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FXUS65 KVEF 190351

Area Forecast Discussion
National Weather Service Las Vegas NV
751 PM PST Wed Jan 18 2017

.SYNOPSIS...The first in a series of wet storm systems will push
across the region tonight and Thursday. This will be quickly
followed by a second system Friday into Saturday and yet another
Sunday into Monday. These storms will bring significant snow
to the mountains and rain to the deserts. 

.UPDATE...Light rain had pushed into Inyo and western San Bernardino
counties this evening, with a few showers in the Spring Mountains as
well, but probably only virga in the Clark County valleys thus far.
Rain will continue spreading east overnight, as reflected in the
previous forecast. No update planned this evening.

255 PM PST Wed Jan 18 2017

.SHORT TERM...tonight through Friday night.

Two Pacific storms are still on track to impact much of our region
tonight through Friday night. The base of the first trough was
located just off the central California Coast and an extensive
moisture plume could be seen spreading across California and Nevada.
This moisture will head our way as the trough digs and quickly moves
inland tonight and Thursday across southern California and the
Mojave Desert Region as an open wave. Radar loops showed
precipitation beginning to reach the southern Sierra as of this
writing but precipitation also extended down to near Santa Barbara
and a band is forecast to expand from southwest to northeast across
San Bernardino County into southern Nye County and the Spring
Mountains by late this evening. This will continue moving across
southern Nevada and northwest Arizona overnight and looks like it
will be followed by a secondary band Thursday morning through
afternoon just ahead of the trough axis which is forecast to move
over southern Nevada by late Thursday afternoon. Isolated
thunderstorms will be possible across the Mojave Desert zones,
including the Las Vegas Valley. Precipitation will taper off from
west to east on the back side of it and will see a brief break
through early Friday. Snow levels will drop to around 5000 feet
overnight tonight and Winter Storm Warnings and Winter Weather
Advisories are in effect through Friday night for most of the
higher terrain in our region. See the latest Winter Weather
Message (RNOWSWVEF) for additional details.

The next Pacific system, currently located south of the Aleutian
Islands near 40N/170W, is forecast to follow a similar track with
similar impacts. The trough is forecast to dive into southern
California and southern Nevada Friday and Friday night but
precipitation ahead of it will spread into the southern Sierra early
Friday morning and quickly across the rest of the region Friday
afternoon through Friday evening. The latest Model QPF depictions
and GEFS QPF plumes are fairly similar with amounts from each storm.
Average amounts of 0.25-0.50" should be fairly common across the
desert zones although amounts in central and southern Mohave county
should be more in the 0.50-0.75" range. Snow amounts may be a little
higher with the Friday system and accumulations of 1-3 inches may
impact I-15 near Mountain Pass and I-40 east of Kingman Friday
afternoon and evening.

.LONG TERM...Saturday through Wednesday.

2nd system in the parade of storms will be exiting the area Saturday
with shortwave ridging bringing a break in precipitation to most of
the area by afternoon. The only except would be northwest Arizona
where precipitation may linger through Saturday afternoon. The break
will be short-lived as precipitation with the 3rd system looks to
develop in California late Saturday evening and spread across the
rest of the area Sunday. This 3rd system has the potential of
producing more precipitation then the first two combined. However,
there are some large differences between the operational GFS and
operational ECMWF in QPF fields Sunday night-Monday. For now taking
a wait and see approach so made very little change to the Sunday
night-Monday periods.

High pressure building over the Great Basin beyond Tuesday will lead
to dry weather and a period of north winds. 

Temperatures will be below normal during the period.

.AVIATION...For McCarran...East wind at 5-10 kts shifting to the
southwest early this evening. Winds look to become gusty late this
evening as precipitation starts to develop. Precipitation and lower
CIGs to around 5k feet between 05z-15z. Lower CIGs expected to
improve Thursday afternoon. Additional storm system will impact the
region into early next week with precipitation and lower CIGS.
For the rest of southern Nevada...northwest Arizona...and southeast
California...Precipitation and rapidly lowering CIGs to 5-10k feet
are expected to push west across the region this evening. South or
West wind may becoming gusty with the onset of precipitation.
Precipitation and low CIGs are expected to persist through much of
Thursday morning before improving during the afternoon. Additional
storm system will impact the region into early next week with
precipitation/lower CIGS.

.SPOTTER INFORMATION STATEMENT...Spotter activation is not expected
today. A series of storm systems will impact the region tonight
through early next week. Spotters are encouraged to report rain and
snow amounts as well as any weather-related impacts/damage.


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

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