Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 201748
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
948 AM PST Mon Feb 20 2017

.SYNOPSIS...A storm system moving into central and northern
California will bring high elevation snow to the southern Sierra
Nevada and White Mountains through Tuesday. Lighter precipitation is
possible across the southern Great Basin. Breezy conditions are
expected at times through mid-week with cooler temperatures
occurring during the second half of the week.
&&

.UPDATE...Visible satellite loops and surface observations showed
extensive low to mid cloud layers across most of the forecast area
except western and southern San Bernardino County and this coverage
will remain largely unchanged through the day. Substantial
moisture was moving into the southern Sierra. There is decent
spillover occurring as automated gauges in the Owens Valley near the
Sierra foothills had recorded 0.15-0.25" of rain in the past 3 hours
while the Bishop Airport had only picked up 0.02". Aspendell has
picked up 5.5 inches of snow so far and it will continue this
afternoon and evening. The going forecast has these trends
fairly well covered but made some tweaks to increase PoP values and
adjust QPF for the Owens Valley. -Adair
&&

.AVIATION...For McCarran...It appears CIGS around 5 kft may become
scattered by early afternoon based on latest satellite and
surface observation trends. A SSE wind component will transition to
be more from the south after 20Z and speeds will increase with gusts
up to 22 kts between 21z and 02z.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Rain and high elevation snow mainly over northern Inyo
County today with lower CIGS and mountains obscured. Elsewhere, CIGS
will range between 5-7 kft except in southeast California south of
I-40 where skies were mostly clear. Southerly winds will increase
areawide with gusts 20-25 kts for KBIH and across southern central
Nevada.
&&

.PREV DISCUSSION...
335 AM PST Mon Feb 20 2017

.SHORT TERM...through Wednesday night.

Trough over the eastern Pacific driving a narrow atmospheric river
of moisture with precipitable water values approaching 1.50" into
the central California coast this morning. Heaviest precip will
occur under this band from the Bay Area inland into the central
Sierra today. Moist orographic flow will enhance precip on the west
side of the southern Sierra with lighter amount spilling over the
crest into Inyo County, including the Owens Valley. The moist flow
will continue into Tuesday before starting to weaken. More
uncertainty exists among the models in just how much light precip
makes it east of the Sierra`s into the southern Great Basin. Did not
make much change keeping at least a chance in the Spring
Mountains/Sheep Range and the counties across south central Nevada.
Snow levels still looking quite high during the main event through
Tuesday with levels staying above 7000-7500 feet in Inyo County. For
the southern Great Basin it will mostly be a rain event with snow
levels ranging between 8000 and 9500 feet today and Tuesday. The
Winter Weather Advisory remains in effect from the easter Sierra
Slopes and White Mountains through 10 am PST Tuesday.

The trough will move into California and the Great Basin Wednesday
through Wednesday night. Again there is some uncertainty regarding
precip coverage as models QPF placement not the greatest. Due to the
uncertainty left highest POPS in for the south central Nevada
Counties and northern Mohave County.

Breezy to windy from the south/southwest today and Tuesday. Gusty
westerly winds will continue across the Mojave Desert Wednesday with
an eventual shift to a northerly direction Wednesday night following
a cold frontal passage.

Extensive cloud today will likely inhibit high temperatures so
trimmed a few degrees off the previous forecast. Tuesday still looks
like the warmest day with values falling back closer to normal
Wednesday as trough enters the Great Basin.

.LONG TERM...Thursday through Sunday.

Broad troughing will persist across the western states Thursday and
Friday with our region underneath a brisk northwest flow. This will
lead to continued cool and breezy conditions, with only very low
shower chances confined to the higher terrain of the Sierra and
southern Great Basin. Temperatures area wide will remain several
degrees below average.  Another storm system will begin to dig down
southeast Saturday and Sunday, but there are differences among the
model guidance as to how vigorous this energy will be. If it digs
down the west coast, it would result in a more significant influence
and wetter weather, while if it remains a more open wave it would
tend to be drier.   For now, continued cool temperatures and
mountain showers look like the most confident outlook, and it will
continue to be a period that is monitored in the days ahead.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

$$

Update/Aviation...Adair
Short Term...Pierce
Long Term...Outler

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