Area Forecast Discussion
Issued by NWS Sacramento, CA

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958
FXUS66 KSTO 162305
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
305 PM PST Fri Feb 16 2018

.Synopsis...
Dry and milder weather through Saturday. Next system brings a
chance of showers to mainly the mountains on Sunday followed by
cold temperatures early next week with a possible widespread
freeze.

&&

.Discussion...
Dry and mild weather will continue into Saturday with lighter
north wind. Ridging deamplifies by Saturday night as troughing
pattern sets up over the West Coast for next week. A weak system
will drop southeast in the flow, bringing some light
precipitation to the mountains Sunday afternoon into Monday.
Breezy winds and much colder air will also filter in. This will
drop snow levels to around 1000 feet by Monday, with a few inches
of accumulation possible at pass levels and a dusting down to
around 1500 feet. This may be enough to cause some slick roads and
minor travel delays for the holiday weekend, but not expecting
major impacts.

Main story will be the big cool-down for Sunday into next week.
Overnight temperatures Sunday night into Monday will drop to near
the freezing mark across the valley with areas of a frost and the
possibility of a widespread freeze. Mountain temperatures will be
in the teens. Slightly lower confidence in temperature forecast
this night though due to cloud cover from system and lingering
breezy winds. Coldest nights look to be in the extended period.
Regardless, given potential agricultural impacts from recent warm
temperatures and early bloom, have issued a freeze watch for
areas below 2000 feet beginning late Sunday night. This continues
into extended period.

CEO

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)
Main concern during the extended period will be overnight lows
several degrees below normal as a trough along the West Coast
advects cold air into the region. Tuesday morning low temperatures
are expected to be below freezing throughout much of the Central
Valley resulting in areas of frost and potential damage to early
budding plants. Moreover, strong anomalies support these cold
temperatures, including -2 standard geopotential height anomalies,
and -3 or lower anomalies at 850mb temperatures. Thus, a freeze
watch is in effect through Wednesday morning.

Unseasonably low heights along the West Coast will allow for
additional upper disturbances to push across the area Wednesday
through Saturday. The latest ECMWF run indicates a wetter and
deeper scenario with these waves, whereas the GFS keeps
precipitation chances confined to the mountains. Thus, have
introduced a slight chance of precipitation over the mountains,
but confidence remains low.


&&

.AVIATION...
VFR conditions over Interior NorCal next 24 hrs with surface
winds below 12 kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late Sunday night through Wednesday morning
for Carquinez Strait and Delta-Central Sacramento Valley-Clear
Lake/Southern Lake County-Motherlode-Mountains Southwestern
Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Shasta Lake Area / Northern Shasta County-
Southern Sacramento Valley.

&&

$$



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