Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 231043
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
243 AM PST Sat Feb 23 2019


.SYNOPSIS...
Wet weather returns to northern California this weekend and will
continue into next week.

&&

.DISCUSSION...
The forecast remains on track this morning as clouds continue to
stream into the region. This cloud cover will primarily cover
northern portions of the CWA which should inhibit frost from
forming. Farther south, in the central Sacramento Valley and
northern San Joaquin Valley, recovering dewpoints and clear skies
could lead to some patchy frost development. As the day continues,
cloud cover will continue to spread over the region and chances
for precip will increase. Most of the rain and mountain snow will
be confined north of the 50/80 corridor and primarily effect the
northern portion of the Sacramento Valley. Snow levels will
initially range from 2500 ft in the Shasta County mountains to
near 4000 ft over the "Coastal Range". Impact wise, travel along
highway 299 may be difficult at times since several inches of
snow will accumulate, especially as we head into tonight and
Sunday. Precip continues into Sunday and will eventually spread
over the southern half of the CWA as this system taps into a weak
AR.

From Sunday nite into the middle of next week, precip will
become become steadier and heavier over northern California. The
West Coast AR Landfall Tool implies that this moisture plume (AR)
will impact Norcal through the 27th (Wed). For the 80/50
corridor, precip is forecast to move into that area early Monday,
and should become heavy over the Hwys 70/36 corridors by Monday
afternoon. Winds will also be increasing Mon and Tue as the bulk
of the AR moves inland. The WAA from the AR will raise snow levels
to at least 5-6 kft, if not higher over the Sierra.

The timing of the weather systems, duration of the AR, and the
relatively low snow levels initially, followed by rising snow levels
during the event, warrants segmenting the WSW product. Not the
easiest way to handle this, but the different areas will be impacted
differently, both in time and quantity of precip. After snow levels
rise above 5 kft, there is little impact for zones 13 and 63, while
impacts continue for the Sierra. The runoff from the precip through
the middle of next week will cause rivers to rise, so expect some
hydro impacts as well.  JHM/KR

&&


.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

The forecast remains on track, with an active weather pattern
continuing to look likely for the extended portion of the
forecast. QPF amounts on Wednesday suggest less than 1" across
the area. Hazardous mountain travel is anticipated, with snow
levels around 5,500 to 6,500 feet. Forecast models disagree with
how quickly to eject this system on Thursday, with the ECMWF being
more progressive. Thus, lingering mountain showers could be
possible on Thursday. Otherwise, dry conditions are expected for
most areas as weak ridging develops between systems. A return of
precipitation is likely late Friday into next weekend as the next
system approaches from the west bringing widespread precipitation.
&&

.AVIATION...

VFR conditions predominate next 24 hours with generally light
winds. Areas of MVFR possible with light precipitation over the
Coast Range and north of KRDD after 00Z Sunday.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from this evening through Tuesday morning for
Burney Basin / Eastern Shasta County-Mountains Southwestern
Shasta County to Northern Lake County-Western Plumas
County/Lassen Park.

Winter Storm Watch from Monday morning through Wednesday morning
for West Slope Northern Sierra Nevada.

Winter Storm Watch from this evening through Monday morning for
Shasta Lake Area / Northern Shasta County.

&&

$$


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