Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 260350

Area Forecast Discussion
National Weather Service Las Vegas NV
850 PM PDT SAT JUN 25 2016

.SYNOPSIS...Hot weather will continue through the weekend under
high pressure. A trough of low pressure passing by to the south will
bring the first influx of monsoon moisture next week, with slight
chances for thunderstorms beginning in Mohave County Monday and
spreading over much of the region by Wednesday and Thursday. This
will also bring slightly cooler and more humid conditions.

.UPDATE...Quiet evening across the area. No updates needed to the
forecast.  &&

313 PM PDT SAT JUN 25 2016

.SHORT TERM...Through Tuesday night. Very little change to previous
thinking. High pressure remains in firm control through tomorrow,
with changes beginning Monday and continuing through Tuesday. First
concern is the heat. Temperatures remain well above normal, but this
is the time of year when heat warning criteria are also rising since
we are well into the typical hot season. Thus, despite temperatures
expected to be at or over 110 degrees in the Las Vegas Valley and
the normally hotter areas such as the Colorado River Valley on
Monday and Tuesday, the Heat Impact Level grids are still showing
mainly 2s with sprinklings of 3s and 4s. This suggests that we will
be just a hair short of formal warning criteria, but temperatures
this hot still pose a threat, especially since it has been so hot
for so long (today may be the only day in a ten day stretch that
KLAS does not reach at least 109 degrees). With this in mind, chose
to issue an email briefing about the heat. Second concern is
thunderstorms. Inverted trough sliding west along the international
border passes by Monday, allowing the moisture to begin seeping in
from the southeast for slight chances of thunderstorms mainly in
Mohave County Monday afternoon and evening. Chances should spread to
areas roughly along and east of a line from Yucca Valley to Mount
Charleston to Caliente on Tuesday. The moisture influx will bring
higher dewpoints, but temperatures will probably only come down
significantly in areas which receive rain.

.LONG TERM...Wednesday morning through Saturday.

Confidence continues to increase for thunderstorm chances later this
coming week.

Return flow on the western side of a building high pressure
ridge over the southern Rockie mountains will cause an increase in mid-
level and low-level moisture across the area beginning on Tuesday.
The mid-level moisture will work into the area from the east as an
inverted trough works across the south side of the mid-level high
pressure Monday though Tuesday. On Wednesday...models indicate a
fairly stout heat low strengthening over the desert southwest US that
will increase the southerly wind coming off the Gulf of California.
This is likely to cause a gulf surge and increase low level moisture
enough to amplify thunderstorm chances particularly on Wednesday and
Thursday and likely lasting through Saturday.

Chances for thunderstorms were increased in the forecast for this
forecast issuance. All other elements were tweaked...but remain
similar to previous forecast.

.AVIATION...For McCarran...Light and variable winds through the
afternoon. If any direction is predominant, easterly will be most
likely. Winds should come around to south southwest this evening and
overnight. Smoke from fires in nearby states will reduce slant range
visibility, but probably not surface visibility.  This pattern
should continue through Monday, with thunderstorm chances arriving
to the local mountains Tuesday.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Smoke from fires will remain aloft in most areas,
reducing slant range visibility but probably not surface visibility
except in high terrain. Expect typical diurnal winds in most areas
with no significant clouds or weather through Sunday. Thunderstorm
chances will begin in Mohave County Monday and spread to much of
the region by Wednesday.

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



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