Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 302216

Area Forecast Discussion
National Weather Service Las Vegas NV
315 PM PDT SAT JUL 30 2016

.SYNOPSIS...Moist and unstable air will lead to a chance of
thunderstorms across much of the area through Sunday. Southern
California may see a drying trend for the first half of next week
while northwest Arizona and southeast Nevada will keep a chance of
thunderstorms each day.


Near-term/mesoscale discussion...WV imagery indicates a weak
vorticity maximum on the north side of a broad midlevel ridge moving
through eastern Nevada at this time. Convection is already beginning
to initiate near this feature. More storms are developing in the
Spring Mountains with the aid of orographic ascent. Precipitable
waters are at or above one inch across the area with a nose of >1.5
inch values along the Colorado River and adjacent southeast San
Bernardino and southern Mohave Counties. Theta-e ridge extends
northward through Mohave County as well. Morning sounding shows a
sharp increase in moisture (PWs increased from ~1.1 to ~1.4 inches
in 12 hours) in a conditionally unstable environment. The residual
dust from last night`s storms in Arizona have impeded surface
heating to some degree, but as mixing continues this afternoon,
environment will become quite unstable (with high-resolution models
showing >2000 J/kg SBCAPE in eastern portions of the area by this
evening) with minimal convective inhibition.

Expecting isolated to scattered storms to develop in the higher
terrain through the afternoon with some progression into nearby
valleys/deserts possible, especially if outflows can generate enough
lift to overcome increased inhibition in these areas. Outflow
boundary intersections will be especially favorable for renewed
convection. Given degree of instability and large surface dew point
depressions, hail and gusty winds will be possible this afternoon
and early evening.

With deep-layer shear ~30 kts, environment is favorable for some
mesoscale organization. Convection-allowing models have consistently
shown storms developing in eastern Nevada/southern Utah this
afternoon/evening loosely growing upscale into a mesoscale
convective system that progresses SSE through Lincoln, Clark, and
Mohave Counties as 850-mb jet enhances convergence/lift downstream.
With moderately unstable environment and sufficiently high DCAPEs
(1000-2000 J/kg), gusty surface winds are likely along outflows and
the developing cold pool. In addition, the increasingly moist
thermodynamic profile suggests rain rates will become more favorable
for localized flash flooding. A flash flood watch has been issued
for this evening and tonight for portions of Lincoln, Clark, and
Mohave Counties where the greatest risk of storms coincides with the
most favorably moist environment.

Sunday through Tuesday...Mid level high pressure continues to wobble
over the area Sunday...likely becoming centered roughly over San
Bernardino County. Models are showing a little bit of a push of
drier and more stable air into northwest San Bernardino and southern
Nye County but the remainder of the area should remain pretty moist
and fairly unstable with the highest chance of thunderstorms over
the eastern half of the cwa. The models agree on pushing the
somewhat drier and more stable air a bit farther east Monday and
Tuesday with thunderstorm chances mainly over Lincoln, Clark, Mohave
and eastern San Bernardino Counties. This is due to a fairly strong
trough moving into the Pacific Northwest during that time frame.
This will also result in near to slightly below normal temperatures.

.LONG TERM...Tuesday night through Saturday...

Things may get more interesting beginning Tuesday night as the
models are indicating an inverted trough over northwest Mexico
getting pulled north and slowly moving across western Arizona late
Tuesday night through at least Thursday. The models are indicating
very moist and unstable air with this feature, especially over
Mohave County and eastern portions of San Bernardino, Clark and
Lincoln Counties. I increased pops a bit for this period but did not
get too crazy as that is a bit far out to be very confident in the
evolution of that wave. Certainly something to keep a sharp eye on.
For Friday and Saturday, right now it looks like a drying trend may
take place as there is some model agreement in bringing a weak open
trough across the area from west to east. It may not be enough to
totally flush the moisture out of the eastern part of the cwa

.AVIATION...For McCarran...Dust continues to plague the Las Vegas
Valley this afternoon, as stronger SSW winds and associated mixing
have not commenced sufficiently to scour it. Expecting improvement
to occur only gradually through afternoon. Storms have developed in
the nearby higher terrain which may affect flight corridors this
afternoon, with chances for storms increasing this evening/overnight
as a more organized system moves north to south through the area.
Mainly S/SW winds with gusts up to 20 kts expected through tomorrow.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Storms developing this afternoon in the high terrain
may move into adjacent valleys/deserts with gusty/erratic outflow
winds, locally lowered CIGs, and lightning all threats. Outside of
storms, S/SW winds 10-20 kts with gusts to 30 kts likely through
tonight with strongest speeds this afternoon/evening. Chances for
more widespread storms exist tonight in Lincoln, Clark, and Mohave
Counties as a cluster of storms moves north to south through the

.FIRE WEATHER...Much of the area will have a chance of thunderstorms
through Sunday. Gusty winds will be possible but there is also
potential for heavy rain, especially with storms across Lincoln,
Clark, Mohave and eastern San Bernardino Counties. Somewhat drier
and more stable air may push into western San Bernardino and
southern Inyo County Sunday and by Monday and Tuesday possibly
pushing into Esmeralda and Nye Counties as well.

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
significant weather according to standard operating procedures.


Short Term...Shafer/Harrison
Long Term/Fire Weather...Harrison

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