Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 262002

Area Forecast Discussion
National Weather Service Las Vegas NV
102 PM PDT Sun Sep 26 2021

.SYNOPSIS...An upper level disturbance will bring chances for
showers and thunderstorms to far southeast California and northwest
Arizona today, with a few lingering storms possible in far eastern
Mohave County Monday. A fairly significant pattern change is in
store for the upcoming week, with breezy to windy conditions
expected Tuesday, chances for rain mainly north and east of Las
Vegas Tuesday and Wednesday, and a few days of cooler temperatures
for the latter half of the week.

.SHORT TERM...through Monday night. Early afternoon satellite loop
showed thick mid and high level cloud cover over much of Arizona,
with a very complex flow pattern evident. The large scale flow was
cyclonic around the upper low, which was over far northern Sonora,
and smaller scale swirls associated with a vorticity lobe and
mesoscale convective vortices were noted over Arizona. The clouds
were moving west to southwest in the large scale flow and thinning
out as they reached Clark and San Bernardino counties. Convection
was trying to develop over Mohave County, but was being suppressed
by the lack of daytime heating thanks to the cloud cover. As the
afternoon goes on, expect differential heating boundaries to form
under breaks in the clouds, which should help scattered storms pop.
Yesterday and Friday, isolated storms developed farther west than
anticipated. Today, skies are mostly clear and surface dewpoints are
near 50F over Clark and eastern San Bernardino counties, so
increased mountain PoPs a little in these areas. The low will move
slowly east and northeast tonight and Monday, with only a few
wraparound showers or thunderstorms expected Monday in far eastern
Mohave County. By Monday night, the long-advertised pattern change
will begin as a strong trough rolls into the Pacific Northwest. More
on that in the long term and fire weather sections.

.LONG TERM...Tuesday through Saturday.

A fairly strong Pacific trough will edge into the Pacific Northwest
region on Tuesday while dragging a cold front through the Great
Basin and eventually the Mojave Desert Tuesday night into Wednesday.
Ahead of this front, gusty winds and mild conditions can be
expected, with the strongest winds across the favored wind belt from
Barstow northeastward up the I-15 corridor. A few showers may also
form with the front across mainly Lincoln and northern Mohave
Counties. Behind the front, much cooler temperatures will follow
with afternoon highs on Wednesday dropping 5 to 10 degrees below
daily normals.  Ensemble guidance has been trending deeper with some
lingering energy late in the week which closes off and drops into
Arizona by Friday. This will keep our region on the cooler side of
normal through the end of the week, with temperatures only slowly
returning to near normal by the weekend.

.FIRE WEATHER...Models continue to indicate a trough moving
through the Great Basin Tuesday. Jury remains out just how strong
will the winds get and if critical thresholds will be exceeded
across southern Nevada and northwest Arizona. Humidity values still
look to stay above 15 percent across all of Mohave County and much
of Clark and Lincoln Counties. There actually may be more concern
for Esmeralda and Nye Counties as gusty north winds develop behind
the cold front will humidity values potentially lowering to 10-15
percent. Will continue to monitor.

.AVIATION...For McCarran...Light winds near the terminal today
are leading to highly variable wind directions. Expect this won`t
have a great deal of impact on air traffic due to the light speeds.
Nonetheless, expect a general easterly oriented wind to set up in
the afternoon and return again to southwest near sunset. A few mid
and high clouds can be expected through the TAF period as well. The
chances of thunderstorm activity in the Peach Springs corridor is
looking a bit less likely in terms of extent and strength. However,
it is still worth noting that outflow winds from any storms in that
area may affect the terminal in the very late afternoon and evening.
Stay tuned for updates.

For the rest of southern Nevada, northwest Arizona and southeast
California...Relatively light winds following twice-daily trends are
expected at the remaining TAF sites. Smoke is impacting portions of
Inyo County, including KBIH. KBIH specifically is expected to drop
into MVFR conditions around 00z. IFR conditions are not out of the
realm of possibility in the vicinity of KBIH and the rest of the
Owens Valley overnight.

Isolated showers and thunderstorms in the southeastern portion of
CA/NW portion of AZ will result in SCT-BKN clouds with bases above
10 kft at KEED and KIFP for most of the day. These storms may result
in vicinity showers and/or thunderstorms later in the afternoon with
the possibility of outflow winds impacting the terminals.

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


LONG TERM...Outler

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