Severe Thunderstorm Warning 53, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
835 PM PDT Thu Aug 18 2022

.SYNOPSIS...Thunderstorm chances will continue through Saturday
before high pressure building in from the Pacific brings a temporary
break Sunday through Tuesday. Locally heavy rain will be possible
with thunderstorms, with the greatest risk in and east of Mohave
County. Temperatures will hover slightly below normal, more so in
areas which see the most clouds and rain.
&&

.UPDATE...Another fairly active day in the 2022 Monsoon book with
activity generally focused across our eastern zones today favoring
Lincoln, Clark, Mohave, and far eastern San Bernardino counties.
While several pockets of heavy rainfall were noted and a few strong
storms, the most robust activity held off until the end of the day
when storms fired near Lake Havasu and developed southward into an
increasingly hot and moist airmass in place over the lower river
valley. These storms produced some very heavy rainfall and wind
gusts of 50-60 mph from Lake Havasu City to Parker Dam.

While that activity has drifted south into Riverside county,
additional activity has begun to develop across Clark and southern
Nye counties, seemingly in conjunction with the 500mb trough axis
extending through southern Nevada. This activity is light and fairly
shallow, though a few lightning strikes will be possible through the
evening hours before activity wanes.

Drier air begins to filter in from the west tomorrow, with activity
likely trending more isolated- though a few strong storms and heavy
downpours will remain possible.

-Outler-

&&

.SHORT TERM...through Friday night. Midday satellite loop showed
thunderstorms over northern Mohave County and the Spring Mountains,
spotty deeper cumulus over the Sierra and Lincoln County, and
scattered shallower cumulus elsewhere. Surface obs showed light
winds and mixed temperature and dewpoint trends, mostly influenced
by the presence/absence of convection now versus 24 hours ago.
Mesoanalysis suggests that Clark and Lincoln counties will light up
this afternoon, as lifted indices are -3 to -6 and debris clouds are
minimized. Mohave County may take a bit longer as debris clouds
erode, but storms immediately to the east will track west and/or
eject outflow boundaries westward, helping to ignite new storms.
Outflow boundary interactions could keep Mohave County storms
bubbling all night, while storms elsewhere should quiet down after
sunset. Friday could get interesting as mid level drying spreads
overhead from the west. This will result in steepening lapse rates,
potentially allowing stronger storms to develop, but also reducing
the risk of widespread flash flooding as precipitable water drops.
Although isolated flash flooding is probable in Mohave County both
today and Friday, the threat does not look widespread enough to
warrant a Flood Watch. Temperatures both days will be below normal
in areas which get clouds and rain, and near to above normal in
areas which see sun all day.

.LONG TERM...Saturday through Wednesday.

A tropical disturbance that originated in the Gulf of Mexico
continues to progress westward across northern Mexico as we head into
the weekend. With previous years' tropical systems that have had
similar progressions during the monsoon, there have been observed
moisture surges, as well as increased upper-level dynamics to assist
with the coverage and intensity of monsoonal thunderstorms. For this
reason, we have been paying close attention to how models resolve
this tropical feature as it pertains to Desert Southwest weather.
Unfortunately, there is still substantial uncertainty in the
details, but confidence is increasing regarding synoptic features
that help give us a better idea of what we can expect.

Both ECMWF and GFS ensemble means indicate that a building area of
high pressure in the Pacific off of the coast of southern California
will shift eastward through the weekend. As the ridge pushes
eastward, it will stifle precipitation chances for much of the
Desert Southwest - particularly across the western Mojave Desert and
southern Great Basin. PWATs in these areas will quickly drop by
about a half inch as dry air moves into the region. Additionally,
this ridge will essentially stall the tropical moisture over
southern Arizona, preventing the previously anticipated moisture
surge into our forecast area. That said, as noted in the previous
forecast discussion, the ridge will continue to build through the
weekend into next week, extending across Arizona, which will choke
off the lifting mechanism associated with the stalled tropical
feature. When this happens, the remnant system will have the
capacity to kick off vorticity maximums northwestward through
Arizona. PWAT values across northwestern Arizona, southeastern
California, and southern Nevada fail to drop below an inch through
the weekend. This sufficient moisture coupled with vorticity
advection and daytime heating would result in the potential for
thunderstorm activity in our forecast area.

Details regarding location, timing, and magnitude are all very murky
at this time, but it is worth noting that a building ridge does not
necessarily mean we are out of the woods with regard to this
tropical feature. Our highest confidence regarding impacts - should
they occur - would be in Mohave County, along the Colorado River
Valley, and portions of eastern San Bernardino County where moisture
and proximity to possible vort lobes would warrant higher PoPs.

Otherwise, the long term forecast looks much drier than the past
couple of weeks as the ridge of high pressure continues to expand
eastward. Late week, there is indication that the center of the high
will cut off over the Four Corners region, returning our favorable
monsoon flow - a solution that the NBM seems to favor.
&&

.AVIATION...For Harry Reid...With the exception of the 20Z to 02Z
period, sustained winds are expected to remain light, 10 knots or
less. These light winds will tend to follow typical diurnal trends
with brief periods of more variable winds. Between 20Z today and 02Z
Friday, vicinity thunderstorms will form in the mountains around the
Las Vegas Valley. These storms will have the potential to move off
of the higher terrain and into the valley, with a chance of
thunderstorms and rain impacting the terminal between 21Z and 01Z.
Even if the storms do not move directly over the terminal, it is
likely that they will see impacts from gusty 30 knot outflow winds.
The direction of the outflow winds will depend on the location of
the storms around the valley.

For the rest of southern Nevada, northwest Arizona and southeast
California...KVGT and KHND will be similar to KLAS, with relatively
light and diurnal/variable winds. The exception to this being the
20Z to 02Z period where thunderstorms and outflow winds have the
potential to impact each terminal. KBIH will favor a northerly
direction with 15-20 knot wind gusts possible later this afternoon
and evening. KDAG will follow diurnal trends with 8-12 knot
sustained winds. Vicinity thunderstorms will begin to pop up around
KDAG beginning as early as 21Z. KEED and KIFP will favor a southerly
direction with sustained speeds around 8-12 knots. The Colorado
River Valley TAF sites will have the potential to be impacted by
gusty outflow winds, thunderstorms, and rain between 21Z and 02Z.
The direction of these outflow winds will depend on the location of
the storms around or in the terminal area.
&&

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

SHORT TERM...Morgan
LONG TERM...Varian
AVIATION...Stessman

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
645 PM PDT THU AUG 18 2022

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

0638 PM     TSTM WND GST     2 WSW LAKE HAVASU CITY  34.47N 114.35W
08/18/2022  M58 MPH          MOHAVE             AZ   MESONET

            A WIND SENSOR NEAR THE LONDON BRIDGE IN LAKE
            HAVASU CITY MEASURED A 58 MPH WIND GUST AT
            6:38 PM. DATA COURTESY OF EARTH NETWORKS.

&&

MW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
742 PM PDT THU AUG 18 2022

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

0728 PM     FLASH FLOOD      5 SSW GOLDEN VALLEY     35.16N 114.24W
08/18/2022                   MOHAVE             AZ   COUNTY OFFICIAL

            A COUNTY OFFICIAL REPORTED SIGNIFICANT
            FLOODING AT SHINARUMP DR AT THE SACRAMENTO
            WASH. THE FLOODING WAS ESTIMATED TO BE 100
            YARDS WIDE.

&&

ASG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
916 PM PDT THU AUG 18 2022

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

0530 PM     FLASH FLOOD      26 NNW NEEDLES          35.17N 114.85W
08/18/2022                   SAN BERNARDINO     CA   DEPT OF HIGHWAYS

            HEAVY ROADWAY FLOODING REPORTED BY CALTRANS
            WHICH CAUSED REPORTING PARTY VEHICLE TO
            DRIFT INTO OTHER LANES. TIME ESTIMATED BY
            RADAR.

0730 PM     TSTM WND DMG     EARP                    34.16N 114.30W
08/18/2022                   SAN BERNARDINO     CA   LAW ENFORCEMENT

            CHP REPORTS POWER LINES DOWN FROM HIGH WINDS
            ALONG PARKER DAM ROAD. TIME ESTIMATED BY
            RADAR.

0828 PM     FLASH FLOOD      EARP                    34.17N 114.31W
08/18/2022                   SAN BERNARDINO     CA   LAW ENFORCEMENT

            CHP REPORTED FLOODING BLOCKING ROADWAY ON
            HIGHWAY 62 AND PARKER DAM ROAD AS WELL AS
            ROCKSLIDES ALONG PARKER DAM ROAD.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
919 PM PDT THU AUG 18 2022

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

0454 PM     FLASH FLOOD      10 ENE OATMAN           35.07N 114.22W
08/18/2022                   MOHAVE             AZ   DEPT OF HIGHWAYS

            W OATMAN HIGHWAY CLOSED FROM MILE MARKER 40
            TO E SILVER CREEK ROAD DUE TO FLOODING. TIME
            IS BASED ON RADAR.

&&

ASG

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
934 PM PDT THU AUG 18 2022

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

0700 PM     FLASH FLOOD      1 WSW LAKE HAVASU CITY  34.48N 114.35W
08/18/2022                   MOHAVE             AZ   PUBLIC

            SIGNIFICANT FLOODING WAS REPORTED NEAR THE
            LAKE HAVASU CITY RESORT. VIDEO TAKEN AT THE
            SCENE SHOWS A CAR TRYING TO DRIVE INTO A
            FLOODING SECTION OF ROAD AND THE CAUSED THE
            CAR TO START FLOATING. NO INJURIES WERE
            REPORTED.

&&

ASG