Area Forecast Discussion
Issued by NWS Las Vegas, NV

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717
FXUS65 KVEF 190902 AAA
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
205 AM PDT Sat Aug 19 2017

.SYNOPSIS...Dry and warm conditions expected today with just some
isolated storm activity across northern Inyo and Esmeralda counties.
A closed low off the California coast will direct increasing
moisture into the region Sunday afternoon and overnight, resulting
in widespread showers and thunderstorms Sunday night into Monday.
Daily thunderstorm chances will persist through midweek before
conditions gradually dry out late in the week.

&&

.SHORT TERM...through Monday night.

Fairly tranquil conditions are expected for the next 24 hours as a
southerly flow aloft develops but atmospheric moisture content
remains low. Only areas of interest will be far northern Inyo and
Esmeralda counties where a few stray showers may develop this
afternoon and evening along the southern edge of a deformation zone
over the Great Basin.

Bigger changes take shape Sunday as a closed low off the SoCal
coastline begins to advect deeper moisture northward. This will set
the stage for some isolated storm development as early as Sunday
afternoon across Mohave county as well as in the Spring Mountains
and Mojave Preserve. By Sunday night, a strong jet rounding the base
of the SoCal low will be entering Western Arizona, along with a
continued feed of deeper moisture moving in. This places areas south
and east of I-15 in a favorable quadrant of the jet for widespread
lift, and will promote nocturnal shower and thunderstorm development
during the early morning hours Monday. Where these bands of showers
and storms set up will be the big question, but somewhere in the
Clark, eastern San Bern, and Mohave county area will be the most
favored.  This activity will tend to lift northward Monday morning,
expanding into the Southern Great Basin and Inyo county by Monday
afternoon. Depending on the amount of cloud cover, additional storms
are likely to flare up Monday afternoon in response to daytime
heating and continued favorable jet dynamics.

Moisture content advertised Monday is not particularly noteworthy
for August, but the dynamics involved with the closed SoCal low may
compensate for the lack of deeper moisture, as this tends to be a
convectively favorable set up for our region. Main concerns will be
training thunderstorms leading to flash flooding, as well as locally
strong thunderstorm wind gusts.

Given the timing of the anticipated shower and thunderstorm
activity, cloud cover will undoubtedly be a concern for Eclipse
spectators. At this point, we`ll need to hope for some breaks in the
clouds to be able to see much across Nye, Clark, Lincoln, and Mohave
counties. Better viewing conditions are likely across Western San
Bernardino County, with more uncertainty across Inyo and Esmeralda
counties.

.LONG TERM...Tuesday through Friday.

The upper low will remain parked just off the southern California
coast Tuesday with southerly flow keeping low grade monsoon moisture
and some instability over much of the forecast area. Not expecting
much change for Wednesday as the low starts to move inland. Kept a
slight chance of thunderstorms over most valley locations both days
with chance pops over the mountains. The exception is a dry forecast
for western and southern San Bernardino County as both the GFS and
ECMWF indicate somewhat drier and more stable air in place there.
The upper low will continue to weaken into an open wave as it moves
into Nevada Thursday. This will bring drier and more stable air into
much of the forecast area. However, there will still be some
moisture and weak instability over Mohave and Lincoln Counties along
with some forcing from the trough so I increased pops in those areas
for a mention of thunderstorms Thursday afternoon. The push of drier
air looks to continue Friday as the trough continues to move slowly
east. For now I kept the dry forecast going for Friday but the ECMWF
is a bit slower with the eastward progression of the trough and
generates some QPF over Mohave and Lincoln Counties. So, we will
have to watch model trends for possible pop increases.

&&

.AVIATION...For McCarran...Light winds favoring diurnal patterns and
mostly sunny skies favored through the TAF period. A period of
southeast winds in the 9-12 knot range with occasional gusts to 16
knots will be possible between 21z-00z before shifting more
southerly in the evening.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds favoring diurnal trends expected through
the period. A few showers and thunderstorms will be possible near
KBIH during the late afternoon and evening before diminishing after
sunset.

&&

.FIRE WEATHER...Generally dry conditions expected Saturday aside
from a few stray showers and storms in Northern Inyo County. Better
chances for storm activity arrive Sunday afternoon and increase
overnight across much of the Mojave Desert and Northwest Arizona,
with widespread clouds and shower activity expected Monday. Showers
and storms will remain possible mainly north and east of San Bern
county Tuesday and Wednesday before gradual drying moves in late in
the week. Temperatures will tend to be near seasonal normals, though
a bit cooler than usual Monday thanks to widespread clouds.



&&

.SPOTTER INFORMATION STATEMENT...Increasing thunderstorm
activity is expected Sunday and into the middle of next week.
Spotters are encouraged to report any significant weather or impacts
according to standard operating procedures. &&

$$

Short Term/Aviation/Fire Weather...Outler
Long Term...Harrison

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