Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 251707

Area Forecast Discussion
National Weather Service Sacramento CA
907 AM PST WED NOV 25 2015


Overall winter storm effects decreasing today...but still some
high elevations snow showers today will cause bad travel
conditions at times this afternoon...otherwise look mostly dry
conditions through the holiday weekend.

Large upper low that will be effecting our weather for the next
several days will cause showers today. Most impactful will be
numerous snow showers over the higher terrain which is current in
place over I-80 corridor. Upper wave causing this activity will
slide south this afternoon and should see showers along the crest
mainly around highway 50 and areas south. With pretty poor road
conditions and current snow showers over higher terrain will keep
the winter storm warning going through noon and then let it
expire. Rasch

Center of closed upper low is now over northwest Nevada early this
morning. A potent short-wave dropping down the coast is presently
near the Bay Area and is responsible for generating the area of
showers now moving from the Bay Area into the northern San Joaquin
Valley. Skies have cleared across a large part of the Sacramento
Valley and Coast Range and temperatures in the North Valley have
dipped into the lower to mid 30s. A few showers may linger in the
valley early this morning.

The low will edge slowly into central Nevada today with northerly
flow over NorCal. Additional disturbances moving down from the
north will bring more clouds into the region along with keeping
snow showers going across the northern Sierra. Local additional
snowfall accumulations of 3-6 inches may occur today along the
crest of the northern Sierra.

Northerly surface pressure gradients tighten behind the departing
low tonight and Thanksgiving and locally breezy northerly winds
are expected to develop through the Sacramento Valley. Along with
some cloudiness, this may keep temperatures from lowering too much
tonight, but we`ll monitor the development of the north winds and
amount of clearing during the day with a possible freeze warning
issued later today for the north half of the Sacramento Valley.

Not a whole lot of change expected Thanksgiving heading into the
weekend with cool brisk conditions remaining over NorCal. Flurries
will likely continue across the higher elevations of the northern
Sierra while freeze risk will remain a concern for the Central
Valley during the late night and early morning hours.


The extended forecast is rather uncertain as the blocking ridge
breaks down. The low pressure center portion of the Rex block
ridge has just shifted eastward Sunday into the Intermountain
West, as the next spawned wave from the semi-permanent Gulf of
Alaska Low moves inside 140W. The model differences Monday look
relatively minor in the macroscale; however upon close review,
the GFS brings the approaching wave inside 130W just offshore
from CA/OR border (rainy NorCal), while the ECMWF weakens the
feature and drifts it southward well offshore (dry NorCal). This
transition period from the blocking ridge to more typical
prevailing westerly flow is tricky for the models. Therefore, we
left a mention of potential showers northward and eastward of
Sacramento on Monday.

A couple shortwaves move through the base of the parent trough in
the eastern Pacific on Tuesday and Wednesday. We continued the
mention of chance precipitation, but really need the
Intermountain West ridge to shift more into the Plains in order
to see any significant rain/snow action here. Hurry up and
wait...for the precipitation.           JClapp



Showers and VFR cloudiness moving SE over northern San Joaquin
Valley thru about 12z. Showers to redevelop over Sierra today as
upper low lingers over NV. Fog not a huge concern this morning
due the Low pressure in area; just some ground fog with minimal
restrictions. Flight level 10k MSL north winds 20-35kts with
strongest northward of Sac metro area.           JClapp


.STO Watches/Warnings/Advisories...
Winter Storm Warning until noon PST today for West Slope
Northern Sierra Nevada.

Freeze Watch from late tonight through Thursday morning for
Central Sacramento Valley-Northern Sacramento Valley.


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