Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 232257
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
357 PM PDT Tue Sep 23 2014

.Synopsis...
Dry and warm temperatures continue today. Cooler and wetter
weather expected for the middle to end of the week.

&&

.Discussion...
Satellite imagery shows increasing mid to high level clouds ahead
of a cool and moist Pacific storm which will signify a shift to
more fall like weather. Southwest flow ahead of the approaching
Pacific storm will create breezy winds again tomorrow and possibly
exacerbate conditions near wildfires in the Sierra Nevada.

Models have been trending the storm wetter and slightly slower
over the last several runs. The latest iteration of the medium-
long term models show the trough digging and attempting to cutoff
from the main westerly flow during the weekend. The result of this
is that the upper low is forecast to linger over CA/NV through
most of the weekend, rather than eject out by the end of the
workweek. Temperatures will now remain below normal through the
weekend, and lingering showers are increasingly likely after the
main precipitation push. We are relying more so on pattern
recognition than model guidance for timing/placement of convection
once the core of the low shift onshore Friday into Saturday.

Precipitation is expected to begin in the northern Coastal Range early
Wednesday before transitioning further south and east into
Thursday. Latest quantitative precipitation estimates suggest over
1.35" at Shasta Dam, with similar values in the Shasta-Trinity
National forest. Elsewhere, expect less precipitation, especially
in the valley where only a few hundredths may be observed. At this
point, precipitation amounts near the King fire do not appear
very significant (no more than a quarter of an inch), but the cool
and moist Pacific air mass should help containment efforts once
the airmass shifts over the area Thursday. DRP

&&

.Extended Discussion (Saturday through Tuesday)

Upper level trough over the area Saturday will continue below
normal temperatures and a threat of precipitation...mainly over
the mountains. Thunderstorms are also possible over the Northern
Sacramento Valley and mountains Saturday afternoon. Temperatures are
expected to be in the upper 70s to low 80s in the valley and 50s
and 60s in the mountains on Saturday which are about 5 to 10
degree below normal for this time of year. Confidence is still low
how quickly the trough with move out of the area, with the GFS
lingering on Sunday and the ECMWF east of the area by Sunday
afternoon. The forecast lingers showers over the Shasta County and
down the Sierra on Sunday with the trough gradually shifting east.
Another system digs into the Great Basin early next week bringing
some clouds and keeping temperatures near to a little below
normal.


&&

.Aviation...

Generally VFR/MVFR conditions with mid and high clouds moving in
as upper level trough approaches and smoke from King Fire spreads
North over the area bringing local IFR/MVFR conditions. Increasing
winds this afternoon with local surface wind gusts up to 32 kts
over the ridges and through the delta. Deteriorating conditions
expected at TAF Sites with low clouds and areas of MVFR conditions after
18z Wednesday into Thursday morning as system moves into the area.
Smoke will continue to bringing local IFR/MVFR conditions on Wednesday.

&&

.STO Watches/Warnings/Advisories...
red flag warning until 8 pm pdt wednesday burney basin / eastern
shasta county...west slope northern sierra nevada...western
plumas county/lassen park.

&&

$$







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