Flash Flood Watch 2, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
345 AM PST Tue Feb 12 2019

.SYNOPSIS...There will be a slight warm up on today under
increasing high clouds. Moisture associated with our next system
will reach the southern Sierra Nevada tonight. The moisture will
continue to stream eastward across the region Wednesday and Thursday
with good chances of mountain snow and valley rain. Additional
storms systems over the weekend will keep the region cooler than
normal along with a threat of rain and snow showers.
&&

.SHORT TERM...through Wednesday night.

Morning satellite shows mostly clear skies across the Intermountain
West with high clouds lurking off to our west. Features of interest
this morning are the cold trough digging south well off the Pacific
Northwest coast and extensive plume of tropical moisture well west
of southern California across the eastern Pacific.

While high clouds increase throughout the day over the Great Basin
and Mojave Desert. The cold trough over the northeast Pacific will
tap into that tropical moisture plume, advecting moisture
northeastward. The moisture will be lifted ahead of the cold front
leading to a narrow band of high QPF across western Oregon today. As
the trough slowly sags southward the main moisture feed will sag
south into northern California tonight. There will be some light
snow breaking out along the eastern Sierra Slopes of Inyo County
late tonight. On Wednesday, models show no organized impulses to add
additional lift to the moisture streaming inland. So, we will be
counting on warm air advection and especially orographics to wring
out the moisture. The southern Sierra Nevada barrier will do a fine
job of that with a decent amount of rain/snow forecast to spill over
the crest and into the Owens Valley Wednesday and Wednesday night.
The pattern continues into the long term so we have issued a Winter
Storm Warning above 7000 feet from 4 am Wednesday morning-4 am
Friday morning. At elevations between 7-9 kft, total accumulations
will be 1-2 feet, 2+ feet above 9 kft feet. Snow levels in the Owens
Valley will initially start out around 4000 feet Tuesday night but
quickly rise to above 6500 feet by late morning Wednesday. Similar
situation around Las Vegas Wednesday morning. West Valley along the
215 Beltway may see a rain/snow mix with snow levels starting out
3500 feet before quickly lifting throughout the day. We are
forecasting the highest QPF amounts within the Owens Valley and
adjacent foothills with amounts up to 1 inch through Wednesday
night. Do expect to see a rise in creeks and streams coming out of
the Sierra. Don't expect widespread flooding concerns but won't be
surprised that an isolated creek or stream could experience minor
flooding.

.LONG TERM...Thursday through Monday.

Thursday, the area will covered by clouds with moderate moisture
from the first surge on Wednesday. A second surge of moisture should
be pulled into the Mojave Desert as shortwave energy is ejected
across the Great Basin Thursday. Additional moisture combined with
forcing should result in scattered to numerous showers across Mojave
Desert and southern Great Basin. Models indicate possible band
developing Thursday morning/afternoon along the I-15 corridor, so I
have nudged chances up slightly along I-15. Additional rain amounts
for low elevations on Thursday should fall somewhere between 0.10-
0.50", with locally higher amounts possible in eastern and western
districts of the CWA. Given the warm nature of the airmass, snow
levels will be vary between 8,000-9,000 feet, and allow for
generally minor accumulations across the northern zones and in the
Spring Mountains. Impactful snow amounts are expected in the eastern
Sierra, where an additional 6-18" snow is possible Thursday morning
through Friday afternoon. As such, a Winter Storm Warming has been
hoisted to cover the high snow amounts in the Sierra. Fairly decent
consensus that dry intrusion associated with a potent upstream upper
low will quickly clear moisture out by early Friday morning.

Through the weekend, the aforementioned upper low will rotate inland
across the PacNW. As it does, it'll increase winds and bring a
chance of showers to the eastern Sierra and northern Zones Friday
and Saturday. Strong temperature gradient suggests potential for
strong postfrontal winds Saturday. Models maintain fair agreement
through early next, resolving a series of cold shortwaves digging
southward into the Southwest.

After temperatures climb to near normal values through Friday, they
will come crashing down Sunday after a cold frontal passage and
likely remain several degrees below normal through the middle of
next week.

&&

.AVIATION...For McCarran...Light winds following mostly diurnal
trends can be expected today and tonight. Early Wednesday morning,
may see a SE-S wind developing up to 10 kts. Increasing clouds
during the period with ceiling gradually lowering to around 10 kft
early Wednesday morning.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds following mostly diurnal trends can be
expected today and tonight. Increasing clouds during the period with
ceilings gradually lowering. Southern Sierra Nevada will be obscured
by lower ceilings tonight along with mechanical turbulence in the lee
of the mountains.
&&

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

SHORT TERM/AVIATION...Pierce
LONG TERM...Boothe

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

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