829
FXUS65 KFGZ 200832
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
132 AM MST Wed Aug 20 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 early next week. Hot temperatures will remain
through Friday, before cooler temperatures return for the weekend.

&&

.DISCUSSION...Today...Hot temperatures remain today as a strong 598
dam ridge builds over the Four Corners. An Extreme Heat Warning
remains in effect for the lower elevations of the Grand Canyon
today, where highs in excess of 110F are expected. Elsewhere,
afternoon highs in the mid 80s F to low 90s F are expected in the
higher terrain and upper 90s to 100s F in the lower deserts.

Moisture does look to begin to increase sharply today, mainly from I-
17/US-89 and east. Dewpoints across eastern Arizona have already
risen to near 40-50F as outflow pushes moisture in from New Mexico.
As a result, showers and thunderstorm activity is expected to
increase later this afternoon and evening, but mainly focused over
the eastern-half of the state. The only questionable part will be
the strength of the ridge, which will likely cap any convective
development with increased subsidence aloft. Nevertheless, any
stronger storm that can develop will have the potential to produce
some gusty winds and brief heavy downpours.

Thursday and Friday...The high looks to continue to wobble around
the Four Corners region through the rest of the work week, and
remain fairly strong. Thus, hot temperatures look to continue on
Thursday and Friday for most. Their remains some question as to how
hot given the increased moisture (cloud cover), but confidence is
high enough to upgrade the watch to a warning for the Grand Canyon.
Elsewhere, temperatures look to peak at around 106-108F in lower
Yavapai and 102-104F near Page. Heat Risk highlights these areas as
major to even extreme, however this some to be more of an artifact
of our climatological highs being cooler by this point in the
summer. Thus, given our warmer/drier summer already and some
lingering uncertainty in cloud cover, additional heat headlines do
no appear warranted.

Moisture continues to increase across the area, with PWATs
approaching 0.75-0.95" in the higher terrain to around 1.20" south of
the Mogollon Rim by Thursday. Model soundings do still show some mid-
level capping in place do to the strength of the ridge, so
convective development will still be somewhat suppressed.
Nevertheless, given the increased moisture scattered storms still
look likely each afternoon. Any stronger storms will be capable of
producing heavy rain, which could lead to localized flash flooding
as well as small hail and gusty winds.

Saturday through Tuesday...A period of active monsoon conditions is
expected over the weekend and into the start of next week. Heights
begin to fall over the weekend as the ridge begins to weaken,
allowing for a return of cooler temperatures. This will also allow
for increased convective development with the cap no longer in
place, or at least not nearly as strong. Ensemble guidance from the
EPS, GEFS, and CMCE also all continue to show increased PWATs over
northern Arizona.

All and all, the best shot at monsoonal moisture so far this season
looks to be upon us. Widespread showers and thunderstorms look
possible over the weekend and potentially into the start of next
week. 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 any given day will largely be driven by the exact position
(and resulting flow) of the high, as well as remaining outflows and
debris clouds. These features are largely not that predictable
beyond 24-36 hours, so stay tuned.

&&

.AVIATION...Wednesday 20/06Z through Thursday 21/06Z...VFR
conditions expected to persist through the TAF period. Isolated
-SHRA/-TSRA possible overnight, primarily along and south of a
 KGCN-KINW-KSJN line. Light and variable winds expected through
 18Z, before winds increase to ~ 10kts but remain variable in
 direction. Winds near storms could be gusty/erratic near 25-35
 kts. Additional SHRA/TSRA possible after 18Z along and east of a
 KPRC- KPGA line.

OUTLOOK...Thursday 21/06Z through Saturday 23/06Z...VFR conditions
will persist outside MVFR conditions in heavier SHRA/TSRA. Daily
chances for showers/storms possible between 18Z-03Z, with greatest
activity likely across the higher terrain. Outside of storm
driven gusty winds, look for variable winds 5-15 kts.

&&

.FIRE WEATHER...Today and Thursday...Hot and mainly dry conditions
continue. Isolated to scattered showers and thunderstorms expected
today, most numerous across eastern AZ. More widespread showers and
thunderstorms expected on Thursday. Winds generally variable 5-10
mph. Gusty and erratic winds possible in and around thunderstorms.

Friday through Sunday...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