Scientific Forecaster Discussion
fxus65 kvef 202037
Area forecast discussion
National Weather Service Las Vegas Nevada
140 PM PDT Wed Sep 20 2017
Synopsis...blustery conditions Thursday will be followed by sharply
cooler conditions Friday and through the weekend. A few showers are
likely tomorrow across the southern Great Basin and Sierra, with a
dusting of snow likely on the highest Sierra ridgetops. Dry but cool
conditions will linger into early next week.
Short term...through Friday.
A potent early season trough is on the way and will deliver the
first taste of truly Fall-like weather to the region, just in time
for the first day of autumn. But first, we have to get through the
wind. Ahead of this trough, a tight pressure gradient will be
setting up, inducing a swath of southwest winds across the region
with gusts of 40-50 mph expected. The strongest of these winds will
stretch from the western Mojave Desert into Mohave and Lincoln
counties, and will encompass both the I-40 and I-15 travel
corridors. Winds across the western Mojave Desert will start to
pick up as early as this evening, but should stay just shy of
advisory criteria until tomorrow afternoon. With this in mind, have
posted a Wind Advisory from late morning tomorrow through late
Thursday night for much of the region. Further north and west,
strong winds will develop along the eastern Sierra crest as early as
this evening, with wind gusts over to 60 mph possible along the mid
and upper slopes, so I posted a Wind Advisory for that area starting
late this afternoon and continuing through Thursday evening. At this
time, it looks like the strongest winds will stay out of the Owens
Valley with the exception of a very localized burst here or there.
In addition to the wind, a narrow band of showers is likely as the
trough and associated cold front slide into the region tomorrow.
This will mainly impact the southern Great Basin, though its
possible even the Spring Mountains could squeeze out a shower late
in the day.
As the cold front pushes through Thursday evening and overnight,
much cooler air will invade in its wake. High temperatures Friday
will average 12-18 degrees cooler than normal, with morning low
temperatures approaching freezing in the northern Owens Valley near
Bishop, and colder pockets of the southern Great Basin.
Long term...Saturday through Wednesday.
Dry northerly flow will follow the much anticipated cold front just
in time for the first weekend of fall. The main impacts will be the
potential for some isolated freezes Saturday and Sunday mornings.
Areas of concern include higher elevations across the southern Great
Basin and Inyo County where temperatures will be below or near
freezing. Proper precautions regarding pets and sensitive vegetation
should be considered this weekend. As the upper low exits the
southern Great Basin Saturday afternoon, lingering forcing across NE
Lincoln County may trigger some light showers Saturday afternoon.
Elsewhere, expect dry conditions and unseasonably cooler
temperatures through the weekend. Temperatures will increase 1-3
degrees each day under continued broad troughing before subsequent
ridging midweek. Mostly clear skies and breezy north winds can be
expected each afternoon.
Fire weather...breezy conditions this afternoon will be followed by
much stronger winds across much of the area Thursday. Wind gusts may
exceed 40 mph at times along a belt from the western Mojave Desert
into southwest Utah, and also along the Sierra crest. Much cooler
conditions will follow this system with below normal temperatures
expected Friday through early next week. Critical fire weather
conditions are not expected due to relatively high fuel moisture and
marginal forecast humidities.
Aviation...for McCarran...winds are likely to remain elevated
through the overnight hours out of the south or southwest. There may
be brief periods of southeast winds, which are most likely to occur
in the overnight hours. Expect gusty southwest winds to increase
once again tomorrow, with gusts of 30 to 40 knots possible by the
afternoon. Mountain wave activity may produce a few lenticular
clouds, but no operationally significant ceilings anticipated. The
primary hazards will be strong surface winds, turbulence, and
mountain wave activity.
For the rest of southern Nevada, northwest Arizona and southeast
California...winds will be slow to subside this evening, if they do
so at all, especially along the I-15 corridor from dag-las-sgu.
Expect winds to pick up again tomorrow, with gusts in excess of 30
knots expected across most of the area tomorrow. VFR conditions will
prevail, however, expect enhanced winds along with mountain wave and
associated turbulence near mountain ranges through the period,
especially the Sierra Nevada and Spring Mountains.
Spotter information statement...a more fall-like pattern will bring
cooler temperatures and gusty winds over the next week.
While spotter activation is not anticipated, reports of wind
impacts such as blowing dust or damage are appreciated.
Short term/fire weather...outler