Area Forecast Discussion
Issued by NWS Flagstaff, AZ

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FXUS65 KFGZ 241608

Area Forecast Discussion
National Weather Service Flagstaff AZ
908 AM MST Mon Jul 24 2017

.SYNOPSIS...Widespread showers and thunderstorms are expected
across northern Arizona through this evening. Some of the storms
could produce heavy rainfall, and a Flash Flood Watch is in effect
for areas generally north of I-40. Another round of scattered
thunderstorms will develop Tuesday. A decrease in storm coverage
is anticipated starting Wednesday, especially across western and
central Arizona.


The flash flood watch for areas generally north of I-40 through
midnight looks good. Area radars show strong tstorms around the
Phoenix area this morning. Southerly flow aloft is transporting
moisture droplets from these storms northward, which has produced
a well defined line of steady stratiform rain along a line from
William-Sedona then east of I-17. This area should persist for a
few more hours, with rainfall rates of .10-.30 per hour. We did
see come clearing across southern Apache county earlier, though
now convection is starting to develop around Show Low. Scattered
showers now north of Hwy 264 will continue northward.


.PREV DISCUSSION /500 AM MST/...Deep monsoon moisture remains
entrenched over the state this morning with well above normal
precipitable water values. The inverted trough that we have been
tracking the past couple days is located over central Arizona and
is forecast to move up into northwest Arizona by this afternoon.
Widespread mainly light showers with isolated thunderstorms have
developed over the past few hours, covering much of northern and
central Arizona. As the feature slides north through the day,
expect numerous showers to continue, though cloud cover and near
moist adiabatic atmospheric profiles are expected to keep
instability down for at least the southern half of the forecast
area. Could still be a few heavy rainers, but we felt the coverage
would be more localized. Farther north, there is a better chance
for some breaks in the clouds to allow sfc heating and higher
instability. This could lead to higher rainfall rates in the
storms generally north of a Flagstaff to Window Rock line. In
coordination with NWS offices to our north, we have issued a Flash
Flood Watch from 11 AM to Midnight MST for these areas.

By Tuesday, the inverted trough feature will be north of the
state, but deep moisture will linger. Instability should be higher
than today for most areas, so a round of scattered
afternoon/evening thunderstorms is likely.

Wednesday through Thursday - some drier air enters central and
western Arizona with a decrease in storm activity. Moisture
lingers along the AZ/NM border with scattered storms.

Friday into the weekend - high pressure centered near the four
corners will result in a moistening east to southeast flow for
northern Arizona. A return to more typical monsoon storm coverage
is forecast.


.AVIATION...For the 18Z package...Many areas south of Interstate 40
are expected to see steady rainfall, along with some embedded
moderate showers. In this area, persistent MVFR conditions will
develop. North of Interstate 40, stronger storms are forecast to
develop, with brief periods of MVFR/IFR visibilities in heavy
rainfall possible. Aviation discussion not updated for TAF


.FIRE WEATHER...Expect above normal storm activity and high relative
humidity through Monday. Slightly drier and more stable conditions
arrive Tuesday, bringing activity back down to normal levels.

Wednesday through Friday...Chances for showers and thunderstorms
will continue, but coverage and frequency should decrease. Slightly
drier and warmer 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>007-009>012-




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