Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 250929
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
229 AM PDT MON JUL 25 2016

.SYNOPSIS...Hot and dry conditions to start the week will give way
to increasing thunderstorm chances by Tuesday. Another push of
monsoonal moisture looks to impact the region for the upcoming
weekend as well.
&&

.SHORT TERM...through Wednesday night.

The main forecast concerns for the short term continue to be smoke,
heat, moisture return/thunderstorm chances. Moisture continues to
seep up the Colorado River Valley, though remains too shallow to
produce any convection or remain established away from the river
valley. A shortwave propagating from the Pac NW into the Northern
Rockies will subtly disrupt ridging and nudge it a little eastward.
This hopefully will result in a more southerly shift to transport
winds in the western half of the area, which should help with smoke.
This will also allow an expansion of E/SE flow in southern parts of
the area. This was already evident overnight, with an MCS along the
international border near Tucson, about 50 miles north of last
night`s. This trend is thus expected to continue over the next few
nights, though may be tempered by the ridge regrouping over southern
Utah/northern Arizona by mid week.

Moisture will continue to increase over Mohave County today. The NAM
even indicates a weak jet streak with an axis roughly from Vegas to
Grand Junction. This leaves Mohave county in what right entrance
region dynamics exist. Thus, a slight increase in POPs/coverage is
not unreasonable to expect today. High resolution ensembles continue
to peg the Mogollon Rim and northward into the evening for
thunderstorms.

Tuesday is looking like a much trickier forecast than previously
thought. As the upper level high recovers in the Great Basin, mean
easterly flow expands over the southern portions of the
area...leaving southern Nevada on the periphery. Thunderstorm
activity Tuesday afternoon will be highly dependent on thunderstorms
Monday night, which could easily expand moisture further
northward/westward than expected. Similar concerns are also valid
for Wednesday as well. In any case, a general uptick in
thunderstorms for the southern one-half to two-thirds of the area is
likely, including the McCullough Range and Spring Mountains.

Expect increasing moisture to help combat strengthening high and
keep temperatures rather steady through mid-week, with highs around
110 for the Mojave Desert, and 115 for the Colorado River Valley.
While above average, these temperatures are not close enough to
excessive heat criteria for product issuance. However, the long
string of days with highs around 110 and lows in the upper 80s is
likely to impact more prone groups such as the elderly and homeless.

.LONG TERM...Thursday through Sunday.
Still looks like a transition from very hot and dry to seasonably
hot and stormy during the period. Mid level high pressure over the
Great Basin bakes the region Thursday and Friday, with temperatures
looking just a bit shy of Excessive Heat Warning levels. Also on
Thursday, a tropical wave slides west across the mouth of the Gulf
of California, which is a well documented pattern to trigger a Gulf
Surge. Deeper moisture should arrive in the southern CWA on Friday
and spread areawide over the weekend, bringing increasing chances
for thunderstorms and knocking temperatures down somewhat.
Confidence in this outcome is slowly increasing, as the models have
looked quite similar for three consecutive mornings now. Thus,
increased PoPs a little more. Will continue to monitor.
&&

.FIRE WEATHER...Dry and hot conditions will persist across southeast
California and southern Nevada through Tuesday. Northwest Arizona
should see increasing thunderstorm coverage by Tuesday afternoon as
storms move off the Arizona rim country from northeast to southwest.
It is looking favorable for a widespread return of monsoonal
moisture and associated thunderstorms by next weekend.
&&

.AVIATION...For McCarran...Winds will once again favor typical
diurnal trends through the TAF period. Southwest gusts will develop
once again by the afternoon, with overnight winds varying from 210-
170. Smoke will likely be less of a concern as the day goes on,
shifting west of the Las Vegas valley.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Gusty afternoons will continue for the next few days,
with expanding thunderstorm chances in Arizona. Smoke will remain an
issue in southeast California, with the biggest issues near the
surface expected in the evening, likely remaining aloft during the
day.
&&

.SPOTTER INFORMATION STATEMENT...Spotter activation is not
anticipated today although spotters are encouraged to report any
significant weather...including smoke near the surface/visibility
reductions using standard operating procedures. Spotter activation
may be necessary later this week.
&&

$$

Short Term/Aviation...Steele
Long Term.............Morgan


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