Flash Flood and Damaging Winds in Nevada, July 17 to 18, 2023

Area Forecast Discussion
National Weather Service Las Vegas NV
1132 AM PDT Mon Jul 17 2023

.SYNOPSIS...Showers and storms possible this afternoon for areas
along and north of the I-15 corridor, as well as the Arizona Strip.
Strong outflow winds and lightning are the main concerns. Convective
activity shifts poleward tomorrow, primarily focused in our northern
areas and the AZ Strip. Outside of any precipitation, excessive heat
will continue through the week across the Mojave Desert and
northwestern Arizona.
&&

.SHORT TERM...Today and Tuesday.

The 500mb high has retreated into east-central AZ, allowing south-
southeasterly flow to advect in more moisture. This is not only
evident in the increased mid-level clouds, but surface observations
as well. 24-hour dewpoint changes at 16z are as high as +25 degrees
in the Las Vegas Valley. This morning's 12z sounding recorded 0.85"
of PWAT, a jump of over 0.5" from yesterday at 12z. Increased
moisture and cooler temperatures aloft due to the retreating high
will fuel isolated to scattered afternoon thunderstorms. Model
guidance continues to show convection focused along/north of the I-
15 corridor, as well as the Arizona Strip, though I would not
completely rule out an isolated storm or two farther south. Modeled
instability wanes with northward extend, so convection in Inyo, Nye,
Esmeralda, and the northern half of Lincoln Counties should be less
robust than storms along the I-15 corridor. 12z HREF mean depicts
CAPE values of 250-750 J/kg over most of San Bernardino, Clark,
Mohave, and southern Lincoln Counties. As excessive heat continues
in the presence of modest moisture, deep inverted-V profiles with
DCAPE values around 2000 J/kg will exist across the area. This means
any shower/storm will likely produce gusty outflow winds. Given the
parameter space and expected storm coverage, the best chance of
severe thunderstorm winds is the I-15 corridor from Barstow to
Mesquite. HREF confirms this analysis by placing 10% probability of
50kt wind contours in this area. Fortunately, dry low-levels will
mitigate flash flood potential. As far as timing goes, convection is
expected to develop around 1pm, and wane around sunset. Storms are
possible once again Tuesday afternoon, but activity is expected to
be focused in the northern 1/3 of the area, as well as the AZ Strip.
Similar to today, gusty winds and lightning will be the main
concerns.

Outside of any convective activity, excessive heat will persist,
particularly for the Mojave Desert and northwestern AZ. Tomorrow's
temperatures should cool sufficiently for the Excessive Heat Warning
to be expired in Lincoln, central Nye, and Esmeralda Counties.
Elsewhere however, dangerous heat is expected to continue into next
weekend, with Major to Extreme HeatRisk lingering. As such, the
Excessive Heat Warning for these areas was extended until Saturday.

.LONG TERM...Wednesday through Sunday.

Drier southwest flow continues to look more probable over most of
our region Wednesday through Friday compared to Monday and Tuesday
as ensemble means indicate our strong ridge to shift more over
eastern Arizona/New Mexico and Texas. EC/GEFS PWAT anomalies shift
to below normal through the end of the week and begin to recover
heading into next weekend. During this time, high temperatures will
vary only a few degrees up or down, but remaining at major to
extreme heat risk levels, especially with the duration of these
above normal temperatures persisting several days. Thus, the
Excessive Heat Warning has been extended through Saturday.

Heading into late next weekend and early next week, there continues
to be little sign of significant temperature relief other than
increased moisture moving into the region. Day 8-9 cluster analysis
indicates that the western ridge will reposition itself and deepen
yet again, perhaps over the El Paso area. At the same time, PWAT
anomalies now swing to above average setting the stage for potential
monsoon activity. NBM does paint 20-40% PoPs across Mohave by early
next week as well in line with the ensemble suggestions.
&&

.CLIMATE...

Daily Temperature Records:

			*Record High (Most Recent Year of Occurrence)*

CITY        |Mon (7/17)
------------|----------|
Las Vegas   |116 (2005)
------------|----------|
Kingman     |113 (2005)
------------|----------|
Needles     |125 (2005)
------------|----------|
Daggett     |117 (1998)
------------|----------|
Bishop      |107 (2006)
------------|----------|
Death Valley|127 (2006)

For Las Vegas:

All-time record high: 117 (2021, 2017, 2013, 2005, 1942)
All-time record warm low: 95 (2013, 2005)
Consecutive days at or above 110: 10 days (1961)
Consecutive days at or above 115: 4 days (2005)
&&

.AVIATION...For Harry Reid...Gusty, south to southwest winds can be
expected through this afternoon, with isolated areas of convection
possible mid-afternoon through early evening.  Most of this activity
is likely to remain over the higher terrain surrounding the Vegas
Valley, but erratic outflow winds from the storms may impact
operations at the field, most likely between 3 PM and 7 PM when
gusts to 40kts are possible.  Any thunderstorm activity that does
develop should end by sunset.  Winds will remain southerly overnight
into Tuesday morning before becoming gusty out of the south again
Tuesday afternoon.  Outside of thunderstorm activity, no significant
cloud cover is expected.

For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated areas of convection are possible this
afternoon, mainly across the higher terrain north of I-15 in Nevada
and California.  Gusty and erratic outflow winds to 40kts are the
primary concern with any storms that do develop.  Away from
thunderstorms, winds generally less than 15kts following typical
diurnal patterns are expected, along with a few clouds AOA 15kft.
&&

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

SHORT TERM...Woods
LONG TERM...TB3
CLIMATE...Woods
AVIATION...Planz

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