Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 041159

Area Forecast Discussion
National Weather Service Sacramento CA
359 AM PST Sun Dec 4 2016


A small upper level disturbance will bring chances for small
amounts of rain and snow to the upper Valley and northern
mountains Sunday into Tuesday. Colder air in the Valley could
result in near to below freezing overnight temperatures this
coming week.


.DISCUSSION (Today through Wednesday)...

Water vapor imagery and model analysis data showed the influence
of an upper level high pressure system over the eastern Pacific
begining to erode as a weather disturbance approached the region
from the northwest overnight. Increasing moisture ahead of the
disturbance on IR satellite imagery showed increasing high level
cloud cover moving into the northern mountains and northern Sacramento
Valley, and these clouds will continue to filter into the forecast
area through the morning.

Model forecasts are still in good agreement and on track to pass
the small disturbance through the Pacific northwest tonight into
Monday morning, and some precipitation will skirt along the
northern most portions of the forecast area bringing snow to
elevations higher than 2500 feet and rain to portions of the
northern Sacramento Valley. Little to no snow accumulations are
expected since most of the associated moisture with the system
will remain to the north. Elsewhere across the valley, patchy fog
is possible with patchy freezing fog in higher elevations with
temperatures below freezing Monday morning.

Northwest flow aloft will bring in colder below normal
high and low temperatures to the forecast area through mid week,
which will range between 5 and 10 degrees colder than average.
Confidence is increasing that temperatures Tuesday night into
Wednesday morning will be near or below freezing, which could
result in damage to crops and sensitive vegetation for locations
near or below 32 degrees.

Another disturbance is forecast to move through northern
California for more chances for rain and snow Tuesday and
Wednesday night. Light snow accumulations between 1 and 2 inches
are expected for the mountains and rain chances for the Valley.


Precipitation chances expected to increase across the region
Thursday and Friday as upper ridge shifts east allowing an upper
trough to move through. Models show potential for some significant
QPF for NorCal as system interacts with moisture moving across
the Pacific. weak ridging next weekend may allow for drier weather
for a few days.

Cool temperatures expected Thursday as cold air remains trapped
across NorCal from earlier in the week, but increased mixing
expected to bring moderating temperatures by next weekend.



Light and variable flow expected to continue at the surface for
the next 24 hours as weakening frontal system moves south into
NorCal after 00Z Monday. Areas of MVFR with local IFR conditions
BR/FG in the Central Valley thru about 17Z, otherwise VFR next 24



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