Area Forecast Discussion
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FXUS66 KSTO 160646

Area Forecast Discussion
National Weather Service Sacramento CA
1045 PM PST Thu Nov 15 2018

Dry with near normal temperatures through early next week except
in areas of heavy smoke due to the Camp Wildfire. Breezy
northeasterly winds over the Sierra Nevada Saturday night into
Sunday elevating fire danger. Cooler temperatures next week with
increasing chances of precipitation across interior Norcal by mid-


Evening Update:  Pilot report out of SMF late this afternoon had
tops of the smoke layer about 5 kft. Roughly have to get to that
elevation to get "on top" of the smoke. With very light winds and
limited mixing heights over the area on Fri, generally don`t expect
a significant change in the smoke over most of the area on Fri. The
exception may be on the W side of the Nrn Sac Vly on Fri as
tonight`s short wave over the RDD area (bringing a patch of high
cloudiness with it) may have a tendency to turn the winds NWly
behind it, but confidence is low because of the weak/weakening
nature of this short wave.

HRRR smoke loop showed the heavier concentrations of smoke on the E
side of the Vly drifting a little to the W during the night given
the downslope/Ely flow over the Sierra. VSBYS will continue to be
restricted in the Vly given lack of mixing and with very light winds
on Fri. The smoke really had an impact on max temps today with the
highs from 55-62 under the thick smoke cover and readings in the mid
to upper 60s around it.  JHM

.Previous Discussion...
A strong dome of high pressure over the eastern Pacific and west
coast will bring dry conditions across the region. Temperatures
should be below normal over most locations outside of mountain
locales given heavy smoke spreading from the Camp Fire. Reduced
solar insolation from wildfire smoke in these locations will keep
daytime highs over the next couple of days below normal for this
time of year. The other impact of this wildfire smoke will be
decreased visibilities throughout the central valley impacting
aviation. At this time, the worst area of visibility is around
Oroville and Yuba City regions where visibilities are reported at
1/2 mile. Smoky valley conditions are likely to continue Friday and
possibly even Saturday given light winds and stable atmospheric
Models in fairly good agreement in dropping a shortwave trough
southeastward through the Pacific Northwest into the Central Great
Basin on Saturday with high pressure rebounding over the west
coast by Saturday night. The combination of northeast to easterly
flow aloft and a tight northeast surface gradient across the
Sierra will bring breezy northeast winds Saturday night especially
to the higher elevations and favorably oriented Sierra and
foothill canyons. These breezy winds will bring elevated fire
danger will be short lived with winds decreasing by Sunday
afternoon. As such, a Fire Weather Watch is in effect for these
mentioned locations, including the Camp Fire. The brief wind
event may be sufficient enough to mix some of the smoke out of the
valley on Sunday so this region may see a little more sun during
the second half of the weekend.


Increasing potential for measurable rainfall sometime during the
middle to latter part of next week.

The upper ridge is forecast to progress into the Central Great
Basin Monday while split flow ensues across the eastern Pacific.
The latest guidance depicts one upper low shearing across SoCal
on Tuesday while a broader scale trough looms farther offshore.
At this point, medium range models continue to diverge with the
timing of this system. The European has been consistently ahead
of the GFS carrying the short wave trough into NorCal Wednesday
with ridging returning by the following day, while the GFS
maintains upper ridging. GEFS and NAEFS ensembles show upper
troughing similar to European, but slower progression with the
wave moving inland on Thanksgiving. As mentioned above, rainfall
chances will be on the increase by the middle of the week, albeit
with significant timing uncertainty.


Winds continue to remain fairly calm with smoke continuing to impact
the entire Sacramento Valley. Visibilities will range from MVFR to
LIFR with little improvement through the period. Mid-afternoon PIREP
over KSMF had top of the smoke layer at 5kft.


Fire Weather Watch from Saturday evening through Sunday
afternoon for Northern Motherlode From 1000 to 3000 Ft. Includes
portions of Nevada-Yuba-Placer-Amador and ElDorado Units-
Northern Sierra Foothills from 1000 to 3000 Ft. Includes
portions of Shasta-Trinity and Butte Units-Northern Sierra
Including Lassen NP and Plumas and Lassen NF/S West of the
Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)-
Northern Sierra Including the Tahoe and ElDorado NF/S West of
the Sierra Crest.


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