279
FXUS65 KVEF 201638 AAA
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
939 AM PDT Fri Sep 20 2024

.SYNOPSIS...A low pressure system moving through the Mojave
Desert will bring scattered to numerous showers and thunderstorms
to much of the region today and tonight. Brief heavy rainfall is
possible with the stronger storms along with gusty winds. Drier
conditions will resume Saturday onward with a warming trend
commencing.

&&

.UPDATE...Isolated showers and thunderstorms that developed over the
western Las Vegas Valley around sunrise have since moved west-
northwestward and are weakening in western Clark County. Latest
development is concentrated in southeast Inyo, northern San
Bernardino County and near Yucca Valley.

Diffluent flow/cold air aloft associated with the upper low
presently over Los Angles will continue to drive storm development
over southeast California the rest of this morning through the
afternoon. New showers and thunderstorms will eventually start to
develop and expand in coverage over southern Nevada and northwest
Arizona this afternoon through tonight as the upper low moves east
through western Arizona tonight. There may be a few showers lingering
in eastern Clark and southeast Lincoln County tomorrow morning
through 8 am PDT, otherwise any shower coverage will be confined to
northwest Arizona tomorrow.

Sent out an updated forecast package using guidance from the 12Z
convective allowing models.


&&

.PREV DISCUSSION...122 AM PDT Fri Sep 20 2024
.SHORT TERM...through Sunday night.

Closed low currently located near the Los Angeles Metro area will
swing eastward today across the Mojave Desert and into northern
Arizona by Saturday morning. As the low passes through, cold air
aloft, modest but elevated moisture content, and strong
dynamically driven lift will encourage widespread showers and
thunderstorms across the region. Precipitation coverage through
mid-afternoon will largely favor the San Bernardino County Deserts
including Barstow- Daggett, Baker, and the Morongo Basin. CAPE
values across these areas will climb into the 500-750 j/kg range
resulting in isolated stronger storm cores, and with 500mb temps
of -15 to -16C, a few instances of small hail are possible as
well.

By this evening, as the low shifts into the lower Colorado River
Valley, strongest divergence aloft and overall most favorable
upper level forcing will move into southern Nevada and northwest
Arizona. Sunset through midnight represents the approximate best
window for precipitation in the Las Vegas metro, with showers and
thunderstorms tending to taper from west to east late Friday night
into Saturday morning. Instability won`t be quite as significant
after dark which suggests a tendency for more dominant shower
activity as opposed to thunderstorms after sunset, though a few
lightning strikes will remain possible well into the night. In
addition, with lingering dry air in the low levels, locally gusty
winds will be possible especially in advance of the developing
shower activity. Overall precipitation expectations remain fairly
minimal, with a trace to a tenth of an inch most common, though
some areas observing stronger storms especially across San
Bernardino and Mohave counties could see locally heavier rainfall
totals.

Aside from some lingering morning showers in Mohave County, drier
conditions will resume over the weekend as the low departs to our
east. Temperatures remain slightly below normal on Saturday before
returning closer to normal Sunday as heights climb slightly.


.LONG TERM...Monday through Thursday.

Models are in much poorer agreement than 24 hours ago, and the
overall forecast pattern has changed somewhat, so confidence is
lower than average. Although there is general consensus on high
pressure moving into the West from the Pacific, there are
important differences on the east side of the ridge. Several of
the ensemble members have now latched onto one or more of the
following ideas: weak low pressure developing on the southern
flank of the high in the area of Southern California, tempering
our warming trend and introducing some clouds, and/or another
shortwave trough diving down the front side of the ridge,
amplifying over the Four Corners area and possibly retrograding
westward, which would bring a chance of light rain showers to at
least our eastern CWA. That being said, a majority of the ensemble
members still keep our area dry, so there`s only a slight chance
at the moment. Run to run trends will be important. Temperatures
should still rise above normal in areas which don`t see showers,
although not quite to the degree which was expected earlier. The
most likely scenario should be highs in the mid 90s for Las Vegas,
but a few degrees cooler if substantial cloud cover materializes.

&&

.AVIATION...For Harry Reid...Light winds this morning will turn
southeast by mid-day and continue from that direction into the early
evening.  Once the winds turn to the southeast, sustained wind
speeds of 7 to 11 knots are anticipated, and there is a 30%
probability of occasional gusts to 15 knots after 21Z.  Scattered
showers and a few isolated thunderstorms are also expected this
evening and early tonight, with the best chance of thunderstorms
occurring after sunset.  Storm chances should end by 08Z, but a few
showers may linger through the night.  Prevailing winds are expected
to turn southwest after sunset, but gusty outflow winds from any
storms that do develop could impact the terminal area through the
evening night.  Sky conditions will range from scattered to broken
today with bases AOA 8kft AGL, followed by improving skies overnight
with bases lifting to around 12kft AGL by daybreak Saturday.

For the rest of southern Nevada, northwest Arizona and southeast
California...Low pressure moving across southern California today
and northwest Arizona overnight will bring the threat of showers and
thunderstorms to the region.  KDAG will see showers and storms
develop early this afternoon, followed by the Colorado River TAF
sites by late afternoon and early evening.  A few storms are also
possible in the Las Vegas Valley after sunset.  Conditions will
improve by Saturday morning, with all but the far eastern sections
of the region seeing precipitation chances end.  Aside from gusty
winds near thunderstorms, winds will be from the southeast to
southwest in most areas, with sustained speeds of 12 knots or less.
Winds at KBIH will be primarily from the north through the TAF
period.   Sky conditions will range from scattered to broken today
with bases AOA 8kft to 10kft AGL, followed by improving skies west
to east overnight with bases lifting to around 12kft AGL by daybreak
Saturday.

&&

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

&&

$$

UPDATE...Pierce

SHORT TERM...Outler
LONG TERM...Morgan
AVIATION...Planz

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