Lightning Strike in Arizona, July 22, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
145 PM PDT Sat Jul 22 2017

.SYNOPSIS...Warm and generally dry conditions will give way to a
more unsettled pattern starting Sunday night as a push of monsoon
moisture moves in. Widespread showers and thunderstorms are a
possibility Sunday night into Monday before gradually trending drier
through the week. Best thunderstorm chances will be generally across
Northwest Arizona and southern Nevada with more isolated activity
further west. By the end of the week...thunderstorm chances will be
primarily limited to the higher terrain.
&&

.SHORT TERM...Today through Tuesday.

Challenging forecast so low confidence in the details but things are
shaping up for a period of unsettled weather across the region,
particulary Sunday night through Tuesday.  In the very near term,
watching convection develop this afternoon across Lincoln and Mohave
counties and the thinking from this morning remains the same.
Anticipate scattered storm activity to develop and potentially push
a westward moving outflow across Clark county later this evening,
perhaps pushing as far west and south to impact the Colorado River
Valley as well. Not expecting this outflow to trigger a lot, but a
few pop up showers and storms may form along and behind the outflow,
so I'll maintain some low chances for showers this evening across
most of Southern Nevada and the lower Colorado River valley.

Tomorrow, conditions overall look very similar to today, maybe a
notch more moist. But the general evolution should be similar with
convection again favored in Lincoln and Mohave counties, and little
more activity across the Clark county mountains. A few isolated
storms are also expected across the Sierra and northern Inyo county
mountains.  Things get more interesting Sunday evening and
overnight, as forecast models suggest the atmosphere becoming
increasingly unstable overnight as moisture steadily rises through
the early morning hours. Models often struggle to resolve convective
details in this pattern, but suspect some MCS activity or at least
scattered overnight convection to develop across Northern Arizona
and push into southern Nevada/eastern California overnight.  With
this in mind, I kept low/moderate PoPs going overnight Sunday into
Monday morning.

Monday has the greatest potential for widespread storms, but the
threat is highly conditional as we will likely wake up to
considerable cloud cover across the region which will inhibit
destabilization. Without some extra forcing from a MCV or vorticity
max, it may be hard to generate strong storms. If we do get storms
however, flash flooding will be a big concern given the abundance of
moisture.

Tuesday...drying will begin to work in from the west but the drying
will mainly be in the mid and upper levels. This may actually make
Tuesday more favorable for storm activity given the better chance we
will see enough sunshine to generate storms.  Flash flooding will
remain a concern.

Overall....be prepared for the possibility of strong thunderstorms
over the next few days, and any of these storms will carry an
attendant threat for strong downburst winds and flash flooding.
Daily thunderstorm chances will be heavily dependent on cloud cover,
and it's likely at least one of the next few days ahead will see
suppressed storm activity due to widespread clouds.

.LONG TERM...Tuesday through Friday.

For Wednesday and beyond expect gradual drying and warming
conditions as weak southwest flow sets up. Chances for
showers/storms will exist each day, but are likely to become
increasingly limited to the high terrain as the week progresses. By
next weekend, there are some indications monsoon moisture will begin
to creep back into the region as return flow sets up around the
western US ridge, but the exact positioning will be critical in
influencing our regions chances. So stay tuned.

&&

.FIRE WEATHER...Increasing thunderstorm chances will be the primary
focus of the next few days. Scattered thunderstorms mainly limited
to Lincoln and Mohave counties will spread westward Sunday night
through Tuesday with elevated thunderstorm chances everywhere. In
addition, widespread clouds and improved RH recoveries are expected.
Conditions will gradually dry out midweek onward with thunderstorm
chances becoming increasingly limited to the higher elevations.

&&

.HYDROLOGY...
Creeks, streams and rivers in northern Inyo County have shown
decreasing flows over the last couple of days. However, some road
closures continue in the area. Bishop Creek Bypass and Big Pine
Creek Bypass continue to be utilized to minimize flows through
Bishop and Big Pine. Remember, never drive through flooded
roadways or around barricades. Also, pastureland or farmland
adjacent to creeks, streams or rivers could experience areas of
standing water.

&&

.AVIATION...For McCarran...Winds should mainly favor a typical
diurnal pattern through Sunday with east to southeast winds during
the day and south to southwest winds at night. Speeds should be less
than 10 knots. The only exception could be potential outflow winds
from thunderstorms mainly northeast and east of the area during late
afternoon and early evening hours.

For the rest of southern Nevada, northwest Arizona and southeast
California...Mainly looking for typical diurnal wind trends through
Sunday. Isolated storms will be possible across mainly Mohave County
and eastern Lincoln County this afternoon and evening with slight
chances for thunderstorms becoming a little more widespread Sunday.

&&

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

SHORT TERM//FIRE WEATHER...Outler
LONG TERM....Wolcott/Outler
AVIATION...Harrison

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