Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 270053
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
553 PM PDT SUN JUN 26 2016

.SYNOPSIS...High pressure is expected to shift north over the next
couple of days as a weak disturbance moves east across northern
Mexico. This will allow for some moisture to work into the region
bringing an increasing chance of thunderstorms through at least
midweek. Temperatures are expected to cool a few degrees with the
additional cloud cover expected.
&&

.UPDATE...Afternoon convection over Arizona associated with an
inverted trough just south of the AZ border has produced some cloud
cover that is working its way into Mohave County and southern San
Bernardino County. I updated sky conditions to reflect this.
Otherwise forecast is on track. One other item of note, several hi-
res models are indicating the potential outflow from convection in
Arizona to push westward and into Mohave County and eastern Clark
County late tomorrow afternoon and early evening. We`ll be
monitoring how this evolves and the potential for blowing dust to
be an in issue, particularly in and around dry lake beds.
&&

.PREV DISCUSSION...
230 PM PDT SUN JUN 26 2016

.SHORT TERM...through Wednesday night.

An upper disturbance over northern Mexico will continue to slowly
shift west and northwest over the next couple of days. This will
shift the center of the high further north and east and allow for
the winds to become more southeast. This will help bring in our
first taste of monsoonal moisture. There was a slight increase in
dewpoints down the Colorado River Valley earlier today, but that
moisture was rather shallow and dewpoints have lowered significantly
this afternoon. The real moisture push will begin tomorrow as PW
values start to increase from the south. By Monday afternoon the 1
inch PW line stretches from Kingman to Searchlight to Barstow and by
Monday night and Tuesday most of Mohave, Clark, southern Nye and San
Bernardino Counties will range from 0.75 to 1 inch with a few
pockets over an inch. Instability remains rather marginal with
Mohave County seeing the best instability. However, the disturbance
currently over northern Mexico should help to enhance thunderstorm
development. Coverage is expected to be rather limited Monday
afternoon with southern Mohave and far southern portions of San
Bernardino seeing the higher chances. As the disturbance lifts north
Monday night we could see some nocturnal thunderstorms develop
across portions of San Bernardino, Clark, and Mohave Counties. At
this time, we are only expecting isolated thunderstorms as coverage
should be limited.

As this disturbance lifts north the better chances of storms will
also lift north. Isolated storms are possible across Inyo, Nye and
Lincoln Counties with storms also possible over the higher terrain
of Clark and Mohave Counties. The deeper moisture is expected to
shift east on Tuesday, so its possible a few of these storms will
only produce little or no rainfall.

The models become a bit less clear on Wednesday. The GFS wants to
bring in some drier and more stable air with any thunderstorm
chances limited to the far eastern portions of the cwa. The NAM and
ECMWF want to keep the moisture in place and continue to chances of
afternoon thunderstorms over the area. There is a trough digging off
the west coast and it we have enough of its influence in place then
moisture may get shifted east. However, am currently inclined to
keep at least a slight chance of storms. Temperatures will remain
several degrees above normal, but any clouds that develop could help
knock temperatures down a few degrees. At this time afternoon
temperature records are not in jeopardy, but overnight lows
certainly could.

.LONG TERM...Thursday through Sunday.

Main concern through the period will be monsoon moisture and
associated thunderstorm chances. Moisture will already be in the
eastern half or so of the area at the beginning of the period.
Models generally agree on a very weak trough trying to move into the
area from the west on Thursday, bringing westerly flow which may be
enough to prevent moisture from making it any farther west, but not
strong enough to scour the moisture out of the eastern zones. Models
remain in general agreement through Saturday in keeping the moisture
gradient in place across our CWA, with dry conditions in the western
zones and moisture and thunderstorm chances lingering in the eastern
zones. Model differences become more pronounced on Sunday as low
pressure moves into British Columbia. This low may, or may not,
increase the southwesterly flow enough to scour moisture out of our
area Sunday and/or Monday. How this plays out may end up depending
on whether MCSs over Mexico or Arizona end up pushing the moisture
farther north and west than expected in the meantime.
&&

.AVIATION...For McCarran...Light winds will transition to a
southwest flow with speeds around 7 kts overnight. Light northeast
winds around 6-7 kts after 19z on Monday. A few clouds around 10-12k
feet over the Spring Mountains with a slight chance of thunderstorms
affecting the Peach Spring Corridor.

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 into Monday morning.
Thunderstorms will be possible across Mohave and far southern San
Bernardino Counties Monday afternoon. Wind speeds will remain below
10 kts.
&&

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

$$

Update...Czyzyk
Short term/Aviation...Gorelow
Long term...Morgan

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