Severe Thunderstorm Warning 11, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
240 PM PDT Sun Sep 1 2019

.SYNOPSIS...Thunderstorm chances will increase this week as
monsoonal moisture makes a return to the southern Great Basin and
Mojave Desert. Thunderstorm chances will mainly impact areas south
of I-40 this evening, but will gradually push north through the
remainder of the week. Gusty winds and flash flooding will be the
primary threats from these storms. Given increased clouds and shower
activity, temperatures will cool to near normal values for early
September.
&&

.DISCUSSION...through Sunday.

Once again, hot temperatures are impacting the region this afternoon
with readings running several degrees above normal. Today will be
the last day of excessive temperatures as the strong high pressure
that has been sitting over the area shifts east and we also get an
increase in monsoonal moisture. Mid level clouds have generally been
increasing through the afternoon as the moisture starts making its
push northward. Thunderstorms have increased in coverage this
afternoon across central and southern Arizona and have developed
just east of Mohave County. Local hires models have been rather
consistent today in developing a thunderstorm complex that will
track west across southern Mohave County and impact the Colorado
River Valley this evening, likely between 8pm and midnight. Not only
will there be potential of brief heavy rain, but strong gusty winds
will be possible. Some of the models are showing outflow winds
between 40+ mph affecting southern areas of Mohave County through
the Colorado River Valley including Lake Havasu, so boaters should
especially be cautious this evening and prepare for the potential
for strong winds. This complex may continue into southern Nevada,
but indications are that it will weaken significantly, but a few
sprinkles will be possible overnight.

Monsoon moisture will continue to push north over the next few days
resulting in isolated to scattered showers and thunderstorms each
afternoon through the end of the week, especially in the favored
higher terrain. Gusty winds and the potential for flash flooding
will be the biggest concerns as the upper steering flow remains
fairly light through Wednesday. Beyond Wednesday, the models differ
on how quick the moisture gets pushed out of the area. It's possible
that we could see at least a chance of afternoon thunderstorms each
day into next weekend as the trough off the west coast may not move
in as quick. Temperatures will remain near to slightly above normal
through the week.
&&

.AVIATION...For McCarran...Winds will gradually shift to the
south southeast by mid afternoon with gusts of 15-20 knots possible.
Early this evening gusts will taper off as winds shift to the
southwest at around 10 knots or less through early tomorrow morning.
There continues to be a low-end chance of some brief, gusty outflow
winds moving through the valley out of the southeast between 06z-09z
associated with storms over northwest Arizona. If this scenario does
occur, speeds do not look to to be very impactful leaving the wind
shift as the main concern. Light, easterly winds are expected Monday
morning which will then favor the southerly direction during the
afternoon. However, this could change quickly as scattered showers
and storms develop around Clark County between 20z-05z.

For the rest of southern Nevada, northwest Arizona and southeast
California...Outside of shower and storm development, winds will
remain south to southwesterly today and tomorrow with gusts up to
around 20 knots possible both afternoons. Hi-res models continue to
indicated an area of showers and storms moving into Mohave County
later this evening into tonight; pushing towards the Colorado River
Valley terminals. Estimated wind shifts and VCSH have been included
at these locations but confidence is low in these outflow winds
making it all the way up into the Las Vegas Valley. A few showers
could linger into Monday morning with afternoon showers and storms
initiating between 19z-21z. Locally heavy rain, lightning, and gusty
winds will be possible with storm activity Monday afternoon and
evening.
&&

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

DISCUSSION...Gorelow
AVIATION...Guillet

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