Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 231650

Area Forecast Discussion
National Weather Service Flagstaff AZ
950 AM MST Sun Jul 23 2017

.SYNOPSIS...A Flash Flood Watch has been issued for northern
Arizona valid Sunday from noon to midnight. Heavy rainfall with
flash flooding is possible from stronger storms. Active monsoon
conditions are expected to continue Tuesday. A decrease in storm
coverage should develop starting Wednesday, especially across
western and central Arizona.


We have issued flash flood watch for for all of Apache, Coconino,
Navajo, Yavapai, and northern Gila Counties valid from noon today
through midnight tonight. The cloud cover and light rain showers
that covered southern Coconino and Yavapai counties at sunrise is
decreasing, and cu development is already going south of the
Mogollon rim and over the San Franciso peaks. PW in this mornings
sounding is over an inch, with mositure increase seen in the
700-550 mb layer vs 24 hours ago. We have seen a few observed 2
inch reports from yesterday,  and expect more today given what
we`ve seen this morning.


.PREV DISCUSSION /414 AM MST/...Expecting an active day as
abundant monsoon moisture is present over central and northern
Arizona. Model forecast soundings indicate fairly high levels of
instability along and south of the Mogollon Rim this afternoon,
with steering flow generally pushing storms slowly toward the
west/northwest. This setup would allow for a few strong to
marginally severe thunderstorms developing along the Mogollon
Rim/White Mtns and pushing slowly into northern Gila and portions
of Yavapai County later in the afternoon and evening. Also, with
the stronger storms (and/or areas with cell training), there will
be a risk of heavy rain and localized flash flooding. One thing
that could limit this possibility is ongoing cloud cover, acting
to inhibit instability and storm strength. If these clouds show a
decreasing trend later this morning, there could be a need for a
Flash Flood Watch for this  afternoon/evening from the Mogollon
Rim southward - we will monitor through the morning. Later
tonight and inverted trough feature over southeast AZ
is forecast to move up into northern Arizona, with abundant
moisture persisting. This will turn the steering flow from the
southeast tonight and then southerly Monday. Storms could persist
into the overnight hours tonight with the help of the feature. On
Monday, forecast soundings show a nearly saturated atmosphere
through a deep layer. Rain chances are high, but the amount of
cloud cover could act to hold down instability and decrease storm
intensity, rainfall rates and flash flood potential. Stay tuned as
this part of the forecast remains uncertain and could change.

Tuesday - the inverted trough is forecast to move north of the
state, with slightly lower precipitable water values over the
region. Looking for a more typical monsoon pattern, with scattered
afternoon storms moving SW to NE.

Wednesday & Thursday - models indicating a drier air mass and
some warming in the mid levels. Not expecting storms to shut down
completely, but coverage should be isolated to scattered at best.

Friday onward - high pressure forecast to shift to our north,
allowing for easterly flow and gradual moistening. Storm chances
return to typical monsoon levels.


.AVIATION...For the 18Z package...Sct to numrs shra/tsra and isold
+tsra. Most storms forming over higher terrain and moving west and
northwest. Activity will be slow to decrease tonight, transitioning
to more of a stratiform type. MVFR/IFR conditions in the strongest
storms. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Expect above normal storm activity and high relative
humidity values Sunday and Monday, as moisture continues to stream
into the district. Wetting rain chances will remain high.

Tuesday through Thursday...Chances for showers and thunderstorms
will continue, but coverage and frequency should decrease. Slightly
drier conditions near the surface will enhance the threat for gusty
outflow winds, associated with thunderstorms.


.FGZ WATCHES/WARNINGS/ADVISORIES...Flash Flood Watch through this evening FOR AZZ004>018-037>040.




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