Flash Flooding and Heavy Snow in California, November 26 to 28, 2019

Area Forecast Discussion
National Weather Service Las Vegas NV
927 PM PST Tue Nov 26 2019

.SYNOPSIS...A winter storm currently gathering strength near the
Oregon coast will impact the region beginning tonight and continuing
through Friday. Significant amounts of snow and rain are expected
and will cause hazardous travel conditions heading into the
Thanksgiving holiday. The weather will be quiet and cool over the
weekend, with another round of snow possible in the Sierra Sunday
and Monday
&&

.EVENING UPDATE...Beginning to see the effects of the well
advertised system across the region in the way of heavy snow being
reported at KMMH and low clouds beginning to spread into the KBIH
terminal space. Winds are beginning to pick up as well in some of
the higher elevation ob sites in Inyo County.

Did not make any changes to PoP or QPF this evening but did bump up
wind and wind gust grids with the latest hi resolution model output.
A  few points of concern were focused on the potential for downslope
effects off the Springs as the upper level jet begins to increase
from the southwest. Another concern was the winds spreading across
southern Nevada, the Colorado River Valley, and Mohave County
tomorrow afternoon. Local model influence as well as backing in the
MET/MAV guidance, especially for KIGM tomorrow afternoon supports
bumping up winds to 20-30 mph with gusts over 40 mph at times.
Blended these trends with the afternoon forecast grids and this
resulted in portions of portions of southern Nevada and especially
Mohave County reaching advisory criteria tomorrow afternoon.
Coordinated with neighbors and agreed to coordinate the need for an
issuance on the midnight shift if trends continue.

.DISCUSSION...tonight through Friday.

Satellite water vapor imagery shows powerful low pressure system
located just off the southeast coast of Oregon with precipitation
reaching all the way south to San Francisco. The low is forecast to
move inland over southeast Oregon this evening with snow beginning
in the Sierra, coincident with the start of a Winter Storm Warning
there. Models spread precip east of the Sierra into the Owens Valley
and White Mountains overnight. Forecast snow amounts in the Sierra
tonight are 10-18 inches at Aspendell and Whitney Portal with up to
36 inches in the higher elevations. The low continues to churn over
the Pac NW on Wednesday with less intense snow in the Sierra and an
advancing precipitation line pushing east across southern Nevada and
southeast California. This is the first of two main precip bands we
will see from this system. A Winter Storm Warning goes into effect
for much of the area at 5 am Wednesday morning however, not
everywhere will see snow that early. Mohave County in northwest
Arizona, for example, will not see the onset of heavier precip until
overnight Wednesday into Thursday. It will late Wednesday afternoon
into early Wednesday evening before the any significant precip
reaches the Las Vegas Valley. The second, perhaps more significant,
precipitation shield moves across the area Thanksgiving Day and
Thursday night as the low drops south to the central California
coast. The low moves across central California Thursday night with
the cold core of the system moving across central Nevada on Friday.
More showery type precipitation is expected Friday before the system
finally flushes out completely Friday night.

Widespread low elevation forecast total rain amounts through
Saturday morning range from 0.30-1.00 inches with 1-2 inch amounts
forecast in the lower elevations of Mohave County. Total forecast
snow amounts range from 4-10 inches in Esmeralda, central Nye, and
western Lincoln counties with up to 20 inches in the higher
elevations. Eastern Lincoln County could see a wide swath of 15-25
inch snow totals along Highway 93 with 2-3 feet in northern and far
eastern Lincoln County. Total snow amounts of 1-3 feet are forecast
in the Spring Mountains with 1-2 feet in the Sheep Range, northern
Mohave County and in the Hualapai Mountains. High impact but lower
snow accumulations of 4-8 inches are possible in travel routes
including I-15 over Mountain Pass, I-40 in Mohave County, especially
east of Kingman, and 395 in the Owens Valley. Nevada State Highway
160 on the southern end of the Spring Mountains between Las Vegas
and Pahrump could see significant snow and travel impacts near
Mountain Springs. Closer into the Las Vegas Valley, Red Rock Canyon
loop could see 2 or 3 inches primarily on Thanksgiving Day with
accumulating snow within the Las Vegas Valley currently looks
limited to the far western foothills early Thursday morning. The
rest of the valley will most likely see snow showers.

Expect a brief break late Friday night into early Saturday before
the next wave (or series of waves) from the eastern Pacific brings
heavy precipitation to the West Coast. This is a warmer, moisture
laden event which could bring significant rain to California and
potentially heavy snow to the Sierra. However, model agreement is
not great and confidence is low. Keep temperatures below seasonal
norms for now through Tuesday.
&&

.AVIATION...For McCarran...Light and variable winds favoring
easterly directions will persist through the early evening before
trending more southerly late tonight. Increasing clouds are
expected, especially after 3z when sct-bkn clouds AOA 9kft will
begin moving in. Increasing southerly gusts are likely Wednesday
morning with gradually lowering CIGs to near 6k by mid afternoon.
Shower activity will be on the increase especially late in the
afternoon, with steadier rainfall likely holding off until the late
afternoon.

For the rest of southern Nevada, northwest Arizona and southeast
California...Generally light winds expected this afternoon with
increasing clouds from west to east moving in this evening.
Southerly gusts will be increasing across the Owens Valley near KBIH
after dark with CIGs lowering rapidly overnight with an approaching
weather system. CIGS below 1kft AGL likely late tonight near KBIH
with periods of light to moderate snow. Elsewhere, deteriorating
conditions will traverse from west to east Wednesday with mountain
obscurations and CIGs below 5kft AGL likely at times.

&&.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather according to standard operating procedures.
This would include significant rain and snow amounts and winds.
&&

DISCUSSION...Salmen
AVIATION...Outler

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