Damaging Wind in Nevada, August 8, 2024

Area Forecast Discussion
National Weather Service Las Vegas NV
731 PM PDT Thu Aug 8 2024

.SYNOPSIS...Monsoonal moisture will remain in place through the
weekend helping to fuel afternoon and evening thunderstorms over
portions of southern Nevada, northwest Arizona, and eastern San
Bernardino Counties. Above normal temperatures will continue through
the end of the week high pressure persists over the Southwestern US.
Drier air is forecast to push into the region next week reducing the
thunderstorm chances and bringing slightly cooler temperatures to
the region.
&&

.UPDATE...Scattered thunderstorms developed this afternoon across
the terrain of Clark, Lincoln, and Mohave counties. While extensive
cloud cover kept convection from getting organized, enough weak
instability still exists even at this hour for thunderstorms to
persist in Lincoln County through southwest Utah and northern Mohave
County. This area will need to be watched through the evening as
some models have these storms producing a decent cold pool and
outflow. Area observations do show gusty 25 to 35 MPH northeast
winds in the St George, UT area pushing into eastern Lincoln and
northeast Clark County...So the cold pool exists but will it be able
to push southwest through Clark and Mohave counties tonight is the
question. The 00Z HRRR is concerning, bringing this outflow through
the area with showers and thunderstorms developing in it wake which
then becoming an MCV that persists over Mohave County overnight.
However this is just one of the HRRR and the other runs have been
far less robust. The less robust scenario match up better with other
hi-res CAM models and would make more sense with the given
environment where instability is waning and cloud cover kept things
at bay through the day. Most likely, the northeast winds will
translate through Lincoln, Clark, and Mohave counties through
midnight with low to isolated moderate impacts- including gusts up
to 30 MPH and isolated but brief and unorganized showers and
thunderstorms with heavy rain. Will need to watch how things develop
in the next few hours though as an MCV in Mohave County is not out
of the question and could result in moderate to isolated high
impacts due to heavy, persistent rain leading to flash flooding.
Updated precipitation chances through the night to represent the
most likely trend in showers and thunderstorms.

Otherwise, it will be a quiet night with low temperatures running a
degree or two cooler than last night.
-Nickerson-
&&

.PREVIOUS DISCUSSION...100 PM PDT Thu Aug 8 2024
.SHORT TERM...through Friday night.

Expansive cloud cover that originated last evening over northern
Arizona continues to push west through northern Mohave and Clark
Counties. This has helped to suppress convection under this cloud
shield, but areas that have seen sunshine are starting to fire this
afternoon. Strongest convection so far has occurred over the Spring
Mountains and Sheep Range where radar has estimated over an inch of
rain has fallen so far. We are also starting to see convection fire
over southern Mohave County where a lot of the CIN has eroded and
CAPE values have increased to around 1000-1500 J/KG. With PW values
still around 150% of normal combined with increasing instability, we
will see more widespread afternoon and evening thunderstorms over
northwest Arizona. Convection will likely be delayed until mid to
late afternoon over the higher terrain of eastern San Bernardino and
eastern and central Clark County due to the current cloud cover.
These storms will be capable of producing heavy rain and with DCAPES
around 1000-1500 J/KG gusty outflow winds are also a possibility.

Some convection will be possible through the overnight hours as
little areas of higher vorticity remain over the region. At this
time, nothing looks overly organized, but enough to keep some
thunderstorms going well into the overnight period.

Friday look to have a similar setup as today with good instability,
high PW values and potentially more sunshine to start the day. The
most active areas look to be southern Nevada, northwest Arizona, and
eastern San Bernardino Counties. Winds aloft will remain fairly
light which could lead to more flooding concerns and gusty outflow
winds will also remain a concern through the afternoon.

.LONG TERM...This Weekend through Wednesday.

Thunderstorms chances are expected again Saturday as ample moisture
sits over the region. The highest PWATs will be along and southeast
of the I-15 which is where the highest rick for afternoon
thunderstorms will exist, with a lower but non-zero risk further
west. Will need to watch if the upper level wave that will be
sitting over southwest California will be able to add any forcing
and thus increase convection coverage and impacts. Ensembles still
do not signal for a significant or widespread flash flooding event
with probabilities for 0.50 and 1.0 inch of rain in a 4 hour period
remains low to none (less than 20%). The difference in 24hr rainfall
amounts for Saturday on NBM percentiles is large, but nothing
atypical for monsoon season. The the percentile 24hr rainfall
accumulation for Saturday does paint much of Mohave County with
about 1 inch amounts, so if there was higher impacts it could
potentially be through there however probabilities for over even
0.50 in a 24 hour period tops out at 30% in the terrain. On Sunday,
the moisture will begin to retreat as an upper level trough pushes
into the West Coast, but most areas southeast of the I-15 will hang
to PWATs over 1.00 inch so there is a continued heavy rain though
thunderstorm chances will drop slightly compared to Saturday in
southern Nevada. With modest instability shown on long range models
both days, any storms would also bring the risk for lightning, gusty
outflow winds, and small hail. People with outdoor plans this
weekend in eastern portions of San Bernardino and Nye counties as
well as all of Clark, Lincoln, and Mohave counties should stay up to
date with the forecast and be prepared for thunderstorm impacts.

The upper level trough will continue to move into the West Coast the
beginning of next week with long range models in decent agreement
that the trough will move into California with only slight
discrepancies in its strength. Either way, the flow will turn
southwest which will scour out the moist air across much of the
region. Thunderstorm chances Monday through Wednesday will be
confined to Mohave County and areas east. The trough will also help
cool temperatures with slightly above normal temperatures dropping
to about normal by Tuesday.

&&

.AVIATION...For Harry Reid...Thunderstorms develop along high
terrain around the Las Vegas Valley this afternoon and early
evening. Any storms that form may produce frequent lightning and
gusty outflow winds which would cause temporary changes in wind
speed and direction at the terminal. Outside of storms, winds should
generally be out of the southeast. Gusty southerly winds pick up in
the evening and should shift to the east overnight. If the winds do
not shift east, they most likely maintain a southerly to
southeasterly direction. Variable winds return in the early morning
hours. Outflow winds from storms around the region may influence
wind speed and direction at any time overnight.

For the rest of southern Nevada, northwest Arizona and southeast
California...Thunderstorm development around the Las Vegas Valley
may lead to gusty and erratic outflow winds at KHND and KVGT this
afternoon and early evening. Additional outflow boundaries from
storms around the region may cause change in winds overnight at KHND
and KVGT as well. Outside of thunderstorms, winds should be out of
the east to southeast this afternoon and evening. Storms in
northwest Arizona may not reach the vicinity of the terminal but
should create gusty easterly outflow winds at KEED and KIFP in the
evening. Lastly, thunderstorms over the Sierra should reach the
vicinity of KBIH this afternoon. At KDAG, variable winds this
afternoon turn to the southwest overnight and become gusty,
decreasing early tomorrow morning.

&&

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

&&

SHORT TERM...Gorelow
LONG TERM...Nickerson
AVIATION...Meltzer

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