Area Forecast Discussion
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FXUS66 KSTO 161152

Area Forecast Discussion
National Weather Service Sacramento CA
352 AM PST Fri Nov 16 2018

Dry with a little above normal daytime temperatures through early
next week except near or cooler than normal 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 middle to end of next week.


High pressure over the eastern Pacific and western U.S. will keep
the forecast area dry through the short term period. A light east
flow out of the Sierra and a light northerly flow down the
northern Sacramento valley combined with stable conditions under
the ridge will again concentrate smoke from the Camp Fire into
the central valley today. Main concentration of smoke will be
from southern Tehama county southward to Stanislaus county. In
this region, daytime high temperatures will be limited by lack of
sunshine keeping them near or even several degrees below normal.
Other impact will be reduced visibilities in this region with
current morning reports dropping visibility to 1/2 mile some local
spots. Only minor changes are expected in the weather pattern on
Saturday so smoke is likely to remain concentrated into roughly
the same areas. Although smoke seems to be blocking solar
insolation enough to cool temperatures during the day, radiational
cooling at night is allowing valley temperatures to drop down into
the 30s or about 5 to 8 degrees below normal.

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 through
Sunday especially to the higher elevations and favorably oriented
Sierra and foothill canyons. These breezy winds will bring
elevated fire danger and a fire weather watch will remain in
place for the Sierra and Foothills Saturday evening through Sunday
afternoon. The breezy winds may bring enough vertical mixing to
reduce the central valley smoke but the winds in the valley will
not be all that strong so some of the smoke concentration is
expected to remain. The main effect other than increased fire
danger will be a little warming in formally very smokey areas
Sunday where smoke amounts are reduced.

Upper ridge axis will shift just east of the forecast area by
Monday afternoon bringing a slight cooling most areas. Central
valley smoke will still be a wild card but with relatively light
winds under the ridge believe that at least light smoke will
remain in the valley. A few high clouds may start spilling into
the region late Monday preceding a possible major change in the
weather pattern coming mid week.


Confidence in increase in a pattern change this week, bringing
cooler temperatures and a chance of precipitation mid- to late-
week. Models continue to show a split flow pattern Tuesday, with
one upper level low moving over SoCal while a deeper upper low
moves east over the eastern Pacific. The most recent GFS run is
nudging closer to the Euro`s progression, though timing
inconsistencies still remain. In general, a shortwave trough and
associated cold front is forecast to move inland Wednesday,
bringing with it a chance of precipitation and cooler daytime
temperatures. Showers could linger behind the shortwave Thursday
before another low pressure system moves onshore Thursday evening
through Friday, bringing another wave of precipitation to NorCal.
Precipitation timing and amounts are still uncertain at this time
due to model inconsistencies this far out. Stay tuned to to the
forecast for any updates. HEC



IFR conditions continue for the Central Valley with MVFR
conditions for the Northern Sacramento Valley due to smoke from
the wildfire in Butte County. Winds have been fairly stagnant,
allowing localized LIFR conditions in the Sacramento area.
Winds generally less than 10 kts. HEC


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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