Damaging Wind in Nevada, August 11, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
250 PM PDT Fri Aug 11 2017

.SYNOPSIS...
Showers and storms will be possible today and tomorrow across the
I-15 corridor southward with isolated strong to severe storms
possible. Stronger storms will be capable of producing torrential
downpours and strong wind gusts. Moisture shifts eastward Sunday
with storms primarily over northwest Arizona before dry pattern
settles over the entire region for much of the upcoming work week.
Near normal temperatures expected.

&&

.SHORT TERM...Today through Saturday.

Storms have begun developing along a moisture gradient sitting
just north if the I-15 corridor early this afternoon. PWAT values
across the airmass to the south of I-15 remain in the 1.00-1.60
inch range with uninhibited CAPE values of 1000-1500 J/kg which
are expected to continue to rise over the next few of hours with
full sun for much of the day so far. As activity increases there
is a continued chance for isolated strong to severe storms with
flash flood potential and strong wind gusts. High DCAPE values are
present, supported by dry mid-level air, and potential for
training and slow moving storms will support rain rates of
1.00-2.00 inches per hour. Flash flood threat will be slightly
higher across southern Mohave, southern Clark, and San Bernardino
County as storm motion will likely be slower than storms that
develop to their north. Weakening trend is expected in storm
activity around sunset with little activity expected overnight.

Saturday shows little change in the airmass across the area
except for a possible shift to a more vertical orientation of the
moisture boundary as mid-level trough begins its dry push as it
approaches the west coast. Moisture boundary should set up near
the western boundaries of Lincoln and Clark counties and down into
eastern San Bernardino County. Showers and storms will develop
east of this boundary with highest chances across Mohave County
and the higher elevations of Clark County with more isolated
activity possible in the lower elevations elsewhere. There will
be continued potential for isolated strong to severe storms
tomorrow with similar threats in flash flood potential in heavy
downpours and strong winds with little change in storm
environment. Only difference will be strengthening southwest flow
as jet strengthens and drifts southward on Saturday afternoon
providing some additional shear to work with. Storms could
continue into Saturday night across Lincoln and northern Mohave
County.

.LONG TERM...Sunday through Thursday.

Still a bit concerned about possible tropical influence on Sunday,
but maybe a bit less so than in previous days. Some of the models
have latched onto the moisture push produced by the remnants of
Franklin, but there are also signs that the deep moisture will be
stopped somewhere near the international border by drier southwest
flow thanks to low pressure swinging through British Columbia. Low
level moisture is still expected to be in place roughly along and
southeast of I-15, and the drier air aloft plus some vertical wind
shear could make conditions more favorable for severe thunderstorms
than for very heavy rain. As the low progresses across western
Canada and another wind max dives down from the Gulf of Alaska, the
drier air will make eastward progress Sunday night into Monday,
confining thunderstorm chances to Mohave County. From Monday night
through Thursday, a break in the summer monsoon is expected, with
dry weather and lower humidity. Temperatures Sunday and Monday will
be dependent on thunderstorms, and should be near mid-August normals
for the rest of the period.

&&

.FIRE WEATHER...
Scattered showers and storms will be possible along the I-15
corridor southward today and tomorrow with isolated strong to
severe storms possible each day. Stronger storms will have the
potential for strong wind gusts and flooding rainfall. Mid-level
trough will begin to push moisture and rain chances eastward on
Sunday with afternoon activity confined primarily to Mohave
County. Dry weather is expected area-wide Monday through much of
the upcoming week with near critical RH values along the Colorado
River Valley westward each afternoon. Prevailing flow will remain
out of the south to southwest between 10-15 mph gusting around 20
mph each day.

&&

.AVIATION...For McCarran...Thunderstorms have begun to develop
in the mountains and are expected to continue until 00z-02z. With
thunderstorms surrounding the valley, gusty outflows will likely
impact the terminal from various directions through the
afternoon/early evening. There is a decent chance that thunderstorms
will develop near/over the terminal through the afternoon. Once
storm activity decreases winds should begin to favor a south to
southwesterly direction with speeds ranging between 7 to 12 knots.
This evenings southwesterly should trend to a westerly flow
overnight tonight. Tomorrow will start similar to today, with a
southeasterly wind developing around 15z-17z trending to a southerly
wind by the early afternoon. Thunderstorms will likely develop again
in the mountains, bringing another potential day of thunder in the
vicinity of the terminal. Confidence is low on any storms impacting
the terminal directly tomorrow. Outside of thunderstorm influences,
CIGs should remain around 12kft.

For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered thunderstorms likely through the rest of the
afternoon east of a KDAG-KELY line with convective turbulence and
gusty surface winds likely. Further west dry conditions and breezy
southwest winds expected during the afternoon. Overnight, light
southerly winds expected for most sites, though wind speed and
direction will be influenced by thunderstorm outflow in the area.
Tomorrow morning and afternoon a south wind will develop across most
areas trending to more southwesterly in the early evening hours.
Thunderstorms will be likely again tomorrow and will be focused
mainly east of Interstate 15.

&&

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

SHORT TERM/FIRE WEATHER...Guillet
LONG TERM....Morgan
AVIATION...Boothe

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
229 PM PDT FRI AUG 11 2017

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

0115 PM     TSTM WND GST     2 WSW TWENTYNINE PALMS  34.13N 116.09W
08/11/2017  M68 MPH          SAN BERNARDINO     CA   TRAINED SPOTTER

            TRAINED SPOTTER IN TWENTYNINE PALMS MEASURED
            A WIND GUST OF 68 MPH.

&&

ASG