Severe Thunderstorm Warning 5, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
314 PM PDT Sat Jul 16 2022

.SYNOPSIS...Monsoon moisture persists through the weekend,
continuing the potential for monsoonal thunderstorms to the
region, favoring the higher terrain. Afternoon storm chances will
continue through early next week, as will above-average
temperatures. A brief lull in monsoonal moisture will occur mid
to late week, dropping rain chances and confining them more to
Arizona but a return of moisture looks to occur heading into next
weekend and early next week.

&&

.AFTERNOON UPDATE...
After collaboration with neighbors, opted to issue a Heat Advisory
for tomorrow for some of the northern zones (Lincoln/N. Mohave) as
heat risk was solidly in the "high" category for the lower
elevations of those areas. Further south, where these temperatures
are not as uncommon, heat risks should be lesser tomorrow for the
general population. Of note, overnight lows are well above average
across the region meaning some risk for compounding heat effects
exists across the region regardless, but wanted to highlight these
more uncommon locations in Lincoln and Mohave counties such as
Littlefield, Caliente, Alamo, Hiko, and Colorado City.

.SHORT TERM...Today and Tomorrow.
As of 18Z, satellite and radar trends showed convective initiation
underway over high terrain of southern Nevada, SE California, and
northwest Arizona. While moisture isn't as impressive as
yesterday, there is still plenty of it in place to convect
efficiently with heating alone. WPC has included almost all of the
CWA (except San Bernardino) in a marginal risk for flash flooding
which is only slightly less expansive than SPCs general thunder
risk for today as well. This illustrates well that any convection
will have the possibility for isolated heavy rainfall and thus,
flash flooding. That being said, any other dynamic triggering
mechanism other than orographics is lacking pretty much entirely
today so expect this risk to continue to be mostly confined to
the high terrain areas.

Beyond flash flood risk, with the drier sub-700 mb layer present
today, there will be more of a concern for gusty outflow winds.
DCAPEs of 1500+ J/KG are prevalent across the CWA according to the
RAP mesoanalysis. With little to no shear, we should see several
radial outflows produced from initial convection and then those
outflow creating new updrafts, especially as they interact with
other topography. 12Z HREF shows less than a 10% chance for 50+ kt
outflow winds this afternoon, and max values topping out around
40kts. This seems appropriate given the limited UL support today.

For tomorrow however, some additional variables may come to play
to aid in a bit more upscale threat. The 250mb high spinning over
the Sierra today will shift northeast and serve to pull an
inverted trough axis northwest from northern Mexico. This axis
will be the trigger for convection tonight and overnight in Mexico
that should also be pulled up tomorrow morning into the Great
Basin. Should this complex generate any MCVs or additional outflow
boundaries, we could be seeing either maintained convection
overnight, or an earlier onset of convection tomorrow morning.
Increased PoPs to include some slight chance mentions overnight
and tomorrow morning as well to capture this.

.LONG TERM...Next Week.
While the overall H5 ridge meanders around the desert southwest
next week, PWAT values decrease across much of the area and even
fall to below normal for a brief period late week per ensemble
meteograms. With the high pressure still in place, heating will
stay above average with subtle vort energy wrapping around the
high. This will set the stage for at least a few days of dry
conditions and confine PoPs to Arizona for the most part. Even
Mohave may have a dry afternoon or two Thursday or Friday, and
rely on convection to the east to kick off outflows for any
precip.

However, the 00z/06Z EC/GEFS/GEM all seem to agree with bringing
the monsoonal moisture back by the weekend or early next week with
QPF signals returning to KIGM and pretty much all sites across the
CWA by early next week. CPC 6-10 and 8-14 day outlooks both
indicate a signal for above normal precip in agreement with the
long term ensembles as well.

&&

.AVIATION...For Harry Reid...Expect a southerly component to the
winds into the evening hours around 8 kts. Winds will favor more of
a southeast direction early then southwest by late afternoon.
Isolated thunderstorms are expected around the area with the main
operational impacts likely being the potential for outflow winds to
impact the terminal during from mid afternoon through early evening.
Variable winds up to 25 kts will be possible with any outflow. FEW-
SCT120 expected through the day. Similar conditions are expected on
Sunday.

For the rest of southern Nevada, northwest Arizona and southeast
California...Thunderstorm chances will be mainly confined to
southern Nevada, northwest Arizona, the portions of northern Inyo
County and far eastern San Bernardino County this afternoon and
early evening. Storms will be capable of brief heavy rain and
outflow winds up to 40 kts. FEW-SCT100-120, but could lower to
around 8-10k feet under any storms. The KBIH terminal has the
highest chance of seeing impacts from thunderstorms. Outside of
thunderstorm influences south to southwest winds 5-15 kts expected.
Similar conditions are expected on Sunday.

&&

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

DISCUSSION...TB3
AVIATION...Czyzyk

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

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