Weather Service Report


821 
FXUS65 KVEF 010337
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
838 PM PDT WED AUG 31 2016

.SYNOPSIS...Breezy conditions across the region with slight chances
of thunderstorms in northwest Arizona and portions of southern
Nevada expected Thursday through Friday. Dry conditions with
temperatures cooling a little below normal can be expected over the
weekend and early next week.
&&

.UPDATE...MOISTURE WAS CONTINUING TO INCREASE FROM THE SOUTH TONIGHT
AS SEEN IN THE PRECIPITABLE WATER SENSORS AROUND THE REGION. CLOUDS
WHICH HAD DECREASED LATE AFTERNOON AND EARLY EVENING WERE STARTING
TO INCREASE AGAIN, LOOKING AT THE IR SATELLITE LOOP. WHILE HI-RES
MODELS ARE NOT REALLY GENERATING ANY QPF TONIGHT, BASED ON OBSERVED
MOISTURE INCREASE AND CONTINUING MOISTURE INCREASE SHOWN ON THE 00Z
NAM12 AND GFS, I WILL LEAVE SLIGHT CHANCE POPS IN FOR PORTIONS OF
LINCOLN, CLARK AND MOHAVE COUNTIES. CONFIDENCE IN ANY PRECIPITATION
TONIGHT IS PRETTY LOW AND IF IT DOES OCCUR, IT WILL BE LIGHT. SO,
NO UPDATES TO THE FORECAST PLANNED THIS EVENING. -HARRISON-
&&

.PREV DISCUSSION...
244 PM PDT WED AUG 31 2016

.SHORT TERM...Through Friday Night.

The weather maker for the term is a large trough digging down the
west coast. While the bulk of the energy will remain north of the
area, breezy afternoons and chances for thunderstorms are possible
in portions of the area into the weekend.

Moisture is still increasing across southern Mohave county, but a
rather stout subsidence inversion still exists across the area,
keeping too much from happening. By tomorrow this inversion should
begin to erode allowing for greater chances of thunderstorms
especially as a jet streak begins rounding the base of the trough.
There are some concerns regarding thunderstorms tomorrow night.
Although the longwave trough will remain neutral to positively
tilted, the jet streak rounding the base could potentially tilt
shortwaves more toward negative tilt. The right entrance region of
the aforementioned jet will create plenty of lift and favorable
shear profiles of 30 kts + above a modestly moist airmass across
mainly Mohave county overnight. This could lead to thunderstorms
capable of producing wind and small hail in addition to heavy rain.

Overall, expect cooling temperatures and breezy afternoons through
the period, with thunderstorm chances decreasing on Friday.

.LONG TERM...Saturday through Wednesday.

An initial shortwave trough will begin to work its way across the
Great Basin on Saturday and Saturday night and will provide some
gusty southwest winds ahead of the trough, primarily across the
Mojave Desert and northwest plateau of Arizona. Most, if not all of
the low level moisture should be scrubbed out and pushed to the east
on Saturday and I have kept precip out of the forecast. A second
shortwave will move across the area on Sunday, providing another
round of gusty southwest winds to much of the area. Winds are
expected to be slightly stronger on Sunday in comparison to Saturday
and with low RH values some areas may be near critical fire
thresholds. We will need to monitor this closely.  The main trough
of low pressure will remain over the region through Tuesday keeping
a dry westerly flow in place and temperatures several degrees below
normal. The GFS, ECMWF and several GEFS members indicate the
development of a tropical system off of the west coast of Mexico by
mid week next week. The development and evolution of this system
will need to be monitored for the potential of inducing a gulf surge
into the Desert Southwest late next week. 
&&

.FIRE WEATHER...A trough will continue to bring breezy afternoons to
the region into the weekend. Western areas will remain dry, but monsoon
moisture will continue to slowly increase across northwestern
Arizona and extreme southeastern Nevada, leading to thunderstorm
chances through Friday. Winds look to generally stay below any
criteria but will bear watching for later in the week and weekend.
&&

.AVIATION...For McCarran...Southeast winds will likely swing around
to southerly then southwesterly this evening and tonight. Winds may
lighten and up and favor an easterly direction tomorrow morning
before southwest winds develop tomorrow afternoon. Thunderstorms are
possible along the eastern corridors tomorrow and tomorrow night as
well, but likely remaining dry in the Las Vegas Valley.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Breezy to gusty southwest winds will expand in coverage
for tomorrow with chances of thunderstorms across northwestern
Arizona.
&&

.SPOTTER INFORMATION STATEMENT...Thunderstorms are expected to
return to the forecast for at least Mohave County Thursday.
Spotters are encouraged to report significant weather according to
standard operating procedures. 
&&

$$

Long Term..........................Czyzyk
Short Term/Fire Weather/Aviation...Steele

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Western Regional Climate Center, wrcc@dri.edu