Flash Flood in California, April 8, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
300 AM PDT Wed Apr 8 2020

.SYNOPSIS...An area of low pressure off the the southern
California coast will finally move inland today. The low will then
wobble over southern California and southern Nevada through Friday
night before finally moving east across Arizona Saturday. The storm
will bring periods of moderate to heavy rainfall associated with
embedded thunderstorms; primarily to southeast California today.
Significant mountain snow continues in the southern Sierra Nevada
with lighter amounts for the southern Nevada mountains. Isolated to
scattered light showers will linger through Friday. Another quick
hitting system will bring a slight chance of showers to southeast
Nevada and northwest Arizona Sunday into Monday.

&&

.SHORT TERM...through Friday night.

Changes:

Downgraded the Winter Storm Warning to a Winter Weather Advisory for
the Spring Mtns/Sheep Range. Extended duration through 5 pm Thursday
afternoon.

Winter Storm Warning for the eastern Sierra Slopes extended until 11
am Thursday.

NEW: Winter Weather Advisory issued for Esmeralda/central Nye
Counties in Nevada and the White Mountains in Inyo County through 11
am Thursday morning.

No Change to Flash Flood Watch.

Currently, upper low is spinning off the southern California coast.
Moisture plume is feeding into San Diego County then moving
northward across the western Mojave Desert and into the southern
Sierra Nevada and Owens Valley. Have seen rain rates up to 0.20"/hr
for 1 hour along the foothills of the southern Sierra Nevada around
midnight. Otherwise, rain rates have been 0.10"/hr or less.

The anomalously deep low is forecast to move into coastal southern
California by late this afternoon. HRRR/HREF both depict new areas
of showers and later in the day thunderstorms developing in eastern
California and moving northward across San Bernardino County/lower
Colorado River Valley. The north/south orientation of the current
precipitation band will take on a more northwest-southeast
orientation across San Bernardino County by late afternoon. Still
looking at lighter precipitation developing north of this area
across southern Nevada this afternoon. As the upper low oscillates
over the region on Thursday a favorable easterly upslope flow will
continue into the southern Sierra through Thursday morning. That
easterly flow will also bring accumulating snow to the White
Mountains of Inyo County, as well as the higher terrain of Esmeralda
and central Nye Counties. Forecast for the Spring Mountains/Sheep
Range remains more challenging. So far, warm temperatures have
limited the amount of new accumulation in Kyle Canyon. Lee Canyon
has done better. Yesterday and again today, guidance has backed off
on total accumulations for the remainder of this event through
Thursday. So, with lower accumulations downgraded the warning to a
winter weather advisory. The threat for light showers continues
through Friday mainly for southeast California and northwest Arizona
Friday.

.LONG TERM...Saturday through Tuesday.

An upstream shortwave finally nudges the low east on Saturday away
from the area. That upstream system is forecast to clip eastern
Nevada/northern Arizona Sunday/Monday which should be bring a slight
chance of showers along a cold front, some gusty winds and cooler
temperatures.

&&

.AVIATION...For McCarran...Impacts to the terminal this afternoon
include showers and isolated thunderstorms, low ceilings and gusty
winds. Rain showers could develop over the Las Vegas Valley as early
as 21Z, with the highest chances from 23Z-3Z, with showers in the
vicinity of the terminal possible through the night. Ceilings should
drop to around 8 kft through the morning, with CIGs as low as 2-3
kft possible with shower activity. As the freezing level drops below
7 kft, there may be periods of light icing this afternoon. Winds
will be light and variable through the early morning hours before
southeasterly gusts pick up late-morning to 25 kts through sunset.
As the afternoon progresses, directional variability increases. Wind
direction could vary from 170 to 230. Additionally, erratic isolated
wind gusts exceeding 30 kts possible if a nearby thunderstorm kicks
off an outflow.

For the rest of southern Nevada, northwest Arizona and southeast
California...Rain showers and isolated thunderstorms possible today
for all TAF sites, with chances spreading into the Las Vegas Valley
and Colorado River Valley TAF sites late-morning to early-afternoon
and lasting through the evening. CIGs will generally be around 8
kft, with ceilings as low as 2-3 kft with shower development. Drops
in the freezing level could result in periods of light icing this
afternoon. Winds will be generally light through the morning, though
south-southeasterly wind gusts will pick up across northwestern
Arizona and southern Nevada around 18Z and last through sunset.
Though, through the afternoon, wind direction will become more
southwesterly. Erratic isolated wind gusts exceeding 30 kts possible
if a nearby thunderstorm kicks off an outflow.

&&

.CLIMATE...
A late-season storm could break daily precipitation records
across the region.

DAILY RECORD RAINFALL TOTALS

               WED 4/8      THU 4/9
Las Vegas, NV  0.28 (1943)  0.81 (2016)
Bishop, CA     0.21 (2016)  0.71 (2016)
Barstow, CA    0.34 (2016)  0.43 (1975)
Needles, CA    0.67 (2016)  0.13 (1978)
Kingman, AZ    0.48 (2016)  0.71 (1965)

&&

.SPOTTER INFORMATION STATEMENT...An unusually potent late-season
storm system is bringing abundant desert rain and mountain snow
to the region through Friday. Embedded thunderstorms are possible
especially Wednesday afternoon and evening. Spotter activation is
not anticipated at this time, but spotters are encouraged to
report any precipitation amounts and rain, snow or wind related
impacts according to standard operating procedures.
&&

DISCUSSION...Pierce
AVIATION...Varian

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