904
FXUS65 KFGZ 210800
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
100 AM MST Thu Aug 21 2025

.SYNOPSIS...Chances for showers and thunderstorms rise over the
coming days as monsoonal moisture begins to increase over northern
Arizona. Scattered to widespread storms, some with heavy rain and
localized flash flooding, are expected to develop by weeks end
and continue into next week. Hot temperatures will remain through
Friday, before cooler temperatures return for the weekend.

&&

.DISCUSSION...Today...An increase in shower and thunderstorm
activity is expected later today as strong ridge of high pressure
over the Four Corners continues to advect monsoonal moisture
northward into Arizona. Surface dewpoints across northern Arizona
have all largely risen to near 40-50F with the increase in
moisture, and even some closer to 55-60F south of the Mogollon
Rim.

As a result, another round of scattered showers and thunderstorms
are expected to develop later today. Given the current steering
flow, storms look to initially develop along the higher terrain
(Mogollon Rim, Black Mesa, and the Chuska Mountains) this afternoon.
Storm will then eventually move southwest off the terrain into the
lower elevations in the late afternoon and early evening hours. The
strongest storms will likely be across Yavapai and Gila counties,
where deeper moisture and better instability will be present. The
main threats with these storms will initially be heavy downpours
leading to localized flash flooding, however, gusty winds may become
a threat later as outflows develop across central Arizona late in
the afternoon.

Outside of the storms, hot temperatures are expected across much of
northern Arizona (at least where storms don`t develop early). Highs
this afternoon look to be in the mid 80s F to low 90s F in the
higher terrain to the 100s F and even some flirting with 110F in the
warmer desert locations. However, temperatures in the higher terrain
where storms develop early this afternoon may see slightly cooler
highs. An Extreme Heat Warning remains in effect for the lower
elevations of the Grand Canyon.

Friday onward...Heights start to fall as the ridge begins to weaken.
As this occurs, the subsidence inversion aloft begins to weaken as
well, allowing for a bit more vigorous convective development going
into the end of the week and early next week. As a result, numerous
to widespread showers and thunderstorms are expected each day. Given
the abundant moisture, flash flooding will be the primary threat,
especially over recent burn scars. A few stronger storms may also
potentially produce hail and gusty winds.

Coverage on any given day will largely be dependent upon any remnant
mesoscale features (outflows and lingering debris clouds) from the
previous day and any potential overnight convection. These features
are largely not that predictable beyond 24 hours. The pattern in
place would largely suggest more of the same, with storms forming
over the higher terrain in the afternoon and moving southwest into
the lower deserts by the evening hours. As the high begins to shift,
this will begin then start to shift the focus along and north of the
Mogollon Rim.

Ensemble guidance from the EPS, GEFS, and CMCE all still favor a
continued increase in moisture. Thus, this active monsoon pattern
looks to hang around through at least the middle of next week. Most
of the guidance does seem to favor this weekend as the peak in
moisture, before the high gradually begins to shift eastward next
week.

With the falling heights, cooler temperatures look to set in by the
weekend and early next week. Afternoon highs this weekend look to be
more seasonable for this time of year, with highs by the middle of
next week potentially around 5F below normal.


&&

.AVIATION...Thursday 21/06Z through Friday 22/06Z...Mainly VFR
conditions expected through the TAF period. Brief MVFR conditions
possible near SHRA/TSRA, but only very isolated activity remains
overnight. Outside of storm driven outflow winds, look for light
and variable winds. Additional SHRA/TSRA expected after 18Z
Thursday, mostly along and south of a KPGA-KRQE line.

OUTLOOK...Friday 22/06Z through Sunday 24/06Z...Daily chances for
showers/storms will continue each afternoon/evening. Main hazards
will be heavy rain, small hail, gusty/erratic winds, and
lightning. Outside of storm development, look for VFR conditions
and winds 10 kts or less varying in direction.

&&

.FIRE WEATHER...Today Friday...Hot conditions continue. More
widespread showers and thunderstorms expected on today and Friday,
along with increasing RH values. Winds generally variable 5-10 mph.
Gusty and erratic winds possible in and around thunderstorms.

Saturday through Monday...Increasing chances for numerous to
widespread showers and thunderstorms with wetting rains each day.
Winds will primarily be variable 5-10 mph. Gusty and erratic winds
possible in and around thunderstorms.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Extreme Heat Warning until 8 PM MST Friday for AZZ006.

&&

$$

PUBLIC...Humphreys
AVIATION...Konieczny
FIRE WEATHER...Humphreys

For Northern Arizona weather information visit
weather.gov/flagstaff