Flood in Arizona, September 7, 2016

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

.UPDATE...Updated Aviation and Fire Weather Discussions.

.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...
At 3 am this morning, Tropical Storm (formerly Hurricane) Newton
continued to push to the north-northeast just inland along the
northwest Mexican Coast and the circulation center is progged by NHC
to reach Nogales by around noon today. IR imagery early this morning
continued to show copious amounts of cloud cover spreading north and
across most of Arizona, with much deeper moisture still lurking just
south of Arizona and ready to flood into mainly southeast Arizona
during the day today. Not long ago the PWAT value on the Phoenix
sounding was a record low 0.30 inches and as of yesterday evening it
had climbed to 1.2. The Tucson sounding was much more impressive
with a PWAT of 1.6 inches. 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.

For today POPs were mainly massaged as no significant alterations
were needed. Some hi-res mesoscale models did suggest that
convection will develop this morning and push westward  and into the
western deserts, possibly even reaching the lower Colorado River
Valley - and better CAPE values are present mainly west of Phoenix
today - so we did raise POPs a bit out west and into the 25-40
percent ballpark. Slight chances exist as you move into far
southeast California but by and large, the precip event associated
with Newton will be an Arizona event with a prime focus over areas
east/southeast of central Phoenix.

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 from 5 AM MST Today through This evening
     for AZZ024-028.

CA...None.
&&

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DISCUSSION...CB
AVIATION...Percha
FIRE WEATHER...Percha