Flash Flood in Nevada, March 12 to 13, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
308 PM PDT Thu Mar 12 2020

.SYNOPSIS...Slow moving low pressure off the southern California
coast will bring rain and a few thunderstorms to areas along and
southeast of a line from Death Valley to Rachel through Friday.
Heavy rain is expected for areas near and south of Las Vegas, and a
Flash Flood Watch remains in effect, along with a Winter Weather
Advisory for snow above 7500 feet in the Spring Mountains and Sheep
Range. Quiet weather is expected over the weekend before the next
storm spreads over the region Monday and Tuesday. More active
weather is likely later next week.
&&

.DISCUSSION...As of 2 PM, low pressure was centered roughly west of
Ensenada, with the heaviest rain and thunderstorms ahead of it
impacting southern California. Thus far, rain totals in our area
have topped out at a quarter inch in the Morongo Basin area.
However, two different mechanisms will come into play this evening
and overnight to bring a threat of heavy rain to areas southeast of
I-15 and perhaps a bit farther northwest. First, difluent flow
currently over the Colorado River Valley and nearby areas will keep
this area favorable for development of thunderstorms with locally
heavy rain. Although a lack of breaks in the cloud cover has kept
instability at a minimum thus far, a few breaks were noted on
visible satellite at 2 PM. Second, as the low center makes its
eastward move, the forcing driving the storms over SoCal will move
across the Mojave Desert, bringing more widespread rain to much of
the area. Rain chances will start to decrease Friday and finally end
for most of the region Friday night as the low weakens and moves
away. By this time, the next storm in the train will be deepening
off the Oregon coast, possibly providing just enough lift to keep
precip chances going from the Sierra through Lincoln County. As this
low drifts south, it could tap into moisture farther south, bringing
a chance for significant snow to the Sierra and chances for rain and
snow to much of the rest of the area. This storm looks substantially
colder than the one affecting the region now, so even though it is
mid March, lower elevation snow could still be a concern. Lots of
details left to iron out with this one, so stay tuned.
&&

.AVIATION...For McCarran...Periods of light rain can be expected
this afternoon and evening, with ceilings dropping from 8000 to 5000
feet or thereabouts. The period of lowest ceiling and visibility is
most likely to begin late this evening, continue overnight, and
possibly through much of Friday. This could be another prolonged
period of ceilings below 3000 feet, possibly as low as 1000 feet or
lower, with visibility occasionally dropping below 3 miles in rain
and mist, similar to what occurred Tuesday night and Wednesday.
Conditions should begin to improve Friday evening as south winds
increase.

For the rest of southern Nevada, northwest Arizona and southeast
California...Rain chances will increase and spread north tonight,
reaching a line from Death Valley to Rachel by morning. The main
concerns will be ceilings at or below 3000 feet, possibly as low as
1000 feet, visibility occasionally dropping below 3 miles in rain
and mist, and terrain obscuration. Conditions will begin to improve
Friday.
&&

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

Morgan

For more forecast information...see us on our webpage:
https://weather.gov/lasvegas or follow us on Facebook and Twitter