Hail in Nevada, October 21, 2018

Area Forecast Discussion
National Weather Service Las Vegas NV
849 PM PDT Sat Oct 20 2018

.UPDATE...
Updated to the forecast this evening to account for the expected
development of showers and isolated thunderstorms tonight. This
included just a few minor adjustment to coverage and intensity of
precipitation. The short-range CAM guidance has been remarkable
consistent with the development of showers and isolated
thunderstorms overnight. The HRRR brings this activity up from
the south near Phoenix as it pushed across the Las Vegas area and
heads northward tward tomorrow morning. The new run of the
SPC/SSEO also shows a similar set up. All this seems legit given
the forcing from the upper low moving inland from the Pacific. The
afternoon sounding here at Vegas indicated an eroding cap at
around 600mb which is likely the primary inhibition for activity
thus far. What does this all mean? Basically, we expect that
activity will begin to develop shortly for southern, central and
eastern portions of our CWA. Things appear on track thus far.
&&

.PREV DISCUSSION... /issued at 115 PM PDT Sat Oct 20 2018/

.SYNOPSIS...Increasing shower and thunderstorm activity is expected
tonight across mainly southern Nevada and Northwest Arizona as a low
pressure system approaches the area. Residual activity will linger
into Sunday before drier and more stable air pushes in Monday.
Improving conditions are expected next week with dry conditions and
a warming trend on the way.

&&

.SHORT TERM...through Monday night.

While conditions across the region remain dry at this hour, change
is already underway with moisture advection on the increase.
Afternoon visible satellite imagery depicts cloud streets across the
Mojave desert and an increasing cumulus field across eastern Mohave
county.  MDCRS samples from aircraft in the region suggest a
moderate capping inversion remains in place this afternoon around
600mb, which will continue to limit the vertical extent of cloud
development until later this evening when mid-level cooling begins
to increase as stronger ascent moves in. As such, I kept PoPs fairly
low through 8pm tonight, and then began ramping them up as shower
and thunderstorm activity increases across Mohave county and lifts
northwest into Clark and southern Lincoln counties. It looks like
best window for the Las Vegas Valley will be between 11pm and 6 am
for shower activity, through recent model trends suggest the most
favored area tonight may be across the eastern half of Clark county.

The main threats from shower and storm activity tonight will be
brief heavy rain and associated wet and slick roadways.  Some minor
flooding is possible, but swift northward motion should limit that
risk for most areas unless more persistent banding features develop.
Fairly strong deep layer shear will also promote the potential for
some small hail with the stronger thunderstorm cores.

On Sunday, the main focus areas of precipitation will lift into
Lincoln county in the morning, but additional shower and storm
activity will likely break out in the afternoon thanks to cool
temperatures aloft and surface heating of a fairly moisture rich
boundary layer. Brief heavy rain and small hail will again be
possible.

Drier conditions will move in Monday as the trough pushes inland. A
few terrain driven showers will remain possible across Lincoln and
Mohave counties, but should be isolated to scattered at best.

.LONG TERM...Tuesday through Saturday.

High pressure ridge will build in during the long term period, with
heights risings dramatically Thursday into Friday as the high builds
over the southwest.  This will lead to an extended dry period with
temperatures climbing above normal. Nudged temperatures upward, but
they may still be a tad on the cool side given the strength of the
developing ridge.

&&

.AVIATION...For McCarran...Winds will remain north-northeast for
much of the day with speeds 7-9 kts. By late afternoon, winds will
become light and variable lasting through the overnight hours and
into Sunday. Clouds will continue to increase today around 8 kft. By
6Z tonight, showers will pop up in the vicinity of the terminal and
last through Sunday afternoon.

For the rest of southern Nevada, northwest Arizona and southeast
California...Gusty north winds are expected along the Colorado River
Valley, particularly at the KIFP TAF site, with gusts up to 25-30
kts possible. Elsewhere, winds will be light through the forecast
period. Clouds will continue to increase through the day today.
Showers will be in the vicinity of the terminals around 6Z at all
sites but KBIH. Higher terrain will be obscured at times.

&&

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

&&

Update...Lericos
SHORT TERM/LONG TERM...Outler
AVIATION...Varian

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