Flood in Arizona, September 7, 2016

Area Forecast Discussion
National Weather Service Phoenix AZ
832 AM MST WED SEP 7 2016

.SYNOPSIS...
Deep tropical moisture from hurricane Newton will spread across
central and eastern Arizona today and into the evening hours leading
to widespread showers, some with heavy rain, across areas to the
east of Phoenix. Isolated thunderstorms are also possible. Scattered
showers and thunderstorms will extend westward to around the lower
Colorado River valley today. Newton will move east and out of the
picture later tonight allowing drier air to slowly filter into the
area from the west. By Friday showers or thunderstorms will be
confined to higher terrain areas east of Phoenix. Starting Saturday
and continuing into early next week, monsoon moisture will again
spread into south central Arizona from the south/southwest leading
to a persistent slight chance of afternoon showers and thunderstorms
each day. Mostly sunny skies are expected over the far western
Arizona and southeast California deserts however.

&&

.DISCUSSION...
Tropical Storm Newton continues moving steadily through northern
Sonora this morning with precipitation extending northward into AZ.
Latest Phoenix sounding registered a PWAT of 1.99 inches, which is
the third highest value ever recorded in September. At the surface,
conditions are also quite humid with widespread dewpoints in the
lower 70s.

An outer rain band from Newton moved through portions of southern
Maricopa County this morning, generally producing between a half of
an inch and one inch of rain. The highest rain total observed so far
has been 1.30 inches near Gila Bend. Latest runs of the HRRR continue
to show this band gradually dissipating this morning. Focus will then
shift to the east as light to moderate rain moves northeastward from
southeastern Arizona into Pinal and southern Gila Counties. A Flood
Watch remains in effect for these areas through this evening. Some
adjustments will be made to the forecast this morning, mainly to
refine PoP/QPF/Temperatures.

&&

.PREVIOUS DISCUSSION...
Newton is forecast to reach Arizona as a Tropical Storm and
eventually weaken to depression status as it moves northeast across
southeast Arizona and approaches the New Mexican border near midnight
at a position pretty much due east of Globe. It still appears that
most of the really significant deep tropical moisture will track
across areas well to the southeast of Phoenix and the most
significant flooding issues will stay in Tucson's domain, but rain in
excess of 1 inch are still very possible across southern Gila County
today, sufficient to lead to flooding or flash flooding issues. We
will continue the Flash Flood Watch for AZZ024 and AZZ028 through 11
pm tonight although confidence in flooding is moderate at this time.

It is nice to see that operational runs from the GFS and ECMWF as
well as most of the GEFS ensemble members have locked in on the
timing and track of Newton so confidence in its movement and where
the primary rains will fall are high. Most likely the lower central
deserts will stay out of the heavier rains; most rainfall totals in
the greater Phoenix area should stay below one half inch. After
midnight tonight, what is left of Newton will continue to push east
and into New Mexico, leaving a more subsident northwest flow aloft to
overspread much of western and central Arizona; this flow will work
to thin out the moisture and as such we are looking at just slight
chances for showers/storms from Phoenix westward during the morning
hours on Thursday.

Drier southwest flow aloft will dominate the weather across
southeast California and Arizona on Friday, leading to mostly sunny
skies over the deserts and warmer high temperatures. The high
temperature in Phoenix Friday is forecast to climb back to the
triple digits with 100 degrees forecast - just barely below seasonal
normal. There may be sufficient lingering moisture over the higher
terrain east of Phoenix to allow isolated afternoon thunderstorms to
form however.

For Saturday into the early part of next week, upper troffing
gradually develops to the west of Phoenix, and the combination of
the southwest flow associated with the trof and flow circulating
around an upper high to our east will allow monsoonal moisture to
spread across portions of south central Arizona. We are not looking
a significant precipitation in the extended period, but will likely
see slight chances for afternoon and early evening storms across
south central Arizona each day with better chances over the higher
terrain east of Phoenix. The far western AZ and southeast CA deserts
should pretty much remain mostly sunny each day with high
temperatures in the triple digits.

&&

.AVIATION...

South-Central Arizona Including KPHX, KIWA, and KSDL:

Although the circulation center of the remains of hurricane Newton
is still expected to pass well to the south and east of the PHX area
terminals (over extreme SE AZ), cloudiness and showers associated
with this system are still expected to impact the greater Phoenix
area. BKN-OVC cigs in the 8-12 kt foot range, with FEW-SCT layers as
low as 4k foot are expected to prevail through the daytime hours
today before beginning to slowly lift/clear this evening/tonight as
the remains of Newton move off to the east. Scattered shower
activity is forecast to spread into the PHX area during the mid-late
morning hours, with showers becoming more numerous during the midday-
early afternoon hours, when the remains of Newton make their closest
approach, with the shower activity diminishing this evening. Winds
are expected to remain easterly through the taf period, except for a
period of more southerly winds at KPHX and KSDL late this
afternoon/early this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: The
effects of Hurricane Newton (centered over the east coast of
southern Baja Mexico as of 04Z) will primarily be east of southwest
Arizona. However, scattered cumulus and BKN-OVC clouds AOA FL120 can
be expected along with a slight chance of showers this
afternoon/early evening (mainly near and east of the Lower Colorado
River Valley). Southeasterly winds will predominate at KIPL and
southerly winds at KBLH through the taf period.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...

Friday through Tuesday...

Weak high pressure building into the region from the west is
expected to limit convective activity to just some isolated
showers/storms over the higher terrain east of Phoenix on Friday and
Saturday, and allow temperatures to recover to near, or slightly
above normal values. Another upper trof approaching from the west
will then bring slight chances for showers and thunderstorms to the
lower deserts of South-Central AZ from Sunday into next Tuesday,
with temperatures remaining near normal. Minimum humidities are
expected to remain in the 15-30 percent range through the entire
period, with good-excellent overnight recoveries. Winds to remain
mainly on the light side, except near thunderstorms.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch until 8 PM MST this evening for AZZ024-028.

CA...None.
&&

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DISCUSSION...Hirsch
PREVIOUS DISCUSSION...CB
AVIATION...Percha
FIRE WEATHER...Percha