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Area forecast discussion 
National Weather Service Las Vegas Nevada
600 PM PDT Thursday Jul 31 2014

Synopsis...isolated to scattered thunderstorms over east central
Nevada and northwest Arizona will gradually dissipate this evening.
Thunderstorms will be more isolated over the region under a slightly
drier and more stable air mass Friday. Another push of moisture and
an upper level disturbance are expected to spread up across the
region over the weekend for an upswing in showers and thunderstorms.
&&

Update...isolated to scattered thunderstorms were continuing pretty
much where forecast for the evening...mainly along the Sierra and in
Lincoln and Mohave counties. Fairly extensive band of high clouds
across the southeast part of the forecast area has a bit more
opaqueness than forecast. Same story with high clouds blowing off
thunderstorm tops along the Sierra crest toward the northeast. I
updated sky grids for tonight accordingly. -Harrison-
&&

Previous discussion...
320 PM PDT Thursday Jul 31 2014

Short term...through Saturday night...the main area for
thunderstorms through this evening will be Lincoln and Mohave
counties. Thunderstorms were igniting over east central Nevada aided
by a circulation moving into western Utah and also a jet streak
oriented over Utah and eastern Nevada. High res models continue to
show storms expanding in coverage over northern and central Lincoln
County and pushing to the southeast during the late afternoon and
evening. This could lead to thunderstorms brushing the Sheep
Range...northeast Clark and northern Mohave County this evening.
Storm coverage was becoming fairly extensive over the Arizona rim
country and some high res models indicate storms will backbuild
toward southeast Mohave County. Cloud development was slow to build
over the southern Sierra but we could still see a few showers and
thunderstorms fire up as the day progresses. Dewpoints have been
dropping into the low 40s across much of the area. Convection should
diminish during the late evening and overnight. Friday looks to
bring fewer thunderstorms but still the possibility of storms over
the southern Sierra...central Nevada and Mohave County Arizona.

As we go into Friday night and Saturday...attention will be turned
toward the south as a circulation currently over southern Baja California is
forecast to lift up toward northern Baja California and far Southern California
Saturday then head into southern Nevada Saturday night. This will be
accompanied by a significant increase in moisture and I would expect
the leading edge of the circulation to provide some forcing for
overnight shower and thunderstorm development Saturday night. The
latest models were in fairly good agreement with the track and
timing of these features and no significant changes were made to the
going pop/weather and temperature trends.

Long term...Sunday through Wednesday...models are in decent
agreement that a disturbance will move north from Arizona/northern
Mexico Saturday and Saturday night. As this feature pushes north
Sunday through Monday night it should provide ample forcing in a
moisture-rich environment [850-500mb mixing ratios of 6-9 g/kg
across all but the far western areas] to produce at least at least
scattered showers and thunderstorms across the region. With the
added dynamics storms may continue through the overnight hours. The
question will be just how much instability will develop each day and
therefore how much thunder there will actually be...this is often
the big question with these systems. Both the latest GFS and European model (ecmwf)
indicate a punch of drier air over the eastern County Warning Area above 500mb by
Sunday afternoon which may produce enough clearing to allow for some
significant instability to develop. The GFS is not at all
enthusiastic about developing instability in this area while the
European model (ecmwf) is more agreeable and was leaned on more heavily. Less cloud
cover is forecast for Monday...but moisture will also be decreasing.
For the moment have indicated higher probability of precipitation for Sunday. Isolated
pockets of enhanced shear [mainly sunday] could set the stage for a
few organized storms...but with the high moisture content the most
significant threat will be flash flooding both days...especially in
areas with very slow storm motion. Unfortunately it's too early to
have much confidence in exactly where these areas will be.

For Tuesday and beyond expect shower/thunderstorm chances to become
increasingly limited to the far northern areas as moisture slowly
pushes north into central Nevada. Temperatures should rise from 5-10
degrees below normal Sunday back towards normal by mid-week.
&&

Aviation...for McCarran...southwest winds through much of the
evening may give way to northeast winds pushing down from Lincoln
County toward midnight. Isolated thunderstorms in the Peach Springs
and Mormon Mesa corridors should dissipate by late evening. A more
southeasterly wind component is forecast to develop late Friday
morning and afternoon which may favor runway config 4.

For the rest of southern Nevada...northwest Arizona...and southeast
California...isolated to scattered thunderstorms over east central
Nevada...northwest Arizona and the southern Sierra will gradually
dissipate this evening. Fewer thunderstorms are expected across the
region Friday. Scattered-broken bases around 12-15 kft mean sea level. Diurnal winds
generally less than 15 kts can be expected away from thunderstorm
influences.
&&

Spotter information statement...spotter activation is not expected
at this time. However...spotters are encouraged to report any
significant weather conditions according to Standard operating
procedures.
&&

Short term/aviation...Adair
long term...Wolcott

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