303
FXUS65 KVEF 160250
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
750 PM PDT Wed May 15 2024

.SYNOPSIS...Scattered showers and isolated thunderstorms will
pose a gusty wind threat for areas along and south of Interstate 15
today. The work week ends warm and dry, with Las Vegas making a run
at 100 degrees on Friday. Gradual cooling and increasing winds ensue
this weekend and into next week as low pressure develops over the
region.
&&


.UPDATE...Scattered showers and isolated thunderstorms across the
Mojave Desert this afternoon are beginning to wane with the sunset.
The low levels remained very dry, with DCAPE measured around 1700
J/kg in the 00Z sounding, so most showers failed to produce enough
rain to reach the ground. The exception to this was the higher
terrain of Mohave County. Gauges on the Hualapai Mountains measured
between 0.08 and 0.16 inches of rain today. Some cells produced
frequent lightning as well as gusty winds between 20 and 30 mph, but
no cells approached severe criteria this afternoon. Remnant showers
in eastern San Bernardino and central Mohave counties will continue
to dwindle over the next few hours. No changes made to the forecast
this evening, as it looks to be in good shape.
&&


.PREVIOUS DISCUSSION...1245 PM PDT Wed May 15 2024/

.SHORT TERM...Today through Friday.

Main story today will be the isolated-to-scattered showers (and
possibly a storm or two) along and south of the I-15 corridor. A
vorticity max diving south through Utah will interact with remnant
moisture associated with the closed low over the San Diego / Baja
California area. Convective initiation will favor the local high
terrain, with outflow winds more likely to move into surrounding
valleys than actual precipitation. As moisture (particularly in the
low-levels) is so limited, not concerned with heavy rain or flash
flooding from this activity. Instead, any threat posed by convection
will likely be from lightning or outflow winds. RAP forecast
soundings show deep, inverted-V profiles with DCAPE of 1500+ J/kg,
supporting efficient evaporation in the sub-cloud layer and
enhancing downdraft potential. This is reflected in the 12z HREF
probabilities of 30+ knot winds, which paint a wide swath of 10-30%
chances along and south of I-15, along with a small area of 50%
chances in southern Mohave County this evening as activity
consolidates there. Rain chances completely exit our CWA around
midnight, ushering in a dry period that lasts at least a couple days.

This dry period ensues because high pressure begins to build over
the region. 500mb height anomaly charts show modest positive
anomalies over the W/SW US on Thursday and Friday, sandwiches
between a cutoff low in the Eastern Pacific and a shortwave over the
Northern Rockies. These height rises and the general "breeziness" of
the zonal/NW flow pattern will allow Las Vegas to make a run at its
first 100 of the year on Friday. Latest NBM probabilities of
reaching 100 degrees stand at 50% and Death Valley has a 25% chance
of reaching 110. Needless to say, it`s going to be pretty warm out
there, with Minor-to-Moderate HeatRisk across the area.

.LONG TERM...This weekend into next week.

As an additional shortwave enters the Pacific Northwest and the
eastern Pacific low begins to move towards shore, our ridge will
slowly break down over the weekend. This allows temperatures to
gradually cool while breezy conditions persist. By the start of the
work week, ensemble guidance is in pretty good agreement, phasing
the eastern Pacific low with the Pacific Northwest shortwave. As
this occurs, temperatures return to seasonal values (possibly a few
degrees below normal) and winds increase. The best chance of wind
impacts looks to be across our western deserts, with 50-80%
probabilities of 40+ mph winds Saturday - Monday. Elsewhere,
impactful wind chances peak on Monday with generally 25-50%
probabilities. At least some degree of troughing is forecast to
linger across the Western US through most of next week. The depth
and southward extent is less clear, which will impact temperatures
and winds during this time. This uncertainty is evident in NBM box-
and-whisker plots of high temperatures, with a ~10 degree spread
between the 25th and 75th percentiles. The same plots for peak wind
gusts show 15-20 knot spreads. However, we can generally expect
temperatures to be within a few degrees of normal and at least
breezy conditions to persist through most of the week.
&&


.AVIATION...For Harry Reid...In the absence of any convective
influence, expecting light winds to persist from a NNW - NNE
direction. However, there is potential outflow winds from vicinity
precipitation to reach the airport. The first chance comes this
afternoon between 21z and 00z, and is dependent on if anything can
develop off the Sheep range to the north. The second chance comes
later this evening (~06z) from distant convection in SW Utah. This
second wave seems to have more model agreement (roughly 60% chance)
and would likely be stronger. Latest NBM guidance suggests gusts up
to 20 knots are possible. With both outflow scenarios, wind
direction should be from the N or NE. By 09z, any outflow influences
should cease, leaving light N breezes less than 10 knots to persist
through the night, becoming NE tomorrow morning. FEW-SCT clouds aoa
10kft this afternoon and evening, becoming clear overnight.

For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated to scattered showers and storms may influence
conditions (mainly winds) at sites in the Las Vegas and Colorado
River Valleys this afternoon and evening. In the Vegas Valley,
outflow potential exists this afternoon with any vicinity
convection, with a better chance (~60%) late in the evening as
outflow from distant activity tries to move into the valley. Any
outflow winds should be from the N or E. Similar story for KEED and
KIFP, though the outflow direction is more likely to be from the
west this afternoon and east this evening. Outside of convective
influences, these sites should see typical light and diurnal wind
patterns. At KDAG, light NE winds this afternoon with the typical
westerly push arriving around 02z with gusts of 20-25 knots. At
KBIH, north winds increase to 15-25 knots this afternoon, weakening
overnight. VFR conditions prevail with FEW-SCT clouds aoa 10kft.
&&


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

&&

$$

UPDATE...Varian
DISCUSSION/AVIATION...Woods

For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter