Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 192123

Area Forecast Discussion
National Weather Service Las Vegas NV
223 PM PDT Sat Aug 19 2017

.SYNOPSIS...An area of low pressure off the southern California
coast will pull moisture northward into the region Sunday afternoon
and overnight, resulting in rain showers and scattered thunderstorms
Sunday night into Monday. Daily thunderstorm chances will persist
through midweek before conditions gradually dry out late in the week.

.SHORT TERM...through Tuesday night.

Scattered thunderstorms all north of our forecast area this
afternoon. Storms running from Mono County east toward Ely. We still
may see some showers or a brief thunderstorm late this
afternoon/early evening in northern Inyo and Esmeralda County.
Remainder of the area will be dry with seasonable temperatures

Our extended break from moisture and thunderstorm chances will come
to an end Sunday, then extend into mid-week. A southerly flow ahead
of a quasi-stationary upper low off the southern California will
help pull moisture from the lower Colorado River/southwest Arizona
northward into Mohave, Clark and eastern San Bernardino County
tonight and Sunday. Modest instability along with increasing
diffluence aloft associated with left exit region of H25 jet should
help ignite scattered thunderstorms over the higher terrain of
Mohave County with coverage more isolated west of the Colorado River
in eastern San Bernardino and Clark County Sunday afternoon.
Anticipate coverage in showers and thunderstorms to explode Sunday
night into Monday morning as that period coincides with period of
strongest jet dynamics and bulk shear (20-30 Kts) to help develop
pockets of more organized convection. As for the solar eclipse.
Timing could not be any worse for much of the region. There may be
parts of the western Mojave Desert with less cloud cover but breaks
more be more difficult to find in northwest Arizona and southern
Nevada Monday morning. On Tuesday, mid-levels dry out while low
levels remain moderately moist. Surface heating and proximity of
nearby jet should aid in another day of isolated/scattered
thunderstorms. Threat from the thunderstorms includes gusty winds,
heavy rain and hail. Precipitable water values not outrages as
compared to climatology for this time of August. Will need to
monitor for area of cell training that could produce localizes flash
flooding Sunday night/Monday.

Temperatures will fall to below normal under increasing
cloud/precipitation chances.

.LONG TERM..Wednesday through Friday.

A weak closed low spinning off the SoCal coast will make eastward
progress Wednesday and will become more of an open wave as it tracks
inland. There is some disagreement between the GFS and ECMWF
solutions, wherein the GFS wants to keep a shallow moist layer over
the region and move the upper trough a tad quicker than the much
drier ECMWF. Leaning toward the GFS solution here (i.e keeping
moisture and weak dynamic lift over the region) and have left slight
chance PoPs in lower elevations and chances in the mountains on
Wednesday. Given slow progression of this trough and residual
moisture, there may be enough dynamic lift to keep showers and
thunderstorms going through the late evening Wednesday, therefore I
have increased PoPs to slight over Mohave County late
Wednesday/early Thursday. Dry westerly flow will push in behind the
trough on Thursday and will advect moisture eastward and dry out
most areas. The exception will be eastern Mohave and Lincoln
Counties where minimal moisture and limited instability will remain
through the afternoon Thursday. This may yield some isolated shower
and thunderstorm activity across NW Arizona. By Friday, dry and
clear conditions are expected across all southern Great Basin and
Mojave Desert zones. Temperatures will start off a few degrees below
normal Wednesday and will trend up to mid-August normals by Friday.

.AVIATION...For McCarran...East-southeast wind primarily
under 10 kts through early evening. Typical diurnal pattern
overnight through Sunday morning. South wind will develop Sunday
afternoon with periodic gusts up to 20 kts possible. Mostly clear
overnight with clouds between 10-15 kft increasing through the day
Sunday. There is a slight chance for an afternoon thunderstorm
Sunday over the higher terrain west and south of Las Vegas. Better
chances for showers and thunderstorms exists for the terminal Sunday

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. Additional moisture will lead to a slightly better chance of
showers and thunderstorms over the higher terrain of northwest
Arizona and the Mojave Desert Sunday afternoon.

.FIRE WEATHER...Better chances for storm activity arrive
Sunday afternoon and increase Sunday night into Monday 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 Bernardino 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 afternoon 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...Pierce
Long Term...Boothe

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