Area Forecast Discussion
Issued by NWS Las Vegas, NV

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS65 KVEF 231126

Area Forecast Discussion
National Weather Service Las Vegas NV
426 AM PDT Tue Jul 23 2019

.SYNOPSIS...Monsoon moisture will continue to spread into the
region today through Thursday. Each afternoon, showers and
thunderstorms continue to look likely across much of the area
which will be capable of strong outflow winds, localized heavy
rainfall, cloud to ground lightning, and small hail. This pattern
should begin to shift by late Friday resulting in drier and hotter
conditions by the weekend.


.SHORT TERM...Through Friday morning.
So far this morning, light rain and occasional thunder have been
observed as an outflow and wave from earlier convection in Arizona
pushes west. While this would likely be a feature of additional
development, and to a point it has been, the atmosphere is quite
stable this morning and this activity has difficulty overcoming
this and the very dry lowest 300 mb. That being said, the coverage
of light returns on radar is substantially more than depictions
the NBM produced and thus, more reliance on CAMs have been taken
with the forecast moving forward.

Keeping this in mind, there seems to be quite a bit of agreement
in afternoon convection across the CAMs, synoptic models, and
local models in one form or another. This is to be expected now
with PWATs this afternoon eclipsing 1.5" as far north as KLAS per
the RAP and increased instability as a result of surface dewpoints
reaching the 50-60+ range. By and large the overall PoP forecast
is largely the same, but one feature that has stood out is the
development of convection across northern Mohave County late this
afternoon per many different models. It appears a local vorticity
maximum will be enough to initiate convection west of the
Hualapais and tap into an area of CAPEs over 1000 j/kg, 0-6 km
shear around 25 kts, and strong lapse rates. While these details
vary between one model to another, the all agree on maintaining
very strong DCAPE environments. So whether or not a multi cell
cluster develops (HRRR) or a mature MCS develops (NAMnest), the
possibility for strong outflow winds appears quite possible in
these areas. If this indeed comes to fruition, which confidence is
fairly high given the model agreement, then potentially 50+ mph
winds will be pushing quickly northwest and possibly impacting
Lake Mead, Cottonwood Cove, and possibly the Las Vegas Valley.
Timing of this is not quite as confident but sometime in the
21Z-03Z time frame appears to capture the majority of the timing
in which this occurs in various model depictions. So it will be
this feature we keep the closest eye on this afternoon and
evening, but isolated convection elsewhere is still possible,
especially in the higher terrain of Clark, Mohave, and Inyo

As this aforementioned vort max round the bend of the parent upper
high, it will push into southwest Utah and should take the
majority of this complex with it marking a downtrend in convection
overnight. However, depending on how much outflow generation takes
place in the afternoon and evening, convection may be continuing
through at least the late night hours if not the early morning.
This activity should be an order of magnitude less intense with
the loss of heating and instability, but likely more coverage than
this morning.

Another round of convection is expected Wednesday afternoon and
evening with again the favored areas being northwest Arizona, and
the higher terrain areas of Inyo and Clark counties. According to
GEFS plumes, the highest PWAT of the week should be Wednesday
afternoon and if the 06Z NAM12 is to be believed, well over 2"
values in the southern Colorado River Valley. Thus, the concern
rises on Wednesday evening for more prevalent heavy downpours.

One more opportunity for convection again Thursday afternoon but
PWAT values should be declining as the main upper high begins to
cut off the moisture tap from Mexico. The better moisture profiles
shift northward Thursday, this time favoring south-central Nevada
and southern Utah. Thus the best chances for afternoon convection
look more like the higher terrain of Clark and northward instead
of southward like Tuesday and Wednesday.


.LONG TERM...Friday through the Weekend.
The ridge of high pressure will begin to move southwest with the
center of circulation over southeast CA by Saturday morning. As the
ridge makes this southwestern shift, drier air will move northeast
across our local region through the weekend which will help scour
out some of the lingering moisture. This regime should keep mostly
slight chances limited to the northern edges of our CWA Friday
afternoon. Just something to note, in the past models have been too
quick with scouring out moisture, so there is low confidence that
other portions of our CWA won`t see convection Friday afternoon,
especially across the higher terrain. Drier and warmer conditions
are expected through the weekend and into early next week as the
ridge meanders overhead. Ensembles are hinting that a shortwave
digging off the western Pacific early next week would help nudge
the ridge eastward with the center around the Four Corners by TUE-
WED. This would result in the monsoon set-up again possibly
returning low level moisture to the region by the end of the week.


.AVIATION...For McCarran...A push of southerly winds with
occasional gusts to 18-20 knots is expect through 11-12Z this
morning. Winds will continue to favor a southerly direction through
the morning but may flop between southeast and southwest as winds
decay through the morning. Through the afternoon, isolated to
scattered thunderstorms will be possible in and around the Las Vegas
Valley. With any thunderstorms that develop, erratic and gusty
outflow winds will be possible. There is a slightly better signal
for a shift to the east-southeast Tuesday evening originating from
distant thunderstorm outflow winds, but confidence remains low on
these winds reaching the terminal and their potential magnitude at
this time. Otherwise, expect diurnal southwest winds Tuesday night,
generally remaining below 10 knots. BKN to OVC skies aoa 10 kft
through the period. With any thunderstorms that move over the
terminal, lower ceilings to 7000-9000 kft may be possible.

For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered light showers will continue to move northward
across the region through the morning. VCSH is expected near KIFP
and KEED later this morning, with all other TAF sites expected to
remain dry. More widespread thunderstorm chances are expected this
afternoon where VCTS is expected to impact every terminal at some
point today. With any thunderstorms that develop, erratic and gusty
outflow winds will be possible. Besides outflow wind potential,
winds should remain  Similar to yesterday, there is a slight
possibility of thunderstorms in western AZ sending outflow winds
toward the Colorado River this evening which could impact KEED and
KIFP, but little confidence of these winds reaching the terminals at
this time. BKN to OVC skies aoa 9 kft through the period.  &&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures. Reports of wind damage, reduced visibility due to dust
storms, hail, or flooding impacts are all greatly appreciated.




For more forecast information...see us on our webpage: or follow us on Facebook and Twitter is the U.S. government's official web portal to all federal, state and local government web resources and services.