Severe Thunderstorm Warning 90, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
205 AM PDT Sat Sep 10 2022

.SYNOPSIS...Remnants of Kay will continue to push moisture into
the region throughout the day and develop scattered showers and
thunderstorms across southeastern California, southern Nevada, and
northwest Arizona. Heavy rain will continue to be the main concern
today, with Flash Flood Watches remaining in effect through late
this evening. Kay's circulation will push eastward on-shore and
bring several days of shower and thunderstorm chances to the area,
favoring south-central Nevada and the Sierra Nevada.

&&

.SHORT TERM...Today through Sunday.
As of 08Z this morning, shower activity has been rather meager
across the region with Kay continuing to weaken off the coast of
California. Despite some impressive UL divergence associated with
Kay's interaction with a longwave trough to the north, this has
not been enough lift to tap into the rich low level moisture
advecting northward into the CWA. It seems as though the strong
convective inhibition in place over the region is squelching the
prospect of much development overnight. Even orographic
enhancement has not helped much. Some of the highest amounts thus
far have been in the high terrain of Morongo Valley, but below 1"
of storm total precip so far and over the course of several hours.

So while the overnight period is disappointing from a rainfall
generation standpoint, there is still plenty of opportunity for
heavy rain development through the next 24 hours. A 20-30kt 850 mb
southerly jet is strongly advecting low level moisture up and into
the southern Nevada this morning. KLAS dewpoints at 0830Z were in
the low 60s and RAP analysis shows this continuing through the
morning. Additionally, GOES17 WV satellite shows dry slotting
taking shape over southern Arizona this morning and HREF mean
cloud cover shows several areas of clearing possible by the mid to
late morning period. Further, a band of vorticity associated with
Kay is developing and slowly moving northward this morning into
the lower Colorado River Valley.

After sunrise, the addition of some differential heating (if
clouds indeed erode) could be enough to get things going along the
aforementioned vorticity band and bring the heavy rain and flash
flooding we have been waiting to unfold. Latest WPC QPF continues
to highlight this area from the Sierra Nevada through Mohave
county as belt of highest QPF through the day today and still
think this makes sense given these features observed. So in
hindsight, the earlier onset of the FFA turned out to be a little
premature, but the continued potential for heavy rain later today
and this afternoon will keep the FFAs in place as originally
issued.

Sunday's forecast remains mostly unchanged, with slightly lower
PWATs across the area with Kay's circulation jaunting southward a
bit. Highest PoPs continue to be over the Sierra and Springs, but
afternoon thunderstorms will be possible across much of the
region. However, HREF and global ensemble QPF is much more
isolated and much less plentiful compared to today. 00Z HREF 6hr
PMM for QPF only show a few high terrain spots including the
Sierra and Panamints with over 0.5" keeping the flash flood
threat much more isolated and marginal in nature.

.LONG TERM...Monday through Friday.

On Monday, ridging over Utah will weaken and push eastward as the
trough associated with the remnants of former Hurricane Kay push
inland. NBM PoPs encompass our entire forecast area on Monday, as
the center of the low passes directly overhead. PoPs continue
through midweek, slowly shifting northeastward as upper-level flow
ushers the moisture away. Thereafter, a much welcomed, dry
southwesterly flow will set up over the region. Shortwave
propagations will likely increase afternoon breeziness in the
latter half of the week, but otherwise, dry conditions are
expected with PWAT values dropping below an inch areawide.
Temperatures will cool as well, with below-average temperatures
expected through the forecast period. There is a good deal of
uncertainty in the extended period, but the NBM seems to be
latching onto the 'Return of the High' solution, with temperatures
increasing back to above-average next weekend.

&&

.AVIATION...For Harry Reid...Southeast wind 8-12 kts, occasional
gusts to 17 kts may be seen the rest of this morning followed by an
easterly wind this afternoon and evening. Precipitation chances
remain tough to nail down as moisture indeed has increased but
dynamics/lift have been slow to develop well away from the cyclonic
rotation of post-tropical cyclone Kay. Latest guidance suggests an
area of light showers develops in and around the valley later this
morning. Thunderstorms are possible later this afternoon and early
evening as the air mass becomes more unstable. Movement of the
showers and thunderstorms will be from east to west. Precipitation
threat looks to end by late evening leaving behind partly cloudy
skies overnight.

For the rest of southern Nevada, northwest Arizona and southeast
California...Expecting a band of showers with embedded thunderstorms
to develop across northwest Arizona, southern Nevada and Inyo County
today. Storm motion will be from east to west. Precipitation chances
look to be lower across San Bernardino and the Colorado River.
Precipitation looks to dissipate by late evening leaving behind
partly cloudy skies. Lowering ceilings with precipitation 5000-8000
ft at times, as well as visibility down to 5SM with any heavier
rain. Southeast-east winds generally 10-15 kts through the
period.
&&

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

SHORT TERM...TB3
LONG TERM...Varian
AVIATION...Pierce

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