Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 231650
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
850 AM PST Fri Jan 23 2015

.Synopsis...
Dry weather forecast with areas of night and morning valley low
clouds and dense fog through Monday. Temperatures expected to remain
well above normal through the early next week in fog free areas.
Potential for some light precipitation exists Tuesday into Thursday
of next week.

&&

.Discussion...
Strong upper ridging building over Interior NorCal with clear skies,
light wind, and moist boundary layer resulted in extensive area of
dense fog developing overnight in the Central Valley. Fog product
showing fog and low clouds extend from near Oroville southward
through the Sacramento Valley into the San Joaquin Valley and
westward into the Delta area. Number of observing sites reporting
visibilities below 1/4 mile prompting issuance of a dense fog
advisory which is in effect until 11 am this morning. Remainder of
Interior NorCal should begin experiencing some warming under
increased subsidence today. Some locally breezy easterly wind
occurring in the eastern foothills/mountains this morning under
tightened E-W low level pressure gradient.

Models similar in continuing to amplify strong upper ridge off the
West Coast and building it inland over NorCal through the weekend.
5H heights progged into the middle 580 DM Saturday. MOS guidance
bumping high temperatures into the mid 70s across the Northern
Sacramento Valley Saturday, which is approaching record values.
Extensive night and morning valley fog will continue to moderate
synoptic warming in the Southern Sacramento and Northern San Joaquin
Valleys, where upper 50s to lower 60s expected.

Upper ridge axis shifts through Interior NorCal Sunday with
continued night and morning valley fog and well above normal
temperatures in fog free areas. Locally breezy easterly wind
continues over the weekend into Monday morning for portions of the
eastern foothills/Motherlode and Sierra Nevada.

Models showing omega block over the Intermountain West Monday with
trapped closed low off the Baja coast. As upstream troughing
approaches the West Coast, this low is forecast to begin lifting
towards SoCal. Models spread some higher level cloudiness into the
area, from the south, Monday which, along with lower heights/
thicknesses will bring some minor cooling to the forecast area.

PCH

&&

.Extended Discussion (Tuesday through Friday)

A complex weather pattern is shaping up for the extended period as
the upper ridge shifts to our east. A closed upper low off the
Baja coast this weekend will lift northward, bringing some
subtropical moisture with it. At this point, model guidance keeps
the bulk of moisture to our east, mainly along the Desert
Southwest north into the Great Basin. The Sierra has the best shot
for precipitation Tuesday, but the Valley has been trending drier
in recent runs.

A weak cutoff low then sets up well off the Southern California
coast late next week. Dynamics are quite poor with this system,
but with some residual moisture in place a few showers may be
possible along interior mountains. Longer-range guidance suggests
strong high pressure again building over the West Coast toward
next weekend, temporarily ending the chance for precipitation.

Dang


&&

.Aviation...

Wdsprd IFR/LIFR conds in fog/ST in Cntrl Vly from nr KOVE Swd into
the San Joaquin Vly and W into the Delta area. Conds impvg to mnly
VFR/MVFR by this aftn with wdsprd IFR/LIFR in vly fog/ST agn tngt
into Sat. VFR conds elsw ovr Intr NorCal with lcl gsty Ely winds ovr
the Ern fthls/mtns thru the wknd.

&&

.STO Watches/Warnings/Advisories...
Dense Fog Advisory until 11 am PST this morning in Central and
Southern Sacramento Valley...Carquinez Strait and Delta Area... and
Northern San Joaquin Valley.

&&

$$









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