the beginning of the
weekend should be dry across the region. Impacts from the next
Pacific shortwave trough are expected to move through as early as
late Saturday night. However, there are not only differences
between the GFS and ECMWF models, but they also exhibit
uncertainty on a run to run basis. While not a wash out by any
means, daily chances for precipitation are likely into Sunday as
well as Christmas Eve. It is worth noting these systems currently
lurk out over the Western Pacific so much can change in the
upcoming days. High temperatures throughout the period should 
stay close to mid/late December climatology. Mid to upper 50s 
across the Valley and low to mid 40s over mountain locales.  BRO


Precipitation will gradually end at Valley locations around 12Z- 
14Z, with activity continuing across the Sierra through 21Z-23Z. 
Widespread MVFR/IFR conditions will continue at TAF sites through 
late this morning; improving to VFR in the afternoon.


Winter Weather Advisory until 10 AM PST this morning for West 
Slope Northern Sierra Nevada.