Flash Flood Warning 138, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
1218 PM PDT Tue Sep 12 2023

.SYNOPSIS...Another round of thunderstorms is likely this
afternoon and evening, mainly in northwest Arizona and southern
Nevada. The main concern is heavy rainfall, along with strong winds
and frequent lightning. Additional storm activity will taper off the
next two days, becoming dry by the weekend.
&&

.DISCUSSION...Through Next Wednesday.

Skies have started to clear out over southern Nevada and northwest
Arizona, meaning a transition from stratiform rainfall to potential
convective development. Activity should peak between 20Z and 02Z,
though isolated storms have already started to form over mountains
in southern Nevada. Slow clearing of cloud cover over Mohave
County and as a result cooler temperatures over the area may
somewhat delay convective initiation. Once storms do start to
develop, the presence of 35 knots of surface to 6 km shear and
around 1000 J/kg MLCAPE may allow for the development of small
hail and frequent lightning. Afternoon DCAPE values between 1100
and 1400 J/kg mean that gusty outflow winds are a threat as well.
PWATs between 1.0 and 1.4 inches could lead to locally heavy
rainfall, as seen in some storms so far this morning. Convection
seen so far this morning has also mostly been terrain driven, a
pattern expected to continue into the afternoon.

Tomorrow, a ridge of high pressure over the eastern Pacific Ocean
and zonal flow over the Four Corners states will create
northwesterly flow aloft over the forecast area. Shortwaves moving
along this pattern and lingering moisture may lead to additional
isolated thunderstorms on Wednesday and Thursday afternoon. The
ridge of high pressure moves in from the Pacific into the western
United States towards the end of the week, creating dry and stable
conditions over the forecast area Friday and through the weekend.
Long range models are starting to show agreement that low
pressure will move into the Intermountain West sometime in the
middle of next week, but details are unclear at this time. Will
continue to monitor the development of this feature. Temperatures
rise slightly as high pressure builds in, with highs staying
within a few degrees of average. Temperatures begin to fall back
to below average values as the trough starts to influence the
upper level pattern above the forecast area.
&&

.AVIATION...For Harry Reid...A complex aviation forecast period is
expected with scattered showers and storms from 20z today through
02z Wednesday. While confidence is low in the terminal being
directly impacted, at least vicinity thunder is warranted. Gusty
winds and heavy rains to accompany any storm, which would naturally
result in sub VFR conditions. Otherwise winds to shift from
south/southeast through the afternoon, to west in the evening. Wind
speeds to remain 10 knots or less outside of thunderstorms.

For the rest of southern Nevada, northwest Arizona and southeast
California...Showers and thunderstorms to affect eastern terminals,
including KVGT/KHND and KIFP. Activity looks to peak between 20z and
02z. Gusty winds and heavy rainfall to accompany any storm. While
confidence is not sufficiently high for prevailing thunder, several
terminals carry vicinity thunder for several hours. Winds to largely
remain diurnally driven from the south/southwest. KBIH will be the
exception with east/southeast winds through the day, shifting to the
northwest late tonight. Aside from any local thunderstorm impacts,
VFR visibilities and ceilings can be expected.
&&

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

DISCUSSION...Meltzer
AVIATION...Austin

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