Areal Flood Advisory 7, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
100 PM PDT Tue Jun 29 2021

.SYNOPSIS...Increasing monsoonal moisture will lead to chances for
showers and thunderstorms each day through Thursday. The main threat
in the Sierra and southern Great Basin today will be dry lightning
before the deeper moisture arrives tonight, while the main threats
in much of the Mojave Desert will be high winds and flash flooding.
The highest chances for widespread precipitation will be Tuesday and
Wednesday before the moisture slowly retreats the second half of the
week. Cooler temperatures are expected through Thursday before a
drying and warming trend returns this weekend into next week.
&&

.SHORT TERM...
Current hi-res models have a complex of precipitation continuing
overnight, likely similar to or a bit more robust than what we saw
last night. However, confidence is low in this forecast as short-
term models are split on how long convection will persist overnight.
This will play a big role into Wednesda's forecast. If we keep the
clouds and showers through the night, then Wednesday's thunderstorms
chances will be limited and better chances will displaced north of
our area.  If the precipitation ends around midnight like some of
the models show, then Wednesday afternoon will likely have another
round of showers and thunderstorms. Flash flooding threat looks to
be slightly higher tomorrow compared to today as PWATs increase
again overnight with another moisture push and storm motion is
forecasted to be slower than the past few rounds of convection. If
anything develops in southern Clark, Mohave, and southeast San
Bernardino counties Wednesday, they could produce flash flooding.
The wind threat for that same area should be lower tomorrow
though as we better saturate the low levels. Further north where
dry air near the surface will likely still exist, sudden gusty
winds will be the main concern.

The Red Flag Warning for fry thunderstorms will likely be allowed to
expire at 8pm as a better push of moisture is likely this evening
and overnight. HREF shows PWATs up to an inch push into the
region by tonight. Otherwise, temperatures on Wednesday should be
cooler than today, and maybe even below normal in some locations
where clouds persist through much of the day.

The low confidence in the forecast continues for Thursday, as
again Wednesday's storm activity will influence Thursday's
overall expectations. In general, heights should rise through the
day as high pressure builds in slowly from the southeast. This
will likely dry out things a little, though some moisture should
remain in place over the region. Ensembles differ on how much
moisture will remain over southern Clark into Mohave counties
Thursday, with ECMWF ensembles show a high chance for PWATs over
1inch still in place over that region...but the GEFS showing it
drying out quicker and the 1inch PWAT probabilities are far less.
Thursday has some potential for another round of thunderstorms,
but definitely not a slam dunk either.

.LONG TERM...Friday through Monday.

Tropical moisture from the remnant tropical system Enrique lingers
south of the area through the long term with the GEFS mean
forecasting anomalously high precipitable water pooled across much
of our area. 1.5-2.0 inch mean PWATs are forecast in the region just
south of our southern CWA border on Friday with the 1-1.5 inch mean
line extending across central and eastern San Bernardino County,
over much of Clark County and southern and central Mohave County
Friday afternoon. The moisture profile based off the GEFS mean is
largely unchanged through the weekend before an eastern Pacific
trough moves in from the west bringing drier air to much of the area
on Monday except in the far southeast CWA where the probability of 1
inch PWATs are in the 50-70 percent range. Temperatures are forecast
to hold steady right around normal Friday through Sunday then
warming a few degrees to above normal on Monday. However, it is
worth noting the uncertainty given the fairly large temperature
spread.
&&

.FIRE WEATHER...Dry low levels/inverted-V soundings will remain
in place through early this evening before the better moisture
works its way in, so thunderstorms this afternoon and evening will
likely start as dry then transition to wet by tonight. Even
though there is a short window for dry thunder, the extremely dry
fuels justify erring on the side of caution. Sudden gusty winds
are also possible with any of these storms, so new fire starts
could easily be spread. Better moisture will spread across the
entire region by tonight, with improving RHs likely Wednesday.
&&

.AVIATION...For McCarran...Scattered thunderstorms are
expected to develop later this afternoon and evening over southern
Nevada. There is still a good potential to see a thunderstorm
complex producing wind gusts over 35kts and CIGS of 6 to 8k feet
move near or over the terminal this evening. Winds should go
variable once again overnight before southeasterly winds return
tomorrow, along with the chance of more thunderstorms.

For the rest of southern Nevada, northwest Arizona and southeast
California...Prevailing south to southeast winds are expected over
much of the area this afternoon with speeds 10-15 kts. Scattered
thunderstorms are expected to develop this afternoon and evening
over the Sierras and southern Nevada leading to gusty and erratic
winds at times through the evening. Some isolated gusts up to 40kts
will be possible with stronger storms along with CIGS to around 6k
feet. Typical diurnal winds are expected later tonight and tomorrow
morning before the threat of more storms returns.
&&

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

SHORT TERM...Nickerson
LONG TERM...Salmen
AVIATION...Planz

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

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