Area Forecast Discussion
Issued by NWS Las Vegas, NV

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 211002

Area Forecast Discussion
National Weather Service Las Vegas NV
300 AM PDT Wed Mar 21 2018

.SYNOPSIS...Abundant cloud cover expected across the region today
with precipitation chances mainly confined areas north and west of I-
15.  Rain and high elevation snow will increase in intensity across
the same areas tonight with periods of heavy rainfall possible
across the Owens Valley. Rain spreads east across the entire region
Thursday with improving conditions expected Friday into early next


.SHORT TERM...through Thursday night.

Weak shortwave embedded in a broad and increasingly moist
southwesterly flow aided in the development of some light rain
shower activity earlier this evening, mainly across our far western
zones. Dry air in the lower levels limited precipitation amounts to
generally a trace or less, but have helped to prime the atmosphere
for more efficient precipitation accumulation ahead of a stronger
system moving in later this morning.  Snow levels overnight have
been running a little lower than anticipated, near 7,000 feet, but
will continue to rise today to near 9,000 feet with continued warm
advection ahead of a strong and moist Pacific trough.

Expect precipitation to break out once again late this morning
mainly across the Western Mojave Desert and Inyo county. By this
evening, steady rain and high mountain snow is expected in the Owens
Valley and Sierra, becoming heavy at times as very rich moisture
plume becomes aimed at the southern Sierra.  Further east, some
light showers and sprinkles are possible along the I-15 corridor
late this afternoon but amounts will be quite light due to
considerable dry air in the low levels that will first need to be
overcome. This activity will lift north into the southern Great
Basin overnight before shifting southward once again Thursday. Best
precipitation chances for the I-15 corridor and points east can be
expected as the moisture plume shifts eastward during the day

All in all, forecast remains on track. I did make some modest boosts
to QPF for most of the area as model guidance trends slightly wetter
- which makes sense given the strong IVT values aimed at the region
and highly anomalous precipitable water values in play.  The flood
watch for the Owens Valley and Sierra continue to look good and
those areas remain favored to see the greatest impacts from this
storm.  Snow levels falling on the backside of the storm system also
support the Winter Weather Advisory for elevations above 7,000 feet
in the Sierra on Thursday.  Snow levels will remain too high in the
Spring Mountains for any significant snow impacts. Precipitation
impacts for the Las Vegas area and most of the I-15 corridor will be
greatest on Thursday, with rainfall amounts of a tenth to a quarter
of an inch a good bet.

.LONG TERM...Friday through Wednesday.

By Friday, much of what is left of the moisture plume will be north
and east of the area. Models still indicate a weak shortwave will
move across the area early Friday. The GFS/ECMWF are in slightly
better agreement on the strength of this feature. Even with somewhat
limited moisture kept slight chances of showers/snow showers mainly
for eastern Lincoln County and the Arizona Strip through Friday
afternoon. A fair amount of instability will be across southern
Nevada and northwest Arizona Friday afternoon, as such decided to
put slight chance of isolated thunderstorms/thunder snow Friday

By Friday evening, dry southwest flow ahead of a broad upper low
will move over the region pushing any residual moisture eastward and
bring breezy to gusty southwest winds. Both the GFS/ECMWF have a
shortwave pushing into northern California and across the Great
Basin Saturday-Sunday, but the timing, location, and intensity of
this feature still remains uncertain. Generally, with limited
moisture the only potential impacts looks like increased SW winds
SAT and some slight chances of precip Sunday mainly north of Clark
County. Beyond Sunday afternoon confidence is low as models become
vastly different. Temperatures will be a few degrees below normal to
start off the weekend before dropping a bit more behind a cold front
Sunday. Otherwise, expect fair weather with partly cloudy to mostly
clear skies through much of the weekend and into early next week.


.AVIATION...For McCarran...Overcast conditions expected through the
TAF period with CIGs between 5-10k expected. Light showers or
sprinkles are possible late this afternoon between 21z - 03z, with
CIGS as low as 5k. Widespread clouds will linger overnight with
increasing chances for rain during the day Thursday. Light south
winds will become breezy this afternoon with gusts to 25 knots
possible out of the southwest. Winds will weaken overnight but
return Thursday with with similar velocities.

For the rest of southern Nevada, northwest Arizona and southeast
California...Widespread clouds expected through the TAF period, most
abundant north and west of I-15.  Light rain showers expected north
of a KDAG-KSGU line this afternoon and evening with CIGs falling to
between 4-8kft AGL at times.  Periods of rain, heavy at times,
expected further west near the Sierra and KBIH with IFR/LIFR
conditions possible at times.  In addition, southwesterly afternoon
winds may gust up to 20 knots this afternoon.


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


LONG TERM...Kryston

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.