905
FXUS65 KFGZ 291949
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1249 PM MST Sat Aug 29 2026

.SYNOPSIS...Numerous to widespread showers and thunderstorms are
expected each day through Monday, including overnight activity.
With deep monsoonal moisture in place, heavy rainfall will be
possible with any stronger stronger storm, potentially leading to
flash flooding. Precipitation chances then begin to decrease near
the middle of next week, along with gradually warming
temperatures.

&&

.DISCUSSION...Today...Overnight convection across far northern
Arizona is giving way to clearing skies across the remainder of
the region. Given this trend, daytime heating looks to be able to
maximize destabilization over the area later today. 14Z RAP
guidance shows a large area of 1000-2000 J/Kg of MLCAPE forecast
from areas Coconino and Yavapai counties. At the same time, the
approaching trough from the west will increase vertical wind shear
across the area, especially to the north. 0-6 km shear values of
around 20-30 kts look probable across western and far northern
Arizona. As a result, strong to severe thunderstorms are expected
to develop this afternoon across northern Arizona, with the best
chances being over Coconino and Yavapai counties. The main threat
with any severe storm will be large hail, however some damaging
wind gusts will be possible over the lower elevations.

Deep monsoonal moisture is also in place across the region, with
PWATs around an inch in the Four Corners region, increasing to
around 1.5 inches south of the Mogollon Rim. Therefore, flash
flooding will remain a possibility this afternoon (in addition to
the severe threat). The only limiting factor for flash flooding
looks to be 15-25 kt storm motions, though the likelihood of training
storms will likely negate this factor.

Tonight...Following today`s convection across southern Arizona, an
MCS looks to move northward out of the Lower Deserts into northern
Arizona late this evening. While the severe threat will diminish
with the loss of daytime heating, the flash flood potential will
begin to ramp up. Latest U of A WRF guidance shows the complex
moving up through the Phoenix metro into Yavapai and Gila counties
after 8-9 PM MST, then lifting northeast as it begins to decay
through the rest of the overnight hours.

12Z HREF PMM of >= 1" of rain in 3 hours signals towards the
greatest risk areas for flash flooding overnight being across
Yavapai and Gila counties. For this reason, a Flash Flood Watch is
in effect through the overnight hours.

Sunday and Monday...Monsoonal moisture looks to remain in place
through Monday, along with the dynamics of the approaching trough.
Given this, a repeat of Saturday looks likely on Sunday and
potentially again on Monday. Therefore, severe weather will remain a
threat during the afternoon hours, then transitioning to an
overnight flash flood risk as a decaying MCS moves northward out of
the Lower Deserts. Guidance from the U of A WRF signals towards
potentially more widespread nocturnal activity Sunday night into
Monday morning. HREF PMMs show an even higher signal for heavy
rainfall across central Arizona late Sunday evening into Monday
morning. For this reason, an additional Flash Flood Watch has been
issued for all of northern and central Arizona.

The limiting favor for all of this each day will be any remnant
debris clouds. Given the increased nocturnal activity, daytime
heating may be limited during the morning hours. This could
potentially result in delayed convective initiation and/or reduced
coverage.

Tuesday through Friday...A fast-moving trough looks to move through
Great Basin near the middle of next week. This looks to initially
suppress monsoonal moisture further south, with much of the GEFS, EPS,
and CMCE member showing a sharp decline in PWATs for the middle of
next week. Operational guidance seems to have trended further
westward with Tropical Storm Karina, thereby limiting the northward
push of the sub-tropical moisture surge along Baja California.

However, with another tropical system potentially developing behind
Karina and troughing remaining over the west, an increase in
moisture later in the week remains a possibility. GEFS, EPS, and
CMCE members remain split on continuing with the downward trend, or
increasing PWATs potentially as early as Thursday/Friday. Therefore,
uncertainty remains high near the end of the forecast package as the
exact timing and track of the both the trough and potential tropical
cyclone are crucial.

The operational guidance does have heights tick upwards slightly, so
a slight warming trend seems likely, but overall we look to remain
seasonable to slightly cooler than normal temperature wise into next
week.

&&

.AVIATION...Saturday 29/18Z through Sunday 30/18Z...SHRA/TSRA
expected at times through the TAF period. Highest coverage through
06Z, then concentrated mainly along/south of KPRC-KFLG-KRQE
06Z-14Z. MVFR/IFR conditions likely in heavier showers/storms.
Outside of gusty storm driven winds that could reach near 40 kts,
look for W-SW winds 10-20 kts. Light/variable winds forecast
overnight.

OUTLOOK...Sunday 30/18Z through Tuesday 01/18Z...SHRA/TSRA
expected at times through the TAF period. Greatest coverage will
be between 18Z-02Z, but expect activity to persist overnight as
well, especially Sunday night into Monday morning. MVFR/IFR
conditions likely in heavier showers/storms. Outside of gusty
storm driven winds that could reach near 40 kts, look for south
through west winds 10-20 kts. Light/variable winds forecast
overnight.

&&

.FIRE WEATHER...This afternoon through Monday...Scattered to
widespread showers and thunderstorms expected. Greatest coverage
forecast for the afternoon hours, but activity expected to
persist overnight as well. Localized heavy rain may lead to flash
flooding, especially over burn scars. Outside of gusty/erratic winds
around/in storms, look for southwest winds 10-20 mph each afternoon,
variable 10 mph or less overnight.

Tuesday through Thursday...Shower and thunderstorm activity
decreases to isolated to scattered coverage. Outside of
gusty/erratic winds around/in storms, look for southwest winds 5-15
mph each afternoon, becoming variable overnight.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Sunday afternoon through Monday evening for
AZZ004>018-037>040.

Flood Watch from 5 PM MST this afternoon through late tonight
for AZZ008-018-037-038.

&&

$$

PUBLIC...Humphreys
AVIATION...JJ
FIRE WEATHER...JJ

For Northern Arizona weather information visit
weather.gov/flagstaff