NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 170606
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1006 PM PST Fri Nov 16 2018


.SYNOPSIS...
Dry with near normal daytime temperatures and cool nights with
heavy smoke due to the Camp Wildfire. Breezy northeasterly winds
over the Sierra Nevada Saturday night into Sunday bringing
critical fire conditions. Cooler temperatures next week with a
series of wet systems through the middle to end of next week.

&&

.DISCUSSION...

Evening Update...Amplified ridging across the NW CONUS continues
tonight. At the surface, light winds and an overnight capping
inversion are keeping smoke and reduced visibilities across most
of the valley tonight. The most recent run of the HRRR near
surface smoke pushes the most dense smoke northward tomorrow
afternoon and evening, which may give some brief period of
alleviation to areas near and south of the Sacramento River Delta.
High temperatures in the eastern valley appeared to be limited by
the smoke with highs topping out in the low to mid-60s. With
similar conditions tomorrow, temperatures are forecast to persist
in the 60s. A wave is still on track to move southeast across the
Great Basin late Saturday afternoon into the evening bringing
windy conditions to areas in the northern Sierra and foothills
bringing critical fire weather conditions to this area.

Previous Discussion...High pressure ridge over the region is
continuing pattern of light winds, smoke with poor visibility and
air quality for much of the area. The smoke is keeping
temperatures below normal blocking heating from the sun during the
day and allowing heat to escape at night, unlike cloud cover.
This brought a cold start in the Valley, with lows down as lows as
the upper 20s and lower 30s. This is about 10 degrees below
normal for this time of year. Highs this afternoon will be a
little below normal in smoke covered areas, near to a little above
normal in the mountains above the smoke. Evacuees from the Camp
Fire should prepare for another cold night and morning. Saturday
during the day should be about the same as today.

Models remain in good agreement in dropping a shortwave trough
southeastward into the Great Basin on Saturday with high pressure
rebounding over the west coast by Saturday night. A tight surface
gradient will develop, bringing gusty northeasterly winds over the
northern Sierra and foothills late Saturday night through Sunday
morning. While not as extensive an area as the event a week ago,
local gusts to 50 mph are possible over northeast oriented canyons
and over exposed ridges. The area impacted includes the Camp
Fire. The Fire Weather Watch has been upgraded to a Red Flag
Warning goes from 10 pm Saturday to 4 pm Sunday for that area.

The main effect of the winds other than increased fire danger
will be a some warming in morning temperatures, due to downsloping
winds Sunday and Monday. Wildfire smoke will continue to be an
issue, and could increase if the Camp Fire increases in activity.
A few high clouds may start spilling into the region late Monday
preceding a possible major change in the weather pattern coming
mid week. EK

&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Given more consistency in recent model guidance, there is rather
high confidence in a pattern change affording multiple
precipitation chances and cooler conditions. The upper ridge
initially parked over the western U.S. will finally adjust
eastward as a southern stream low pushes across SoCal by early
Tuesday. Large-scale troughing emerging from the Gulf of Alaska is
primed to reach the NorCal coast by mid-week. Warm advection
ahead of the trough will spread an initial band of precipitation
into the western zones by early Wednesday morning before spreading
inland. Models have come into better agreement with this initial
feature with uncertainty looming in its wake. The 12Z GFS suggests
a lull in the action ahead of a more impressive shortwave while
the 12Z ECMWF supports continued precipitation chances. Stronger
dynamics accompanying this system suggests heavier amounts with
this frontal passage during Thanksgiving. Given this is a Day 6
forecast, the details of amounts and timing do remain nebulous at
this time. All and all, this significant pattern change will bring
well needed rainfall to the region including mountain snows. This
will ultimately help clear out the stagnant smoky air mass which
has been in place for nearly a week. BRO


&&

.AVIATION...

Light winds along with persistent smoke from the
fire in Butte County have been contributing to reduced
visibilities across the valley. These conditions will continue
through the morning although there may be some improvement by
tomorrow afternoon as the heaviest concentration of smoke stays
confined to Butte County and areas to the north and northwest.
Aircraft reports from this evening state that the top of the smoke
layer resides between 1500-3000 feet.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 10 PM Saturday to 4 PM PST Sunday 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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