Area Forecast Discussion
Issued by NWS Sacramento, CA

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548
FXUS66 KSTO 302201
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
301 PM PDT FRI SEP 30 2016

.SYNOPSIS...
Continued cooling expected through the weekend with daytime highs
15 to 25 degrees below normal by Sunday. Chance of rain and snow
showers Sunday into Tuesday with isolated thunderstorms more
Sunday/Monday. Warmer and drier by mid week with another chance
of showers for northern mountains by Friday.

&&

.SHORT TERM DISCUSSION (Tonight through Monday)...
Temperatures are running roughly 5-15 degrees below Thursday
readings as the early season low pressure system from the Gulf of
Alaska continues to drop southeast into the eastern Pacific. The
cooler air will continue filtering into the region over the
weekend. The Delta Breeze was relatively strong today with winds
at Travis AFB sustained at around 20 knots with gusty ridgetop
winds as well over the mountains. Winds may be slightly lighter
Saturday as NorCal sits between two wave. Winds will increase
again Sunday associated with the next (main) wave and front. This
wave and associated frontal band is has been consistently progged
by the models to move through NorCal during Sunday afternoon
moving into the Sierra late afternoon or evening. Snow levels may
drop below pass levels with a few inches of snow accumulation
possible Sunday afternoon and overnight. Not all snow will stick
to the roads. But since this could be a highly traveled period, we
decided to issue a Winter Weather Advisory for the Sierra Nevada
and Lassen Peak above 6000 feet.

Models show enough instability for a chance of thunderstorms, but
a lot will depend on timing of the front and coincidence with
daytime heating. Cloud cover and cooler airmass will bring another
big drop in temperatures Sunday with daytime highs in the valley
mainly in the 60s or about 20 degrees below normal. The upper low
moves into the Great Basin on Monday and this should bring an end
to much, if not all, the precipitation threat to most areas.
Building high pressure will bring warmer temperatures.   JClapp

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)
Early Tuesday a wave will be approaching Northern California that
is expected to weaken as it moves inland. Models are in agreement
that some light precipitation could fall early Tuesday along the
coastal range, Northern Sacramento Valley, and northern mountains
but precip chances decrease as you move south and east. Things
begin to dry out Tuesday afternoon and evening as a weak ridge
quickly builds in behind this wave.

Wednesday looks dry for Northern California with temperatures
rebounding to the lower 80s for the Central Valley. On Thursday,
the ECMWF brings in another trough to Northern California while
the GFS/GEM delays it until Friday. The ECMWF brings in a much
deeper trough while the GFS just skirts Northern California which
would likely result in no precipitation for our area. For now, we
have gone in the middle of the road and have a slight chance of
showers in the northern valley/mountains on Friday while keeping
the rest of our area dry.    Wilson

&&

.AVIATION...
VFR conditions will continue across the valley these next 24
hours. Winds will be lighter Saturday with the strongest winds
near the delta and gusting up to 20 kts. Fair skies will continue
until a system moves onshore Sunday. Wilson

&&

.STO Watches/Warnings/Advisories...
Winter Weather Advisory from 11 AM Sunday to 5 AM PDT Monday for
West Slope Northern Sierra Nevada-Western Plumas County/Lassen
Park.

&&

$$



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