Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 201650

Area Forecast Discussion
National Weather Service Las Vegas NV
850 AM PST Wed Feb 20 2019

.SYNOPSIS...A potent low pressure system will dive down from the
north through Thursday, brining cold air, gusty winds, significant
snows for some, and even low elevation snows for others.

.UPDATE...Mid and high clouds are streaming in already this morning
ahead of our incoming winter storm set to impact the region tonight
and tomorrow. Webcams indicate snow already has begun falling near
Ely and across White Pine county, and this activity will spread into
Lincoln county by late this morning.

Overall, the forecast remains on track, although after a cold
morning with clouds streaming in after sunrise, concerned that cold
air will be trapped in some of the valleys limiting the high
temperature by a few degrees. As such, I`ll be shaving a couple
degrees from the temperature forecast for this afternoon.  Will be
sifting over 12z model guidance this morning, but there remains a
wide range of possibilities for snow across the Las Vegas valley and
lower deserts of the Mojave. Will likely maintain a conservative
approach, but locally heavy values will be possible where more
concentrated snow bands develop tonight into Thursday morning.



.SHORT TERM...through Friday.

Winter storm still remains on track, with few, relatively minor
adjustments. The weather maker currently on its way, digging down
into northern California/Nevada. The front edge of the trough will
continue digging south and clear southern Nevada by this evening,
with the rest of the trough following suit, leading to a closed
low by Thursday morning. The low will sit overhead all of Thursday
into Friday before being kicked out of the region on Friday.
Precipitation chances still look to spread from north to south
later this afternoon and evening, with peak activity from Thursday
morning through Thursday afternoon. The best, heaviest activity
still looks to impact Lincoln and Mohave counties, with more
scattered showers or small segments of showers for the rest of the
region. This makes the forecast difficult, as resolving these
smaller features is nearly impossible, let alone where they will
end up.

Snow levels still look to fall to 2500`-3000`, leading to most
places outside of the Colorado River Valley at least seeing snow
fall, if not accumulate. Lincoln and Mohave counties as well as
the Spring Mountains and Sheep Range all have a shot at seeing a
foot or more on the higher elevations, with widespread 4-8 inches
even at the lower elevations in those locations. Just about every
regional highway will be impacted in some way. Snow levels remain
low enough for precipitation to fall in the Morongo Basin as snow,
with the GFS continuing to indicate a band roughly near/along
SR-62. This added enough confidence to include them in the Winter
Weather Advisory, as the area is likely to have the opportunity to
pick up a quick couple inches during this event.

The operational GFS has been the lowest member in its own
ensemble QPF, especially for Las Vegas. The past number of 00Z
runs display this trend, with the ensemble mean about double the
operational value. Given the last event exceeded the operational
run, suspect our QPF grids might be a bit underdone again, but
this likely goes back to the convective mode of the precipitation
and difficulty with pinpoint where showers and bands may set up.
The convection with this system looks to be stronger than that of
the previous system, with the colder air and additional moisture
leading to more instability, comparatively. The stronger
convection may have the added benefit of keeping snow levels from
rising much during the day on Thursday.

By Friday, the system exits the region to the east, with rising
heights and temps in its wake for the weekend.

.LONG TERM...Saturday through Tuesday.

The medium range models indicate the weather pattern remains
progressive through the weekend and early next week with at least an
additional cold trough dropping over the Great Basin and brushing
Southern Nevada and Northwest Arizona. Impacts do not look to be
significant with mainly gusty northwest winds and some scattered
snow showers over the Southern Great Basin zones. High temperatures
should manage to climb back into the 50s in Las Vegas but will
still be 5-8 degrees below normal early next week.

.AVIATION...For McCarran...After a quiet morning, ceilings around
8000 feet will arrive about noon, along with south winds gusting to
20 knots. Clouds will lower further by late afternoon, with chances
for rain and snow beginning around sunset. Lower ceilings and
chances for precipitation will persist through Thursday night before
northwest winds bring in drier air Friday.

For the rest of southern Nevada, northwest Arizona and southeast
California...A cold storm system will bring chances for snow, with
rain limited to the lowest elevations, beginning in the Sierra and
southern Great Basin this morning and spreading across the Mojave
Desert this afternoon and tonight. Widespread low ceilings and
terrain obscuration can be expected, with poor conditions persisting
through Thursday night. Strong westerly winds will also be a concern
today in the Barstow and Morongo Basin areas.

.SPOTTER INFORMATION STATEMENT...Another cold winter storm will
impact the region through Thursday. Spotters are encouraged to
report snow amounts and impacts to roads according to standard
operating procedures.


LONG TERM....Adair

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