High Wind in Arizona, December 14, 2021

Area Forecast Discussion
National Weather Service Las Vegas NV
416 PM PST Tue Dec 14 2021

.SYNOPSIS...Widespread precipitation and gusty winds expected today
as a strong storm moves through the Desert Southwest. Elevations
above 5000 feet will receive precipitation in the form of snow,
while the valleys can expect wetting rains. Gusty south winds will
peak this afternoon, but will ease substantially after sunset. Cool
temperatures will persist through the weekend with dry conditions
expected.
&&

.UPDATE...Quick info on what we have been seeing the past couple of
hours across the region:

[RAINFALL]: An large swatch of precipitation over San Bernardino,
Clark, and Lincoln counties has been enhancing over the past few
hours, likely in response to deepening trough and vorticity lobe
swinging into the region. Moderate to heavy precipitation has been
reported at times with this band with even a few isolated lightning
strikes in in southeast Inyo and Clark counties, likely due to the
intense upward motion near the best vorticity advection. Low
visibilities and minor flooding impacts have also been noted,
especially in San Bernardino where higher radar returns and
continuous rain have been plaguing the region through much of the
afternoon. Overall, areas along and northwest of the I-15 corridor
have seen at least 0.25 to 0.50 inches of precipitation in the past
6 hours.

[SNOW]: Snow has been falling much of the day in the Sierra with at
least 1 to 2 feet in the high terrain over 8000ft, though snow rates
has been tapering off per local webcams and SNOTEL reports over the
past few hours. Further east, snow has started to fall in the Spring
and Sheep Range, with snow levels so far sitting around 7000ft. A
couple inches of snow have been noted on Spring Mountain webcams.

[WINDS] A decent 850mb jet was winds over 50 MPH over southern Clark
and southern Mohave county has allowed for occasional gusts over
60MPH at times, especially ahead of the main band of precipitation.
Elsewhere, widespread gusts 40-50MPH have been reported, though when
precipitation picked up winds tended to diminish slightly.

[Expectation the rest of the night]: With pretty much saturated low
levels and decent PWATs noted over much of the region, expect
moderate to heavy precipitation to continue through the evening.
High-res models show the main band of precipitation containing to
blossom and shift eastward over the next 3 to 6 hours as the strong
upper level trough moves inland. For Inyo and Esmerelda County,
impactful weather should nearing an end with only an hour of two
more of impactful rain, winds, and high elevation snow expected.
Allowed the winter storm warning to continue for the Sierra and
White Mountains though as additional snowfall over 6 inches and
gusty winds over 50 MPH should continue for a few more hours.

Elsewhere, the forecast looks to be mainly on track, with the worst
impacts expected with the main precipitation band as it moves
eastward. Also of note, snow levels will drop back down to 4000 to
5000 feet in the next hour or two. This could cause travel issues in
spots on top of the rain and wind travel impacts, including around
Mountain Pass on I-15, Highway 93 north of Caliente, and I-40 in
Mohave County later tonight.

Precipitation should end quickly behind trough axis and main area of
forcing as the precipitation band marches east this evening. Hi-res
models do want to develop a post frontal band of precipitation
behind the main precipitation shield that would move through Clark,
Lincoln and Mohave County early tonight. This should be lower impact
than the first round of precipitation, but may bring another few
tenths of precipitation and/or another inch of two of snow to areas.
Precipitation will be short lived with this band.

Winds will continue to be breezy through at least the first part of
the night. STrongest winds will be just along the the main frontal
band with the 850mb jet, which should also shift east with the
entire system. The high wind warning and wind advisories look to be
in good shape for now, though will need to watch trends through the
evening to see if winds diminish faster than expected or if the
second band of precipitation will keep winds breezy through
Wednesday early morning.
&&

.PREVIOUS DISCUSSION...1252 PM PST Tue Dec 14 2021
.DISCUSSION...through next Tuesday.

Getting the forecast out early today with an active afternoon and
evening expected. Overall, the forecast remains on track with a
potent rainband expected to push from west to east through the
afternoon and evening hours. Light rain has already begun to spill
into the Western Mojave Desert with light rain reported in
Daggett, with light radar returns on the increase across Lincoln
and western Clark counties are well. Expecting the weather to
continue to deteriorate through the remainder of the day, with
wet conditions encompassing the I-15 corridor by early afternoon.

High resolution models continue to suggest a narrow cold frontal
rainband (NCFR) forming across central/eastern Clark county and
pushing into Mohave county late this afternoon. This NCFR may
contain locally heavy rain rates exceeding 0.5" per hour as well
as embedded thunder and strong wind. Behind this feature, snow
levels will fall dramatically with snow intensity increasing in
the Spring Mountains with rates of 2-3" per hour expected through
the evening. Still anticipating 8-12 inch snow totals in Lee and
Kyle Canyon by late tonight. With the falling snow levels, a quick
burst of snowfall is possible this evening in Mountain Springs
and Mountain Pass as well which will impact Highway 160 between
Las Vegas and Pahrump, and Primm and Baker, respectively.

Back in the lowlands, moderate to locally heavy rain this evening
will make for wet and slick roadways and increased accident rates.
Heavy rainfall in the Flag burn scar may cause excessive runoff
and flooding issues, and have issued a small Flash Flood Watch for
this area to account for the potential risk.

Finally, winds have already begun ramping up with 50 mph gusts
observed across the Southeast Vegas Valley and sporadically
across northwest Arizona. Anticipating these winds to continue to
increase through the evening and persist overnight aided by a
strong southerly low level wind maxima exceeding 60 knots at 850mb
up the Colorado River Valley. With the potential for downward
momentum transport with the heavy precipitation band, as well as
subsidence behind the wave this evening, went ahead upgraded the
wind advisory to a High Wind Warning for central/southern Mohave
county as well as southern Clark county including Lake Mead and
Lake Mohave. 60 mph gusts or greater are likely. Elsewhere, wind
advisory remains effective for much of the Mojave Desert and has
been extended through the overnight hours.

Improving conditions are in store for Wednesday with much lighter
winds and drier conditions as high pressure builds in behind the
trough. Another weak shortwave will clip through the Great Basin
on Thursday, which will mainly work to reinforce the cooler air
across the region and may spark a few high terrain showers in the
Sierra and southern Great Basin. Thereafter, high pressure ridge
will build over the weekend with dry and cool conditions
expected. Overnight lows may get exceptionally cold across the
mountain valleys of the southern Great Basin with fresh snow
cover. Looking ahead to next week, the general pattern is expected
to remain active with another trough developing off the Pacific
coast, however - the impact that it brings to the desert southwest
remains to seen as model variance is still fairly high.

&&

.AVIATION...For McCarran...Strong southerly 35-40 knot wind gusts
will continue through the afternoon and into the evening before they
shift to a more southwesterly direction. Gusts to near 50 knots are
possible around 00z. In addition to strong winds, low ceilings, rain
showers, and reduced visibility will also impact the terminal area
this afternoon and evening. As the precipitation associated with
this Pacific system moves into the area over the next couple of
hours, ceilings will drop to around 2-5 kft with moderate-to-heavy
rain showers moving through between 21Z and 02Z Wednesday. Rain
showers should clear out of the area by 05Z on Wednesday, with gusty
winds and mid-to-low clouds remaining through late Wednesday
morning/early Wednesday afternoon.

For the rest of southern Nevada, northwest Arizona and southeast
California...A Pacific storm will move across the region today and
this evening bringing widespread low ceilings and mountain
obscuration along with strong southwest winds gusting 30-40 kts and
moderate to severe turbulence. Low level wind shear also a
possibility but not confident to include in terminal forecasts at
this time. Light rain, ceilings below 3 kft AGL, mountains
obscurations, and visibilities 3-5SM will continue in the Owens
Valley through early afternoon. Light snow could mix down to the
valley floor this afternoon but not expecting much accumulation at
KBIH. Otherwise, lowering ceilings with mountain obscurations, light
to occasional moderate rain and visibility 3-5SM possible across the
remainder of the terminal sites this afternoon. Ceiling and
visibility conditions will improve this evening as the storm quickly
moves away to the east. However, gusty westerly winds are expected
to continue overnight.

&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to
report any significant weather or impacts according to standard
operating procedures. Snow amounts, high wind gusts, or rainfall
totals exceeding 1 inch are appreciated.

&&

UPDATE...Nickerson
DISCUSSION...Outler
AVIATION...Stessman

For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
411 PM PST TUE DEC 14 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0345 PM     HEAVY RAIN       3 NNE MORONGO VALLEY    34.09N 116.56W
12/14/2021  M1.98 INCH       SAN BERNARDINO     CA   TRAINED SPOTTER

            REPORTED RAINFALL ACCUMULATION FROM 7AM TO
            245 PM.

0345 PM     HEAVY SNOW       ASPENDELL               37.24N 118.60W
12/14/2021  M28.0 INCH       INYO               CA   TRAINED SPOTTER

            SNOW ACCUMULATED BETWEEN DECEMBER 13 AT 1230
            PM AND DECEMBER 14 AT 1500.

&&