Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 171841

Area Forecast Discussion
National Weather Service Las Vegas NV
1040 AM PST Sun Feb 17 2019

.SYNOPSIS...An abnormally cold weather pattern will persist over our
region through the coming week. This will allow cold low pressure
systems to drop out of Western Canada and bring chances for snow
down to the desert floors. The first system will arrive today into
Monday, and a potentially colder and more vigorous storm could
impact the region Thursday and Friday.

.UPDATE...A fairly tranquil and mostly sunny start to the day
across much of the Mojave Desert Region is still expected to
deteriorate this afternoon and evening. Satellite loops and 12Z
models showed a vorticity lobe sliding over Central California with
its sights set on far Southern Nevada by this evening. The vorticity
advection will provide increased upward forcing over the area from
Clark County southward to I-40 in conjunction with increasing
instability as colder air in the H7-H5 layer moves overhead. This
will support the expected scattered to numerous showers with snow
levels lowering to between 2000 and 2500 feet MSL this evening. The
latest 3-4 runs of the HRRR and blend of convective allowing models
(CAMs) are depicting a focus of showers directly over Clark County
between early this evening and midnight as the cold front and an
embedded closed circulation aloft coincide. If this mesoscale setup
comes together as would be favorable for at least a
few hours of sustained showers with the majority of the Las Vegas
Valley seeing some snow. Although this scenario is not a certainty,
PoP/WX grids will be increased to indicate more extensive shower
coverage, including snow showers, for the majority of the Las Vegas
Valley this evening.


.SHORT TERM...through Monday night. Very cold low pressure moving
into northern CA this morning will be enhanced by a second wave
accelerating southward down the OR coast, resulting in a deep cold
trough being carved out over the southwestern US this evening. This
will bring abnormally low elevation snow to the deserts, with the
best chances this afternoon and evening. Although amounts will
likely be light, significant travel problems could occur with heavy
Sunday traffic between Las Vegas and the Los Angeles area, as well
as traffic on Interstate 40 east of Kingman, so the Winter Weather
Advisory looks good. Winds were just under Advisory criteria in
Barstow and Twentynine Palms early this morning, and will continue
to gust through the day, so the Wind Advisory also looks good.
Precip chances will taper off from west to east tonight through
Monday, with dry conditions expected nearly areawide by Monday
night. The only exception could be lingering snow showers in the
higher terrain of northern and eastern Mohave county. Temperatures
will be several degrees colder today than yesterday, with little
change expected from today to Monday.

.LONG TERM...Tuesday through Saturday.

The main concern in the long term continues to revolve around the
Wednesday night through Friday system. Not much has changed in the
models from the previous runs, with a potent system dropping in from
the Pacific NW expected to bring a decent shot for precipitation
across much of the area. The better moisture will be over the
southern half of the forecast area, so this will be where the most
impacts will be, though high elevation snow is also a concern. Given
the continued model consistency with this system, increased
precipitation chances through the period. The cold low will be
overhead on Thursday, so convective elements are possible with the
precipitation during the day. Also with cold air in place, low
elevation snow will be a concern. The overall setup of this system
progression will be very similar to the one going through today and
tonight, only with a bit extra moisture and a bit colder air. It
will be interesting to see how today pans out as it could be an
indication of how the next midweek system will develop.

As mentioned before, it will be cold through much of the week with
temperatures running 10 to 15 degrees below normal. Record lows or
record low high temperatures are possible, especially Tuesday
through Thursday. By the end of the week, midlevel temperatures warm
slightly but no major warm up is forecast in the near future.

Longer range models still show the back side of the trough shifting
east on Friday then lifting out for the weekend, with more zonal
flow setting up over the southwest deserts. Will continue to watch
to see if this potential pattern change comes to fruitation and we
get a break from this active weather.

.AVIATION...For McCarran...Light and variable winds should become
south to southwest this afternoon. The main concern will be timing
of showers and lower ceilings this afternoon and overnight. Showers
are expected to develop after 20Z in Clark County with isolated
showers possible in the vicinity of the airfield. It is looking
better for prevailing showers this evening with timing of onset
after 03Z, lasting through about 08Z. Cloud decks down to 5k feet
still looks good with the precipitation with low confidence clouds
down to around 030 especially if we see a rain/snow mix. Dry
conditions expected Monday with BKN CIGS between 7-9k feet. Winds
mid morning through the afternoon hours on Monday will be from the
northwest 10-12 knots with gusts up to 20 knots.

For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered showers across much of the region this
afternoon through tonight with CIGS down to 4-6k feet in shower
activity. Winds will generally follow diurnal patterns, except in
DAG where westerly winds will gusts to 30 kts through at least the
evening hours. Gusty northwest winds are expected across much of
the region on Monday.

.SPOTTER INFORMATION STATEMENT...Scattered to numerous snow showers
will occur today and tonight across the Mojave Desert. Spotters are
encouraged to report any significant weather or impacts according to
standard operating procedures.



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