232
FXUS65 KVEF 151945
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
1245 PM PDT Wed May 15 2024

.SYNOPSIS...Scattered showers and a few isolated thunderstorms will
pose a gusty wind threat for areas along and south of I-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.

&&

.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
vort 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 PacNW and the EPac 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 EPac low with the PacNW
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.

&&

$$

DISCUSSION/AVIATION...Woods

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