Lightning Strike and Heavy Rain in Nevada, May 1 to 2, 2018

Area Forecast Discussion
National Weather Service Las Vegas NV
358 AM PDT Tue May 1 2018

.SYNOPSIS...A storm system will move across the area today through
Wednesday bringing widespread rain and mountain snow showers. The
heaviest precipitation is expected in an arc extending from the
Mojave Preserve through the Spring Mountains, Lincoln County, and
into southwest UT. A few areas along the I-40 corridor will see wind
gusts of 25-35 MPH this afternoon otherwise winds are expected to
remain relatively light. Drying and warming is expected later
this week into the weekend.
&&

.SHORT TERM...Today through Wednesday Night.

As of 4 AM, light radar echoes were developing north of a line
extending from Olancha to Indian Springs, along the northern edge
of the Las Vegas Valley and across northern Mohave County. This
activity is only expected to increase through the morning, and
expand further south this afternoon. The main shortwave that will
carve out an upper low later today was located west of Los Angeles
and will round the base of the trough this afternoon and tonight.
This will be the period when the most widespread precipitation is
expected.

Significant changes were made to the forecast this morning, mainly
regarding precipitation placement today and tonight. Models are
in good agreement that the storm system will track further
southeast than previously modeled. Previous guidance had
indicated that the best chances for significant precipitation
would extend from the Sierra east across central NV, mainly just
north of Las Vegas. Now guidance has the most significant
precipitation along an arc extending from the Mojave Preserve
through the Spring Mountains, Lincoln County, and into southwest
UT. This has resulted in a reduction in QPF for Inyo and Esmeralda
counties, and therefore reduced snow accumulation for the
Sierra/White Mountains. I have opted to keep the Winter Weather
Advisory in place for now since snowfall is still likely today.
However, it's possible that the advisory could be cancelled later
today or tonight. The bigger story is the increased QPF and snow
accumulation expected for the Spring Mountains and the rest of
Clark County. QPF for the Spring Mountains is now approaching
1.5", with snowfall estimated as follows:
* Trace-4" above 6500'
* 4-10" above 8000'
* 8-14" above 9000'

Some guidance indicates even higher amounts, approaching warning
level in the high elevations. We will have to monitor the
situation closely today ands make updates as needed. Widespread
weak CAPE of 100-500 J/kg and cool upper level temperatures will
result in a fairly widespread chances of isolated embedded
thunderstorms that could produce small hail. These storms will
weaken overnight, but with the cold core overhead I cannot
completely rule out overnight convection. Again, moisture levels
are not impressive with this storm, but minor roadway ponding,
water flowing in normally dry washes, and minor flooding in
extremely sensitive areas cannot be ruled out.

The upper level low should be centered over west central Mohave
County by 12z pushing east through the day. For Wednesday,
conditions will become more showery, with most activity over the
mountains. Conditions will gradually dry out from west to east
through the day.

Temperatures will be much cooler the next couple days, with highs
dropping to around 70F in Las Vegas both days.

.LONG TERM...Thursday through Tuesday.

Strong upper low will be exiting the area Thursday will bring in
drier air to much of the area. There will be some lingering moisture
over mainly the far northeast corner of Mohave County where an
isolated shower/thunderstorm will be possible over the higher
terrain. High pressure will then move into the region Friday and
Saturday bringing a significant warming trend to the area.
Temperatures are expected to increase about 25-30 degrees from
Wednesday to Saturday. However, at this time these temperatures are
expected to remain below record levels. The ridge will flatten and
shift east Sunday as a shortwave trough moves into the west coast.
Other than some gusty southwest winds Sunday there will not be much
of an affect from this trough as temperatures will only cool
slightly. Dry conditions along with above normal temperatures will
continue through Tuesday.
&&

.AVIATION...For McCarran...South winds around 10-12 kts will
continue early this morning before becoming variable under 6 kts
after 14z. Winds are then forecast to turn more easterly late this
morning around 6-8 kts. Winds will be more tricky in the afternoon
as showers and isolated thunderstorms develop in and around the Las
Vegas Valley. Gusty and erratic winds will be possible near
showers/storms through much of the afternoon and overnight hours.
Away from any showers, winds are forecast to turn more south to
southwest after 22z and continue into this evening. Cigs down to 8k
feet will be possible and could drop even lower near showers.

For the rest of southern Nevada, northwest Arizona and southeast
California...Winds over much of the region will be 10 kts or less
expect over southern Mohave County where winds up to 20 kts will be
possible. Scattered showers and thunderstorms are expected today
across much of the area with snow levels down to 7000 feet. Gusty
and erratic winds are likely near storms and cigs down to 5-7k feet
will be possible.
&&

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

SHORT TERM...........Wolcott
LONG TERM/AVIATION...Gorelow

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