Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 201922

Area Forecast Discussion
National Weather Service Las Vegas NV
1222 PM PDT Tue Oct 20 2020

.SYNOPSIS...Warm and dry conditions will continue for a couple
more days before a gradual cooldown ensues near the end of the
workweek. A pattern change will bring a return of cooler and
blustery conditions over the weekend and lingering into next week,
with chances for rain and mountain snow showers, especially north
of Las Vegas on Sunday.


.SHORT TERM...through Friday.

Dry northwesterly flow will continue for a few more days as deeper
troughing remains focused across the Northern Rockies, and high
pressure persists across the Southwest. Lingering smoke from
ongoing wildfire activity will remain problematic across the Owens
Valley, with lofted smoke continuing to drift eastward across the
Mojave Desert and Southern Great Basin. Heights will be gradually
declining through Friday, with temperatures likely peaking today
or tomorrow before cooling a few degrees both Thursday and Friday.

As mentioned in the previous discussion, tomorrow looks like the
last chance for Las Vegas to reach 90 before cooling off Thursday
and Friday. Odds are good that should we hit 90 tomorrow, it would
be the last 90 degree day of the 2020 calendar year.

.LONG TERM...Saturday through next Tuesday.

A significant change in the weather pattern remains on track for
the longer term period, though details are still coming together.
On Saturday, a strong shortwave will round the base of the
longwave trough and push into the northern Rockies. This will
result in an increasingly tight thermal gradient across the Great
Basin and Mojave Desert, leading to gusty southwesterly winds in
the afternoon. While minimum humidity values look marginal, gusty
winds and dry fuels could result in a period of increased fire
danger for some of the region on Saturday afternoon.

Larger changes take shape on Sunday, though this is around the
timeframe when models diverge on the details. Cluster analysis had
been suggesting most Canadian solutions favoring a deeper and
more westerly trough which would lead to better precip chances
across our region, as well as the largest degree of cooling. While
the ECMWF and GFS have suggested a more progressive, broad
trough, with moderate cooling but fairly limited precipitation
coverage. Of note this afternoon however, is that the ECMWF
guidance has trended sharply more towards the colder and wetter
Canadian ensemble solutions. A little too early to latch on to
this idea with confidence, but it`s good to see the models
trending in a certain direction.

In summary, prepare for a blast of much cooler, fall-like weather
for the upcoming weekend which will last into early next week.
Precipitation chances will be greatest across the Sierra and
Southern Great Basin, but some shower activity may spread into the
lower deserts if the cooler and wetter solutions should come to
fruition. Could our record dry spell be coming to a close? Stay


.AVIATION...For McCarran...Light and diurnal winds will continue
through the majority of the TAF period, with light easterlies
through the morning and afternoon and light southwesterlies after
sunset. Wednesday afternoon, winds are expected to have a similar
pattern, though low confidence in a breezy southwesterly push
between 22 and 23Z around 10 kts reaching the Las Vegas Valley until
after sunset - leaving this out of the prevailing TAF for now. No
operationally significant cloud cover expected through the TAF

For the rest of southern Nevada, northwest Arizona and southeast
California...Light and diurnal winds expected across the region
through the TAF period. Potential mountain obscuration and a
decrease in visibilities due to lingering wildfire smoke will return
along the Owens Valley after sunset, clearing out through the
morning. Visibility may drop down to 3-4 SM at times. Otherwise, no
operationally significant cloud cover expected.


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



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