Flash Flood and Damaging Wind in California, September 3, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
109 PM PDT Sun Sep 3 2017

.SYNOPSIS...Isolated to scattered showers and thunderstorms are
expected again this afternoon. Another storm complex with strong
winds may develop near Kingman and move across Lake Mead and Lake
Mohave this afternoon. High pressure will begin to build across the
region Monday. However, low-grade monsoon moisture trapped under the
ridge will result in continued chances for terrain-driven showers
and thunderstorms each afternoon through the week.
&&

.SHORT TERM...Through Tuesday.

Ample moisture remains in place this afternoon for shower or
thunderstorm activity to develop just about anywhere. Stronger
instability is present along the Colorado River Valley as well as
southern Mohave and eastern San Bernardino counties. As CIN
erodes this afternoon, expect one or more storm complexes to form
over these areas. The most likely scenario seems to be fairly
similar to what was seen yesterday with storms congealing in the
Kingman area moving west to northwest towards Lake Mohave and Lake
Mead. DCAPE values progged to be between 1200-1800 J/kg will
result in storms capable of producing strong, possibly severe,
outflow winds across the lakes and perhaps across the Las Vegas
Valley late this afternoon or early this evening. As of 1230 PM,
cumulus was just beginning to develop across the high terrain
across the region. Storms are likely to fire around 1 PM with the
main period of concern between 2 PM and 7 PM today.

Convection is likely to diminish this evening with the loss of
heating. However, a few showers may linger or a precipitation band
associated with the remnants of Lidia could brush southwest San
Bernardino County.

For Monday and Tuesday, high pressure will being to build across the
region. Low-grade monsoon moisture is likely to become trapped
underneath resulting in terrain-driven shower/storms. Temperatures
will also warm a few degrees each day, back to well above normal for
early September.

.LONG TERM...Wednesday through Sunday.

The latest medium range models have backed off on bringing a deep
trough into the our region next weekend. They now indicate a
persistent southerly flow that will keep moisture and instability
over much of the forecast area from the middle to end of the week
with only a slight downward temperature trend. An amplified ridge of
high pressure over the western states Wednesday will be flattened a
bit Thursday and Friday as troughing along the West Coast moves
inland over the Pacific Northwest. A mean area of high pressure is
expected to hold over the Four Corners region while a trough remains
off the west coast. The resulting southerly flow will keep
sufficient moisture over the region for slightly varying chances of
afternoon and evening thunderstorms primarily over the mountains.
&&

.AVIATION...For McCarran...Winds will favor a typical east to
southeast direction through the early part of the afternoon.
Confidence in the forecast then decreases as thunderstorms begin to
develop across the area. At the moment, looks like the best chance
for thunderstorms will be over Mohave county after 19Z, with storms
that do develop over this area moving northwest. While widespread
thunderstorm activity isn't expected around Las Vegas at this
time, cant rule out some scattered storms later this afternoon. In
addition, strong outflow winds out of the south or southeast are
possible from the decaying storms that do move out of Mohave
County after 02Z tonight. Once winds diminish late this evening,
typical overnight winds are expected.

For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated to scattered thunderstorms are expected across
the region today, especially this afternoon and evening in the
Kingman to Bullhead City area. Colorado River Valley sites are the
most likely to be impacted by thunderstorm activity. Storm motion
will be toward the northwest and will likely produce gusty and
erratic winds this afternoon and evening.
&&

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

Short Term...Wolcott
Long Term....Adair
Aviation.....Allen

For more forecast information...see us on our webpage:

http://weather.gov/lasvegas or follow us on Facebook and Twitter

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
1225 PM PDT SUN SEP 3 2017

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

0731 PM     TSTM WND DMG     COTTONWOOD COVE         35.49N 114.68W
09/02/2017                   CLARK              NV   PARK/FOREST SRVC

            *** 1 FATAL ***
            LAKE MEAD DISPATCH CENTER REPORTED A DEATH
            CAUSED BY CONDITIONS BROUGHT ABOUT FROM THE
            HIGH WINDS ASSOCIATED WITH SEVERE
            THUNDERSTORM ACTIVITY. AN ADULT MALE BECAME
            ENTANGLED IN THE MOORING LINE OF A HOUSE
            BOAT THAT BROKE LOOSE DURING HIGH WINDS AND
            WAS DRAGGED UNDER THE WATER AND DROWNED.

&&

TL