Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 281006 AAA
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
305 AM PDT THU JUL 28 2016

.SYNOPSIS...Dangerously hot conditions are expected to continue
through the end of the week. Isolated mountain thunderstorm activity
will be possible during the afternoons before becoming more
widespread over the weekend and beyond as monsoon moisture returns
to the area. Increased clouds and moisture will allow temperatures
to cool closer to seasonal normals by the weekend. &&

.SHORT TERM...through Friday night.

Heat remains the big story for the next couple of days, with record
or near record temperatures once again a possibility.  Death Valley
was the big winner Wednesday with a 126F high temperature.
Meanwhile, the observed 115F high at McCarran airport in Las Vegas
yesterday was the hottest high temperature since July 2013, and very
similar temperatures are expected once again today.  Increasing
moisture and cloud cover will allow temperatures to cool slightly
Friday but those same clouds may result in more elevated overnight
lows, so for this reason I`ve extended the excessive heat warning
into Friday.  Be prepared for dangerous heat by avoiding the
outdoors until cooler parts of the day and staying hydrated.

The biggest fly in the ointment with regards to temperatures will be
cloud cover. Despite relatively meager monsoon moisture in place,
very hot temperatures will result in a marginally unstable airmass
by this afternoon and will allow for isolated terrain driven
convection to develop. Convection may expand further west today than
Wednesday to encompass the Spring mountains and southern Clark
County, as well as parts of Inyo County and the Sierra.  Ive
increased PoPs to be more in line with convective allowing guidance
which suggests isolated high based storms forming (much like
Wednesday) across these regions during the afternoon today. Moisture
content will slowly climb on Friday and I expanded slight chance
PoPs to include some of the desert valleys.

.LONG TERM...Saturday through Wednesday.

Indications from the medium range models still support the inherited
trend of increasing moisture and instability leading to improving
thunderstorm chances this weekend and early next week across the
Mojave Desert region. Only minor changes were made to the POP/WX and
temperature grids.

There are a lot of complexities and uncertainty in the overall
pattern which is common for this time of year. Attention is
primarily focused on the abundant moisture in place and massive
convective complexes occurring over northwest Mexico. The forecast
location of the mid-level high center is not favorable for opening
up the door to a deep southeast flow and ushering this moisture into
the region until possibly Monday. However...both the GFS and ECMWF
depict an easterly wave developing over northern Mexico and moving
across the Gulf of California Saturday and Sunday. It then moves
northwest up the Baja Coast Monday and begins to induce a more
southeast flow into the Mojave Desert region.

The ECMWF depicts 850 dewpoints of 14-16 C surging up the Colorado
River Valley into southern Nevada late Saturday into Sunday. It
should be noted that it has been indicating this trend for at least
the past 4-5 days. The GFS indicates a similar trend...but is not
quite as aggressive with the moisture increase. This will be the
main setup to watch this weekend to see if it comes together.
Meanwhile...a persistent dry westerly flow is forecast across the
southern Sierra into south central Nevada Monday through the middle
of next week in the base of a mean Pacific Northwest trough. This
will keep moisture confined primarily to eastern San Bernardino
county...southern Nevada and northwest Arizona after Monday.

Temperatures will lower through the weekend with the moisture
increase and remain in the 100-105 degree range across most of the
Mojave Desert region through next week.


&&

.AVIATION...For McCarran...Very hot again today with temperatures of
110F or greater expected much of the afternoon and evening.  Winds
should favor diurnal trends with easterly components expected from
mid morning through mid afternoon before switching in the evening.
High-based thunderstorm activity is expected over the mountain
terrain, with a very low (less than 15 percent) chance of impacting
the valley.  Thunderstorms will impact the various approach
corridors at times.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Very hot temperatures expected for all TAF sites today
and Friday which will cause density altitude issues. Otherwise...
fair weather with very isolated high based thunderstorm activity
expected particularly over the mountainous terrain. Thunderstorm
activity appears unlikely at any of the TAF sites themselves, but
should they occur surface wind gusts over 35 knots will be possible.


&&

.FIRE WEATHER...Very hot conditions expected areawide through Friday
before a return to more typical mid-summer heat resumes. Isolated
thunderstorms will be possible over the mountainous terrain today,
and some storms may produce several lightning strikes but limited
rainfall. Increasing monsoon moisture will result in expanding
thunderstorm coverage over the weekend.  Winds will be fairly light
aside from some afternoon breezes or thunderstorm outflows.


&&

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

&&

$$

Short Term/Aviation/Fire Weather...Outler
Long Term...Adair

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