Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 190936

Area Forecast Discussion
National Weather Service Las Vegas NV
240 AM PDT Mon Mar 19 2018

.SYNOPSIS...Benign weather conditions are expected today with
increasing clouds and precipitation chances in the Sierra by
Tuesday.  Rain chances will spread eastward Wednesday and Thursday,
with the potential for locally heavy rainfall across parts of the
Mojave Desert and Southern Great Basin.  The warm nature of this
weather system will limit snow accumulations to the very highest
elevations of the Sierra and Spring Mountains.


.SHORT TERM...through Tuesday night

Weak high pressure ridge will build across the region today allowing
for a slight warm up in temperatures this afternoon and overall
"nice" conditions for mid March.  Despite the slight warm up,
temperatures will still hover several degrees below daily normals
for most areas. Mid and high clouds will begin to increase once
again from the west this evening and will continue to fill into
Tuesday morning. These clouds will signal the first attempts to
juice up our atmosphere as a plume of deep tropical moisture
becomes aimed at the Southern California Coast.

Some of our higher resolution models suggest some light
precipitation may break out across the Sierra as early as Tuesday
morning, spreading across the mountains of Inyo and Western San
Bernardino County by Tuesday afternoon. I suspect much of this will
be fighting considerable dry air in the lower levels initially, but
nonetheless, added some slight chances Tuesday to much of the above
mentioned areas to account for the light rain potential.  Widespread
cloud cover is likely elsewhere. Moisture advection will continue
into the night, and maintained slight chances for rain across most
of Inyo and Western SB county, with likely chances across the
Sierra. Snow levels will be on the rise Tuesday into Tuesday night,
rising to above 8500 feet by early Wednesday morning.

.LONG TERM...Wednesday through Monday.


An AR with tropical Pacific origins (aka Pineapple Express) teams up
with another Pacific NW trough to bring ample moisture and precip
chances across the region mid to late week.

Models are now in better agreement on the timing and location of
both the AR and upper low through Thursday. With more consistency
amongst the latest models, confidence with this system has increased
a bit and widespread stratiform rain is becoming likely during the
WED-THU time frame with best chances occuring THU morning-afternoon.
Because of the tropical natural of the moisture source, snow levels
will increase to 8500`-9000` by Wednesday morning, limiting snow
accumulations to the highest elevations mostly above 9000 ft.

Main impacts with this next system are precip accumulations and
winds. Storm total QPF over the course of 2-3 days has about 0.3-
0.6" across most deserts and valleys. As the event approaches, QPF
values may increase with potentially higher amounts of 1"-2"
possible by THU afternoon. Total snow amounts over the same time
period have 2"-4" on the highest elevations of the Spring Mountains
and up to 20-50" on the eastern Sierra crest. Gusty southerly winds
begin to pick up late Wednesday afternoon and early evening as an
approaching shortwave/piece of energy from the upper low moves into
California. Strongest winds will push through Thursday with breezy
conditions sticking around through Friday then more relaxed winds
Saturday as the piece of energy moves east and weakens. Increased
cloud cover will accompany the deep moisture plume through Thursday
before returning to partly cloud skies Friday. Beyond Friday, models
diverge and confidence remains low on the evolution of the
approaching upper trough. Temperatures hover around normal through
much of the week.

Climate comparison: If all the ingredients come together, this event
may be comparable to the significant AR event that occured in our
forecast area on December 19th-22nd, 2010. During this event, up to
2"-6"  of rain fell across most desert and valley locations and 25"-
70" of snow fell on the higher elevation mountains. Extensive
damaging impacts occurred during this event. With a very similar
synoptic set-up, equivalent impacts may occur with the upcoming


.AVIATION...For McCarran...Fair conditions expected today with light
winds following diurnal trends expected through the TAF period.
Increasing high clouds are expected tonight, becoming BKN-OVC mainly
above 20k, with CIGs decreasing to 10-15k Tuesday.

For the rest of southern Nevada, northwest Arizona and southeast
California...Fair conditions expected across the region today with
light winds favoring diurnal trends. BKN-OVC skies will return
tonight mainly above 20k, with CIGs decreasing to 10-15k Tuesday and
some shower activity likely near the Sierra, with virga possible


.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.  Rainfall and flooding reports are encouraged during
periods of weather later this week. &&


LONG TERM...Kryston

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