Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 201650

Area Forecast Discussion
National Weather Service Las Vegas NV
950 AM PDT Thu Jul 20 2017

A slight drying trend is expected through the weekend with a
majority of the shower and storm activity confined to Mohave and
eastern Lincoln counties each day as well as the higher
elevations of Clark County. Temperatures will warm back up to
around seasonal normals approaching the weekend.

.UPDATE...Split and tweaked PoP grids with latest CAM guidance,
and accompanying sky, qpf, and weather elements as well. In
general, a lot less activity today despite relatively impressive
CAPE profiles. Most guidance confines activity to small portions
of Mohave and Lincoln counties, though a thunderstorm or two
cannot be ruled out on higher terrain in Clark and eastern San
Bernardino counties. The high is forecast to begin shifting and
veering flow over the area, commencing a drying trend from west to
east today.

.AVIATION...For McCarran...Winds will favor a southeast direction
with speeds under 10 knots through early this afternoon with winds
then becoming southerly around 10 knots. Winds this evening and
overnight will generally be from the southwest up to 10 knots. SCT
to BKN mid to high clouds will be present for the period. Showers
and storms developing across the higher elevations around the valley
this afternoon and evening could create brief gusty, erratic winds
at the terminal but confidence in that happening is low.

For the rest of southern Nevada, northwest Arizona and southeast
California...Prevailing south to southwesterly flow can be expected
across the region today as high pressure remains centered to the
east with varying degrees of mid/high cloud coverage remaining over
the area. Winds could become gusty along the Colorado Valley today
with gusts up to around 25 knots possible at times. Isolated to
scattered showers and storms will be possible once again today;
primarily across Mohave, eastern Lincoln, and the higher elevations
of Clark County this afternoon and evening.

.PREV DISCUSSION... /issued at 359 AM PDT Thu Jul 20 2017/

.SHORT TERM...Today and Friday.

Deep layer moisture remains in place across Lincoln, eastern Clark,
eastern San Bernardino, and Mohave counties today with PWAT
values still in the 1.0-1.5 inch range. As instability increases
into the afternoon, with the help of diurnal heating, isolated to
scattered showers and storms are expected to develop with highest
coverage across Mohave and eastern Lincoln counties. Best chances
for Clark County will be across the higher elevations this
afternoon and evening. Even though the airmass itself has not
changed significantly since yesterday we have decided to not go
with a Flash Flood Watch for any portion of the area today as
there is a lack of any outside trigger or forcing mechanism to
help create widespread, severe impacts like we saw yesterday with
the midlevel circulations that progressed through Mohave and Clark
counties. Yesterday`s circulation should make its way up into
southwest Utah today where a higher threat of flash flooding
exists, leaving us on the subsident side of things which could
further inhibit larger coverage of convection. However, this
doesn`t mean that some of the afternoon storms today could not
become strong to severe with locally heavy downpours but with
these larger scale factors not present widespread impacts are not
expected at this time. Mid and high cloud coverage should hold off
temps slightly below normal this afternoon with prevailing south
to southwest flow. Only other update to the forecast for today was
to include patchy smoke across Esmeralda and northern Inyo
counties as a large fire is burning just to the north in Mariposa
County California and there will be potential for smoke to spread
southward across these areas today and tonight.

On Friday the center of the ridge pushes further east allowing
for slight drying as moisture axis also shifts eastward. Best
coverage of showers and storms on Friday will be across the
Arizona Strip which is expected to remain scattered at best.
Isolated activity across the higher elevations will be possible
once again in Clark and Lincoln counties. Warming trend begins
Friday with more sun and drier airmass allowing temps to come back
up to seasonal norms.

.LONG TERM...Saturday through Thursday.

The potential for isolated thunderstorms around southern Nevada and
northwest Arizona will not be completely eliminated Saturday and
Sunday as sufficient moisture and instability should remain for a
slight chance over the mountains. The door for monsoonal flow then
opens wide Monday and Tuesday as high pressure over Nevada during
the weekend heads over the Four Corners allowing southeast to
southerly flow to draw additional moisture into most of our region.
It appears sufficient moisture will be pulled far enough westward
for a chance of thunderstorms over the Sierra, especially Monday
into Tuesday. The ECMWF and GFS indicate a broad trough approaching
the West Coast Wednesday into Thursday which would lead to dry
southwest flow working into our region. The GFS indicates more of a
drying trend than the ECMWF. The gridded forecast reflects a slight
downward trend in thunderstorm potential Wednesday into Thursday
based on the GFS. Temperatures will remain near normal though
significant variations could occur due to showers and thunderstorms
for any given location.

Monsoonal moisture will remain in place over Mohave, Clark,
Lincoln, and eastern San Bernardino counties today and tomorrow
before shifting eastward has high pressure pushes away from the
region. Chances for showers and storms will continue for the
aforementioned areas today and tomorrow; becoming more isolated
and confined to just Mohave County for the weekend. Heavy
rainfall, gusty winds, and lightning will be possible with these
storms. Drier air remains over Inyo, Nye, Esmeralda, and western
San Bernardino counties with no significant widespread wind
events expected through early next week.

Creeks, streams and rivers in northern Inyo County
continue to run high and fast from snow melt. Some road closures
continue in the area. Bishop Creek Bypass and Big Pine Creek Bypass
continue to be utilized to minimize flows through Bishop and Big
Pine. Remember, never drive through flooded roadways or around
barricades. Also, pastureland or farmland adjacent to creeks,
streams or rivers could experience areas of standing water.

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



LONG TERM....Adair

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