Flash Flood Warning 128, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1041 AM MST Sat Aug 25 2018

.SYNOPSIS...Deep monsoon moisture will bring another round of
numerous showers and thunderstorms today, with scattered storms
continuing Sunday. Drier air moving into the region will lead to
a significant downturn in shower and thunderstorm activity through
much of next week with most areas remaining dry.

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.UPDATE...A mesoscale circulation centered east of Payson this
morning is bringing an area of rain and thunderstorms to northern
Gila, SE Coconino and southern Navajo counties this morning.
Copious moisture is leading to some localized pockets of heavy
rainfall, with a spotter report of 1.00" of rain in 15 minutes at
Forest Lakes. The circulation is moving slowly toward the
northwest. Elsewhere, instability is increasing with daytime
heating. Storms are already developing near the San Francisco
Peaks, just east of Prescott, and over the northeast AZ mountains.
This morning's sounding at Bellemont showed little change in the
air mass over the area, with perhaps a bit more instability due to
cooler mid levels - in other words, look for another active day of
storms. Main threat will be locally heavy rainfall and flash
flooding, though gusty wind and hail are also likely with the
stronger storms. Forecasts updated to increase storm chances
today. Also raised Sunday afternoon's rain chances after getting a
look at new model runs this morning. Updates sent.

&&

.PREV DISCUSSION /452 AM MST/...A meso-scale circulation over east
central Arizona is triggering showers and thunderstorms over
southern Apache, southern Navajo, and northern Gila Counties this
morning. Meso scale model shows this area of storms continuing
and expanding northwestward through the day. Expect an active day
across much of northern Arizona today.

A trough of low pressure moving into the Pacific Northwest has
gradually pushed monsoon moisture over the southern Great Basin
eastward over the last two days. The boundary of 0.5 inch PW air
has now moved into far southeastern Nevada this morning. This
drier air will continue to push southeastward over the next
several days and will result in a significant downturn in shower
and thunderstorm activity Sunday through much of next week. Some
isolated storms are possible in the White Mountains with dry
conditions expected elsewhere through at least Thursday.

A cut off low may form off the southern coast of California while
a high center develops over the Southeastern States late next
week. this would bring a return of deep moisture over Arizona.
However, confidence is low that this pattern would develop.

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.AVIATION...For the 18Z package...An area of steady shra/+shra
and embedded tsra from KPAN-KSOW will persist through 18Z-19Z and
will then slowly dissipate. Localized MVFR conditions exist in this
region. Otherwise, expect sct-nmrs shra/tsra and isold +tsra to
develop aft 18Z-19Z in other areas, but especially along and SW of a
line from KFLG-KINW-KRQE. Brief MVFR/IFR in the heavier showers,
Winds generally light. Conditions becmg VFR aft 01Z-02Z. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Monsoon moisture will remain in place today, with
scattered to numerous thunderstorms developing. Greatest coverage is
expected along over Yavapai county, northern Gila county, southern
Coconino county and southern Navajo and Apache counties. Drier air
moving into the region will slowly reduce thunderstorm chances on
Sunday.

Monday through Wednesday...A drier airmass will bring mostly sunny
skies to the district, with afternoon fair weather cumulus, mainly
over higher terrain. Temperatures will be near normal for late
August.

&&

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

&&

PUBLIC...JJ/MAS
AVIATION...Peterson
FIRE WEATHER...Peterson

For Northern Arizona weather information visit
weather.gov/flagstaff