Flash Flooding in Arizona, September 4 to 5, 2025

Area Forecast Discussion
National Weather Service Flagstaff AZ
442 PM MST Thu Sep 4 2025

.SYNOPSIS...Plentiful monsoon moisture hangs around Arizona
through Saturday, giving fuel for scattered to numerous showers
and thunderstorms. Main hazards continue to be gusty winds,
localized flash flooding, and frequent lightning. By Sunday, drier
conditions quickly return across the state and continue through
next week.

&&

.DISCUSSION...It's becoming a rather active afternoon. Deep
monsoon moisture is being lifted by an upper level Low over
eastern Nevada and is generating numerous showers and
thunderstorms as I type this. Storm motion is dependent on
location, currently storms over the White Mountains and Chuskas
are south to north or southwest to northeast, with any storms west
of Interstate 17 moving west to east or northwest to southeast.
The storm motion will become all west to east or northwest to
southeast as the Low moves through southern Utah. Short term
models are showing an area of showers/storms moving out of
southern Utah during the overnight hours across the Kaibab Plateau
and potentially to the Interstate 40 corridor before it dies out
by morning. So will have to keep an eye on the two big fire scars
located there if this scenario pans out.

Another round of showers and storms is expected for Friday as
monsoon moisture remains in the area. Some uncertainty on the
coverage as it will be very dependent on how much the atmosphere
gets worked over from today's convection as well as the overnight
convection. Another active day is expected again on Saturday, but
by Sunday afternoon yet another west coast trough introduces dry
air again to the region and puts our Monsoon on yet another break.
So the first half of next week will be dry with the exception of
maybe an isolated storm over the highest terrain. Long term models
show the Monsoon making a return to the area by Thursday evening.

&&

.AVIATION...Friday 05/00Z through Saturday 06/00Z...VFR conditions
expected for most areas, with brief MVFR in heavier SHRA/TSRA.
Scattered SHRA/TSRA through around 04Z throughout most of the
region. There is a chance that storm activity continues overnight,
especially north of I-40, but there is low confidence in this
forecast. Expect winds around outflow boundaries 20-35 kts with
gusty and erratic winds in the immediate vicinity of SHRA/TSRA,
otherwise winds west at 5-15kts. Another round of scattered to
numerous SHRA/TSRA develops after 18Z Friday, with the highest
coverage KFLG-KSJN southward.

OUTLOOK...Saturday 06/00Z through Monday 08/00Z...VFR conditions
expected, with brief MVFR in heavier SHRA/TSRA. Expect daily
SHRA/TSRA between 18Z and 03Z each day through Saturday, with only
isolated activity on Sunday. Expect gusty and erratic winds to
20-35 kts in the vicinity of SHRA/TSRA and with outflow
boundaries, otherwise winds south to west at 5-15kts.

&&

.FIRE WEATHER...Friday and Saturday...Expect scattered to widespread
showers and thunderstorms each afternoon. Storms will be capable of
producing heavy rainfall, frequent lightning, and gusty/erratic
winds. Outside of storm driven outflow winds, look for winds W 10-20
mph. Expect minimum RH values between 30-60% on both Friday and
Saturday.

Sunday through Tuesday...A drying trend begins Sunday with
thunderstorm coverage being limited to the higher terrain of the
Mogollon Rim and White Mountains.  Only about a 10-20% chance of an
isolated storm exists on Monday as Tuesday over the White Mountains
as further drying takes place.  Expect winds W 5-15 mph through
Sunday, becoming SW 10-20 mph on Monday and Tuesday. Look for
minimum RH values between 25-45% on Sunday, 20-35% Monday, 15-35%
Tuesday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 11 PM MST this evening for AZZ008-018-037.

&&

PUBLIC...Bernhart
AVIATION...JJ
FIRE WEATHER...Bernhart

For Northern Arizona weather information visit
weather.gov/flagstaff