Heat in Nevada, August 4, 2022

Area Forecast Discussion
National Weather Service Las Vegas NV
833 PM PDT Wed Aug 3 2022

.SYNOPSIS...Thunderstorms will focus on the higher terrain today,
with the best chances near and north of Las Vegas. Higher chances
for storms are expected areawide Thursday through Friday, with the
main threats being heavy rain and flash flooding. Temperatures will
trend down beginning Thursday as moisture increases.
&&

.UPDATE...A few strong storms did manage to develop today producing
locally heavy and flash flooding. But right now, radar activity is
trending downward. Some hi-res model show rain showers moving back
into parts of Mohave and San Bernardino Counties after midnight with
a larger swath of showers and embedded thunderstorms developing over
the area tomorrow morning. Flash Flood Watch is already posted for
parts of the area the next two days with expansion possible. Will
let next shift make that call once all model data is available.

&&

.SHORT TERM...Through Friday.

Isolated thunderstorms this afternoon will quickly diminish this
evening. In general, expecting a quiet night however a few
showers may push through Mohave and Clark counties early Thursday
morning on the leading edge of a moisture push. These should be
low impact and isolated.

Pieces are coming together for an impactful few days of weather
across the Southwest US for Thursday through at least Friday. Main
concerns will be heavy rain with flash flooding.

Current mesoanalysis and satellite imagery show a complex of
storms forming over southern Arizona. This feature is expected to
shift north through the area overnight tonight, helping to usher
in moisture as it does so. In addition to the moisture being
pushed in with this MCV, models also show the main area of high
pressure shifting east and settling in over the Four Corners
region by Thursday morning, which would allow for moisture
southerly flow to set up over the region. By Thursday morning, the
HREF has high probabilities for all of eastern California,
southern Nevada, and arizona to have 1in PWATS, and even shows
high probabilities for over 1.5in of PWAT through San Bern,
Clark, and Mohave counties creeping in during the day Thursday. By
Thursday night, 2-3 standard deviations anomalous PWATS will be
in place across the region, with the highest anomalies in
California through Esmeralda and Nye counties. Overall, high
confidence that very moist air will be in place over the region
Thursday through much of Friday. We may lose some of the moisture
Friday late afternoon, however still should see at least 1in PWATs
for much the region.

With all this moisture in place, models continue to show a piece of
energy rotating around the mean flow Thursday through Friday.
This will be a driving factor in our precipitation development,
and in my experience, models tend to underplay precipitation
chances and impacts with these shortwaves in monsoon. Thinking
that thunderstorms will develop Thursday afternoon due to
instability and the previously mentioned decaying MCV.
Thunderstorms will then continue overnight as the wave rotates
into the regions, with the highest confidences for continued
thunderstorm chances over California areas. Continued
thunderstorms chances/redevelopment is expected Friday afternoon,
especially in Inyo County into the Southern Great Basin as the
mesovort shifts northward. Convection should diminish Friday
evening and overnight.

With high moisture and forcing in place, there is increasing
confidence for thunderstorms with heavy rain that will produce flash
flooding over parts of the region. Highest confidence in flash
flooding impacts is associated with the shortwave, so issued a
Flash Flood Watch for Thursday afternoon through Friday for areas
in California and southern Nevada that could see several rounds of
heavy rain due to synoptically driven features. This is where
ECMWF EFIs and GEFS M-Climate are showing a strong signal for
anomalous QPF. This is also where the highest PWAT anomalies will
be. Elsewhere, held off on issuing a watch but that does not mean
one will not be needed in the future. Of note, some of the high
res models show a complex of storms moving out of Arizona into
Clark County Thursday night. Its not well handled on the models
currently with varying solutions of where this complex of storms
will set up and how much rain it will produce, but if this complex
of storms does come together- it could produce higher impacts the
areas it moves through and a watch may be needed. Also, there are
a lot of mesoscale features that may enhance
precipitation/thunderstorm impacts, so will need to continue to
watch the overall environment and hi-res models as we ingest more
data and get closer to the event.

.LONG TERM...Saturday through Tuesday.

Moisture will remain in place through the weekend into early next
week, with 1.25 - 1.50 inches of PWAT over southern Nevada and the
ECMWF/GFS ensemble means continuing to pull over 2 inches up into
Yuma. GFS forecast soundings indicate that the bulk of this moisture
will remain in the mid-levels, with inverted V soundings elevating
forecast DCAPE above 1500 J/kg. That said, what happens this weekend
will be dependent on shower and thunderstorm activity Thursday into
Friday. Monsoon activity on those days could work to moisten the
lower levels or result in an MCV formation with an associated
outflow or vort max, and/or work over the environment enough to
stifle convection over the weekend. At this time, neither the ECMWF
or the GFS ensemble means indicate much in the way of easterly waves
riding along the ridge in the long term, a feature that we often
rely on to spark widespread convection during the monsoon. This is
subject to change with any MCVs that form over northern Mexico and
southern Arizona this week, but helps to give context to what can
change between now and this weekend.

In general, expect a couple more rounds of monsoon activity through
the forecast period, but specific impacts this weekend are unknown
at this time.
&&

.AVIATION...For Harry Reid...VFR will prevail over the next 30
hours. Variable winds will become predominantly southerly with
speeds largely below 8 knots. SHRA is expected across western
portions of the Vegas TRACON today around 21 UTC, but confidence
is not high enough to include explicitly in the TAF this
afternoon. We'll have to monitor any erratic outflow winds if SHRA
develops west of the terminal. Southerly winds will become
variable during the overnight hours with southerly flow expected
to return Thursday. The potential for convection is greater on
Thursday (tomorrow) and I've inserted a mention of VCSH around 21
UTC, though VCTS may be needed if instability forecasts increase.
Gusty/erratic outflow will be the main threat, though MVFR vsby
cannot be ruled out with TS.

For the rest of southern Nevada, northwest Arizona and southeast
California...VFR will also prevail at the remainder of the
aerodromes over the next 24 hours. Occasional cigs between
FL150-250 are forecast with lower cloud decks INVOF SHRA/TSRA. the
greatest potential for convection will be at KBIH where satellite
shows developing CU along the higher terrain. There will be a 2-4
hour potential for TSRA at this airfield and I've included a
TEMPO group to address this. There's a non-zero chance for
convection INVOF other TAFs, but probabilities remain under 15%.
Otherwise, southerly winds will increase along the CO River Valley
with speeds in the 10 to 12 knot range. Gusts to near 20 knots
cannot be ruled out. Stronger westerly winds with gusts to near 25
knots are forecast across southern San Bernarino County.
&&

UPDATE...Pierce

SHORT TERM...Nickerson
LONG TERM...Varian
AVIATION...FGZ Forecaster

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
802 PM PDT WED AUG 3 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0740 PM     FLASH FLOOD      5 SE KEELER             36.43N 117.83W
08/03/2022                   INYO               CA   LAW ENFORCEMENT

            CALIFORNIA HIGHWAY PATROL REPORTED WATER,
            DIRT AND ROCKS IN THE ROADWAY. APPROXIMATELY
            2 TO 3 CARS STUCK DUE TO THE ROADWAY BEING
            IMPASSABLE.

&&

BKP