Severe Thunderstorm Warning 17, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
842 AM PDT Mon Sep 23 2019

.SYNOPSIS...A vigorous low pressure system dropping into
southern Nevada today will bring increasing chances for showers and
thunderstorms today especially over northwest Arizona where
extensive heavy rainfall and flash flooding are possible this
afternoon and tonight. The low pressure system will park near Yuma
Arizona the next few days then lift away as a deep broad area of low
pressure develops over the western states this weekend leading to
widespread gusty winds and a significant cooling trend.
&&

.UPDATE...Ingredients coming together rapidly for a rather active
day in Arizona. Moisture currently working its way northward, with
surface dewpoints and PWATs rising rapidly in southern Mohave
county. Wind shear, moisture, and steepening lapse rates will
support strong to severe thunderstorms in southern Mohave county.
Flooding is possible with training of storms. The best chances
look to be roughly south of Kingman, but recent high-res trends
show secondary activity popping up around Boulder City and Lake
Mead this evening - with the Las Vegas valley on the fringe, but
not out of the woods.
&&

.DISCUSSION...Today through next Monday.

An active weather pattern is shaping up today which will provide
thunderstorms over northwest Arizona with the potential for heavy
rain. Isolated large hail and damaging winds possible with a few
storms. A Flash Flood Watch has been issued for central and southern
Mohave County from 11 AM this morning through late tonight. Nearby
areas of far southern Nevada and southeast California will see
isolated thunderstorms, but the primary focus will be in northwest
Arizona.

The evolving scenario includes fairly deep moisture that has been
slowly moving up from northwest Mexico and will be pulled up fairly
quickly over the southern half of Mohave County this morning ahead
of a vigorous closed low that will spin directly into southern
Nevada by this afternoon and then over Yuma Arizona late tonight.
The cyclogenesis associated with the closed low will provide both
dynamic upward forcing and increasing wind shear to support training
and organized storms over central and southern Mohave County from
late this morning through late this evening. As the closed low
center moves down the Colorado River Valley toward Yuma tonight,
storms may develop under the cold pool then pull south of Lake
Havasu after midnight.

The cutoff low is now forecast to remain quasi-stationary around
Yuma through Wednesday then slowly lift toward Kingman Thursday
which will increase the chances of another round of showers and
thunderstorms Wednesday into Thursday.

The ensemble models indicate the broad upstream trough over the
northwest states will finally dig and encompass the entire western
states Friday through next weekend which will produce breezy and
progressively cooler conditions through the weekend and early next
week with temperatures trending well below normal.
&&

.AVIATION...For McCarran...Light, south to southwest winds beneath
a periods of scattered to broken at or above 20 kft will continue
through 18z. Winds will stay southerly as they increase this
afternoon, with gusts reaching 25 knots at times. The late afternoon
and evening forecast will be tricky. A cold front is expected to
push 10-12 kt northwest winds, scattered clouds at or above 10 kft,
and vicinity showers into the valley between 01-04z. Meanwhile,
easterly outflow may be possible in the same general timeframe,
which may override the frontal winds. That said, forecast confidence
this evening is low. Expect variable winds overnight tonight,
favoring a northwest to west direction and lingering scattered mid-
level clouds.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds will give way to 10-15 kt south to
southwest winds at each TAF site with the exception of KBIH. A cold
front will usher in north winds this afternoon at KBIH and advance
further south into southern Nevada and southeast California this
evening. T-storms will focus across the lower Colorado river and NW
Arizona areas today; starting as early as 16z. CIGs dropping to 5-7
kft, strong winds and hail will be possible with some storms; storm
activity will wane around 03-06z. While storms will be generally
confined to NW Arizona, showers will be possible anywhere south of I-
15. Generally, north winds around 7-12 kts along with scattered CIGs
at or above 10kft are expected overnight.
&&

.SPOTTER INFORMATION STATEMENT...A Flash Flood Watch is in
effect for central and southern Mohave County Arizona from 11 AM MST
this morning until late tonight. Spotter activation for Mohave
County is likely. Elsewhere in nearby southern Nevada and southeast
California, spotters are encouraged to report any significant
weather or impacts according to standard operating procedures.
&&

UPDATE.......Steele
DISCUSSION...Adair
AVIATION.....Boothe

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

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LAS VEGAS NV
1248 PM PDT MON SEP 23 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1243 PM     HAIL             1 NNE DESERT HILLS      34.56N 114.36W
09/23/2019  E1.00 INCH       MOHAVE             AZ   TRAINED SPOTTER

            TRAINED SPOTTER REPORTED QUARTER-SIZED HAIL.
            ON THE NORTH SIDE OF LAKE HAVASU CITY NEAR
            THE AIRPORT.

&&

CFS