099 
FXUS65 KVEF 180313 AAB
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
813 PM PDT Mon Jul 17 2017

.SYNOPSIS...A moist and unstable airmass will result in scattered to 
numerous thunderstorms and locally heavy rainfall across southern 
Nevada...Northwest Arizona...and far eastern California through the 
week. Drier conditions are expected across most of Inyo county where 
temperatures will remain hot and skies remaining mostly sunny. 
Slight drying is advertised by the end of the week but isolated 
thunderstorm activity will remain possible across the region. 

&&

.UPDATE...Cancelled Flash Flood Watch for Las Vegas, Spring Mtns, 
Sheep Range and southern Clark County. Radar detecting scattered 
storms over northeast Clark County while storms continue to weaken 
over Mohave County so Flash Flood Watch remains in effect.  
&&


.PREV DISCUSSION...130 PM PDT Mon Jul 17 2017
.SHORT TERM...thru Wednesday Night.

Active evening expected with scattered to numerous thunderstorms 
developing across southern Nevada and Northwest Arizona. Instability 
across the region is impressive and favorable conditions will be in 
place for both very heavy rainfall and damaging microbursts winds. 
The ongoing flash flood watch looks good, and will need to watch for 
pulse severe storm potential through the remainder of the day.  This 
coincides well with the SPC Day 1 outlook, highlighting a marginal 
risk of severe storms, and the WPC outlook suggesting an elevated 
flash flood threat.  Storms today will most likely fire along the 
higher terrain of Clark and Mohave counties and gradually propagate 
into the hot and unstable lower deserts through the afternoon and 
evening, perhaps congealing into a complex that dives south towards 
the Colorado River valley. 

Conditions tomorrow will moisten further, with precipitable water of 
1.0-1.5" or greater lifting north across much of eastern Mojave 
desert and into Lincoln county. Considered a flash flood watch but 
Im concerned about cloud cover limiting destabilization early in the 
day, especially from I-40 south. With some doubts on the amount of 
sunshine and instability that can be realized, held off an extension 
of the watch until we have greater confidence in the threat. The 
midnight shift can take a closer look tonight.

Moisture will linger Wednesday as well, with continued potential for 
strong storms and heavy rainfall assuming cloud cover doesn't limit 
heating too much.  Temperatures the next several days will be 
trending downward as clouds and shower/storm chances trend upward. 


.LONG TERM...Thursday through Monday.

The latest GFS and ECMWF solutions indicate monsoonal moisture will 
be fairly substantial over southern Nevada and surrounding areas 
Thursday then trend downward for the weekend with less fuel for 
thunderstorms. A light southerly flow forecast over the region 
Thursday will keep in place substantial monsoonal moisture with Pwat 
values of 1.25-1.50" over Clark, eastern San Bernardino, Mohave and 
southeast Lincoln counties. Chances for thunderstorms will be 
similar to Wednesday and those moisture levels will provide the 
potential for some heavy rain producing storms. A drying southwest 
flow is then forecast Friday into Saturday as an eastern Pacific 
trough moves inland. Behind it Sunday and Monday, high pressure is 
forecast to lift up from Baja across southern California and over 
Nevada while an inverted trough moves west across Sonora and the 
Gulf of California. This may lead to another upswing in moisture 
after Monday, but thunderstorm chances were reduced a little Sunday 
and Monday.

&&

.AVIATION...For McCarran...Very uncertain forecast for tonight and 
much of the week as thunderstorms will be the main concern. There 
are three possible scenarios this evening and tonight. The first 
scenario, with roughly a 30 percent chance of occurrence, is for 
thunderstorms to affect the terminal. If this occurs, the main 
threats will be very heavy rain and erratically shifting gusty 
winds, and the most likely time of occurrence would be between 2 PM 
and midnight. The second scenario, with roughly a 50 percent chance 
of occurrence, is for thunderstorms not to affect the terminal 
directly, but affect the approach corridors and cause erratic 
shifting winds at the terminal due to one or more outflow 
boundaries. If this occurs, outflow winds would most likely come 
from the south, east, or north, and the most likely time of 
occurrence would be between 3 PM and 3 AM. The third scenario, with 
roughly a 20 percent chance of occurrence, is for thunderstorms not 
to affect the terminal directly or via outflow boundary. If this 
occurs, winds would remain from a southerly direction at about 10 
knots with occasional gusts of 15 to 20 knots. Most clouds would be 
above 10K ft, except for one to perhaps two oktas of cumulonimbus 
with lower bases.

For the rest of southern Nevada, southeast California, and northwest 
Arizona...Scattered thunderstorms will persist through the evening, 
with the greatest coverage in Mohave, Lincoln, eastern Nye, Clark, 
and eastern San Bernardino Counties. The main threats will be very 
heavy rain and low ceilings in Mohave, Clark, southern Lincoln, and 
eastern San Bernardino Counties, and erratic gusty winds and blowing 
dust in eastern Nye and northern Lincoln Counties. Showers and 
thunderstorms could persist in Mohave County all night. Away from 
thunderstorm influences, winds will be mainly south to southwest at 
10 to 20 mph.


&&

.FIRE WEATHER...Increasing moisture is expected through Wednesday 
across the region with scattered to numerous thunderstorms expected 
across Southern Nevada and Northwest Arizona. Lesser activity is 
expected across eastern California, with generally dry conditions 
for most of Inyo county expected through the week.  Daily rain 
chances and increased cloud cover can be expected further east along 
with improved relative humidity values which will hold though 
midweek before declining gradually as we approach the weekend. 

&&

.HYDROLOGY...Creeks, streams and rivers in northern Inyo County 
continue to run high and fast from snow melt. 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. Isolated thunderstorms over the mountains may aid snowmelt 
runoff and keep some drainages elevated over the coming days as 
well. 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.
&&

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

$$

Update...Pierce

SHORT TERM/FIRE WEATHER...Outler
LONG TERM...Adair
AVIATION...Morgan

For more forecast information...see us on our webpage:

http://weather.gov/lasvegas or follow us on Facebook and Twitter