Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 210451
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
951 PM PDT Sat Sep 20 2014

.Synopsis...
Lingering Sierra showers/t-storms are possible through the
weekend, otherwise, dry & warmer temperatures into early next
week. Cooler and wetter weather arrives middle of next week into
next weekend.

&&

.Discussion...
Instability advected into the srn sac/san joaquin valley earlier
this evening. This touched off isolated showers and thunderstorms
over the area. Activity has diminished over the past few hours
with a few isolated showers over the valley although a new batch
of convection is developing over the southeastern Sierra. Have
increased overnight pops over the southern portion of the area...as
HRRR maintains showers and isolated thunderstorms through sunrise.

.Previous Discussion...
Satellite imagery shows a cut off 578dm closed low centered
directly over Oxnard as of 230pm this afternoon. This closed
circulation center is positioned directly below the apex of a
ridge extending across much of the western US. Short term
convective guidance has varied, with the NAM12 over analyzing
convection, the WRF keeping the convection along the higher
terrain of the Sierra, and the HRRR spilling convection into the
valley from the south and east. The most plausible scenario is a
blend between the WRF and HRRR solutions with most of the
convective activity occurring along the crest, with a low to
moderate probability of spill over into the foothills and valley.
The best chance for spillover into the valley is between 9pm and
3am tonight. The best chance for rainfall is late today and
overnight when a moist PW plume interacts with the enhanced
northeastern sector of the upper low and orographics of the
Sierra. A third of an inch of rain is possible above 4000 feet
south of Lake Tahoe should nature play out as modeled. KDAX radar
indicates the first cell has developed south of SR108 in Tuolumne
county over the last 10 minutes. Elsewhere, mid to high clouds
have been streaming in around the upper low and have helped to
moderate temperatures slightly.

The upper low is forecast to shift inland and slowly reintegrate
with the mean westerly flow over the next few days. Temperatures
will remain near normal through the short-term with upper 80s to
low 90s in the valley. A gradual cooling and drying trend is
expected into early next week.

Smoke from the King Fire will continue to impact the Sierra and
foothills into the adjacent Southern Sacramento valley. Hazy
conditions surrounding the smoky area will extend into the Central
Sacramento valley into the Northern San Joaquin valley. On Sunday,
the general wind pattern transitions to a weak onshore flow which
should push smoky/hazy conditions eastward. DRP

.Extended Discussion (Wednesday through Saturday)

Upper level trough along the west coast on Wednesday and moves
onshore later in the week bringing cooler temperatures and a
chance of precipitation. The models vary with the timing of the trough and
track of the low so confidence is low in the timing and coverage
of precipitation. The GFS moves the system through Thursday into
early Saturday and the ECMWF is slower and forms a low over the
Pacific Northwest on the weekend. Showers may start as early as
Wednesday over the coastal range and spread over the area on
Thursday...mainly north of Interstate 80. Showers may continue on
Friday and Saturday...especially over the mountains. Temperatures will be
in the 80s in the valley and 60s and 70s in the mountains on
Wednesday and drop down to the mid 70s to low 80s in the Valley
and 50s and 60s in the mountains on Thursday and Friday. These
temperatures are near to around 5 to 12 degrees below normal for
this time of year on Thursday and Friday.


&&

.Aviation...

VFR conditions the next 24 hours all TAF sites. MVFR/IFR
visibilities east of SAC into the foothills and mountains due to smoke
from the King Fire. Isolated Thunderstorms possible along the
Sierra.

&&

.STO Watches/Warnings/Advisories...
None.
&&

$$







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