Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 241723
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
923 AM PST Sat Jan 24 2015

.Synopsis...
Dry weather with areas of night and morning valley low clouds and
fog through Monday. Temperatures expected to remain well above
normal through early next week in fog-free areas. Light
precipitation is possible Tuesday and Wednesday next week.

&&

.Discussion...
High pressure aloft centered just off the NorCal coast is forecast
to strengthen over the region today. Strong inversion over the
Central Valley still resulting in extensive fog and stratus
through much of the valley (up to just south of Chico this morning
- tops are around 1000 ft). Skies are clear except for the valley
fog and most visibilities in the fog areas are around 1/4 or
better, but a few lower visibilities continue so we`ll keep the
dense fog advisory going for now.

Offshore gradients have strengthened compared to 24 hours ago and
are now up to around 9.5 mbs from Reno to Sacramento. Some breezy
north to east winds are occurring just above the inversion with
local gusts in the 30-40 mph range, so there`s hope for an earlier
dispersion of the stratus through much of the area. Strong
offshore gradients forecast to continue tonight and Sunday and
model cross-sections point toward shallower inversions tonight and
Sunday. We`ll continue to monitor and may update for milder temps
if we clear out earlier than expected.

&&

.Previous Discussion...
A strong upper level ridge is centered over the eastern Pacific
and shifting eastward toward California. Skies are mostly clear
across the area, except for the persistent low clouds and fog that
is covering much of the Central Valley from Chico to south of
Fresno. This fog is locally dense in spots, and a dense fog
advisory will continue through late this morning for those
locations. We are seeing some locally breezy north/east winds over
the mountains, but they are of relatively little impact.

As high pressure builds into the area, locations that remain fog-
free (Northern Sacramento Valley, mountain locations) will be
experiencing unseasonably warm conditions this weekend. NAEFS
ensembles show that the Northern Sac Valley in particular will see
highly anomalous temperatures...they could be within a degree or
two of high records. Farther south...the fog will again be slow to
erode, with some locations not clearing out until the afternoon
today (if at all). From about Yuba City southward, highs will
remain around or below 60 degrees today, and perhaps a bit warmer
Sunday.

The upper ridge shifts east of California on Monday, with some
synoptic cooling expected that day. We should also begin to see
increasing high cloud cover later on in the day as a system off
the Baja California coast moves northward.

Computer models are finally coming into better agreement on the
track and timing of this system. Looks like some precipitation
will be possible along the Sierra beginning late Monday and
spreading northward on Tuesday. Snow levels are currently expected
to be around 6000-7000 ft, but only minor snow accumulations are
expected. The Valley has lower odds of seeing precipitation, but
can`t completely rule out a sprinkle or light shower. Dang

&&

.Extended Discussion (Wednesday through Saturday)...
Remnants of weak upper low forecast to move out of Southern
California early next week forecast to be somewhere over the
northern Great Basin by early Wednesday. This will bring a slight
threat of light showers to the northern mountains and Sierra
Cascade range but this threat will end quickly as high pressure
pushes back northward over the west coast. Despite variable cloud
cover on Wednesday, daytime highs are expected to remain a few to
several degrees above normal under warm airmass under the ridge.
Extended models show another upper low setting up off the Baja
coast by Thursday similar to the system forecast for earlier in
the week. This system would likely begin spreading high cloudiness
over the north state as early as Thursday but daytime highs still
likely to climb a bit under upper ridge and light northerly winds.
The upper low off Baja is forecast to slowly shift inland Friday
and Saturday remaining over Socal and the southwest U.S but may be
able to spread a few very light showers northward up the Sierra as
far north as Tahoe. The rest of the forecast area will see
variable high cloudiness going into next weekend with daytime
highs remaining well above normal under upper ridging along the
west coast.

&&

.Aviation...
Valley Low clouds/fog south of about KCIC with IFR/LIFR conditions
expected through about 19Z. Then conditions gradually improving
through 21Z. Sutter Buttes exposed through fog indicates cloud
tops between 010 and 015. Low clouds/fog returning tonight, but
may stay mostly south of Sutter Buttes. Elsewhere, VFR. Light
winds foggy areas, otherwise north to east winds 5 to 15 knots
with gusts to 25 knots over Sierra. JClapp

&&

.STO Watches/Warnings/Advisories...
dense fog advisory until 11 am pst this morning carquinez strait
and delta...central sacramento valley...northern san joaquin
valley...southern sacramento valley.

&&

$$




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