Flash Flood and Damaging Winds in Arizona, September 2 to 5, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
201 PM PDT Sat Sep 2 2017

.SYNOPSIS...Isolated shower and thunderstorm activity is expected
to develop late this afternoon through this evening, especially
over central Mohave County into the Colorado River Valley. Chances
for storms will spread to the rest of the region Sunday as
moisture overspreads the area. Storm chances will decrease in
most areas Monday as high pressure begins to build. However,
storms may continue each afternoon as low-grade monsoon moisture
is recycled each day.
&&

.SHORT TERM...Through Monday.

The Gulf Surge that came up the Colorado River Valley earlier
today has all but stopped between Lake Mohave and Lake Mead this
afternoon. To the south, dew points in the 60's were present along
the river, with upper 40s and 50s elsewhere south of I-15. This
low-level moisture will provide a decent environment for storms to
propagate west into the area from the Mogollon Rim. Though the
latest HRRR runs have decreased in strength, there are still
indications that a cold-pool driven complex could push into Mohave
County to the Colorado River Valley late this afternoon and this
evening. If this does occur, gusty (potentially severe) winds
will be the primary concern. Additional showers (possibly virga)
will then be possible overnight in an arch from Kingman to the
Spring Mountains, to Owens Lake overnight as the leading edge of
the moisture boundary (associated with remnants from TS Lidia)
pushes north across the region.

For Sunday, ample moisture will be in place for isolated to
scattered storms. Storms will be most likely over the high terrain
across the region, with little more than diurnal heating creating
lift.

Moisture will be to wane on Monday as high pressure begins to
build over the region. However, storm chances will continue
across the high terrain of the southern Great Basin and Mojave
Desert with moisture trapped under the ridge.

.LONG TERM...Tuesday through Friday.

The medium range models indicate a possible transition to a fairly
deep trough by next weekend, especially the ECMWF solution.
Meanwhile, an amplified ridge is forecast to be over the western
states Tuesday while a closed slow spins off the central California
Coast. This will provide hot conditions with temperatures several
degrees above normal. In addition, the east to southeast flow
between the two circulations will persist through Wednesday over our
forecast area and allow some moisture to be drawn up from Arizona
leading to chances for afternoon and evening thunderstorms,
particularly over the higher terrain. A deep trough extending from
the Pacific Northwest to central California then comes into the
picture Thursday and is forecast to progress inland late Thursday
through Saturday. The ECMWF digs it down over southern California
Saturday as a closed low while the GFS keeps it over northern Nevada
and Utah as a more open wave. Confidence in the details is low for
next weekend and we will need to watch for increasing shear Thursday
and Friday combined with any lingering moisture which can lead to
more organized thunderstorms. Temperatures will be on the decline
and will be almost cool (at night) next weekend if the ECMWF comes
close to verifying.
&&

.AVIATION...For McCarran...Winds should remain less than 10 kts
favoring an easterly to southeasterly direction through most of the
afternoon. By 22-23Z today, winds should favor a south to
southeasterly direction with winds increasing to around 10-12 kts.
Occasional gusts are possible this evening up to around 15 kts.
Isolated to scattered thunderstorms are possible in the Peach
Springs and Daggett corridors later this afternoon into the
overnight period. With highest chances in the Peach Springs
corridor. There exists a slight to moderate chance of outflow winds
reaching the terminal today between 02-05Z and would likely cause
stronger gusts around 20-30kts from the south or southeast. SCT to
BKN above 14kft through the forecast period.

For the rest of southern Nevada, northwest Arizona and southeast
California... Isolated to scattered thunderstorms are possible
across northwest Arizona, far southern Nevada, and eastern San
Bernardino County this afternoon and evening, with highest chances
across the Colorado River Valley and central Mohave County. Gusty
outflow winds will be the primary concern with any thunderstorm
activity that develops this afternoon and evening. SCT to BKN above
14kft through the forecast period with cigs down to 10kft at times.
The rest of the region will see generally light diurnal winds with
FEW to SCT above 14kft.
&&

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

SHORT TERM...Wolcott
LONG TERM....Adair
AVIATION.....Kryston

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