Flash Flooding in Arizona, July 12, 2017

Area Forecast Discussion
National Weather Service Flagstaff AZ
923 AM MST Wed Jul 12 2017

.SYNOPSIS...Look for seasonable temperatures with afternoon and
evening showers and thunderstorms continuing well into next week.

&&

.DISCUSSION...Monsoon moisture will remain in place across
northern Arizona well into next week. Anticipate that there will
be day-to-day variations in coverage of showers and storms but
that monsoon activity will be hanging around for a while.

For today...The morning sounding at Bellemont shows that some
drying has taken place over the past 24 hours. The models indicate
that some weak sinking motion is located across northwest
Arizona. As a result, we are looking at a bit of a downturn in
storm activity along and northwest of a line from the four corners
to Payson. Southeast of this line deep moisture will remain in
place with a typical round of monsoon thunderstorms. General storm
motion is expected to be to the east/northeast (based on the flow
aloft) with tendency to form over the mountains midday and move
toward the lower elevations from the mid afternoon into the early
evening.

Over the coming week...The monsoon high shifts northward becoming
centered over the general area of Utah, Arizona and Nevada. Not much
change in thunderstorm coverage on Thursday and Friday. From
Saturday onward, the position of the high will deliver a general
northeast to east flow to northern and central Arizona. Under this
pattern activity north of the Mogollon Rim tends to be on the low
side with drier air(and that is what we are anticipating). From
the Mogollon Rim southward the door often opens up to a flow of
low-level moisture from over the Gulf of California and
thunderstorm outflows from over northwest Mexico. When the flow is
just right this deep moisture moves all the way to the Mogollon
Rim. Deeper moisture means the potential for stronger storms which
would include the Mogollon Rim country and locations south such
as Prescott, Payson and surrounding areas. We'll be keeping an eye
on this one.

&&

.AVIATION...For the 18Z package...Expect sct shra/tsra and isold
+tsra. Convection initiating over higher terrain and moving
east/northeast. Most activity will be east of a line from KPRC-KCMR-
KGCN. Brief MVFR/IFR in the stronger cells. Activity diminishing aft
00z-02z Thursday. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Slightly less activity can be expected today and
Thursday, mainly over the western and northern zones, as drier and
more stable southwest flow continues. Central and eastern zones will
remain in a medium grade monsoon pattern. Minimum relative humidity
values will drop over the northern and western zones. Winds apart
from thunderstorms will be light.

Friday through Sunday...After comparatively quiet conditions again
on Friday, the district will slowly return to a widespread medium to
high grade monsoon pattern. This is due to an easterly wave that
will push moisture back west and north over the weekend. A modest
warming trend will develop Friday and Saturday, as the ridge aloft
strengthens.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.

&&

PUBLIC...McCollum
AVIATION...MCT/Peterson

For Northern Arizona weather information visit
weather.gov/flagstaff

Hazardous Weather Outlook
National Weather Service Flagstaff AZ
420 AM MST Wed Jul 12 2017

AZZ004>018-037>040-130700-
Kaibab Plateau-Marble and Glen Canyons-Grand Canyon Country-
Coconino Plateau-Yavapai County Mountains-
Northeast Plateaus and Mesas Hwy 264 Northward-Chinle Valley-
Chuska Mountains and Defiance Plateau-
Little Colorado River Valley in Coconino County-
Little Colorado River Valley in Navajo County-
Little Colorado River Valley in Apache County-
Western Mogollon Rim-Eastern Mogollon Rim-White Mountains-
Northern Gila County-Yavapai County Valleys and Basins-
Oak Creek and Sycamore Canyons-Black Mesa Area-
Northeast Plateaus and Mesas South of Hwy 264-
420 AM MST Wed Jul 12 2017

This hazardous weather outlook is for Apache...Coconino...
Northern Gila...Navajo...and Yavapai Counties in Northern
Arizona.

.DAY ONE...Today and Tonight
Expect initial storm formation over the Mogollon Rim and White
Mountains by late this morning. Thunderstorms will be most
prevalent from the Mogollon Rim eastward, with less activity in
western Yavapai county and western Coconino county.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Expect less storm coverage through Friday, especially over the
western sections. A warming trend will develop late this week.
Moisture will become deeper and move back north and west over the
weekend, with storm activity increasing.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to standard operating procedures.

KD