990
FXUS65 KFGZ 201846
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1146 AM MST Sun Sep 20 2026

.SYNOPSIS...Dry and seasonable weather is expected today before
moisture returns Monday, bringing increasing chances for showers
and thunderstorms. More widespread precipitation is expected
Tuesday, along with breezy southerly winds. Uncertainty increases
Wednesday onward, but daily shower and thunderstorm chances remain
in the forecast through the work week.

&&

.DISCUSSION...Northern Arizona is currently under the influence of
a short-wave ridge induced by a West Coast low centered off the
coast of north/central California. Water vapor satellite imagery
shows that very dry low and mid-level air has overtaken the region.
Preciptable Water (PW), a measure of atmospheric moisture, has
dropped to between 0.25-0.50 inches. For comparison, PW values
yesterday morning ranged from 0.35-0.75 inches. Model soundings
indicate the atmosphere is too dry and stable for shower or
thunderstorm development today, and the forecast calls for dry
weather across the area. Otherwise, expect increasing high cloud
cover associated with the West Coast low, light surface winds and
near-normal high temperatures.

On Monday, model forecasts are in good agreement that the West
Coast low will begin to influence northern Arizona`s weather as
it moves inland across central California. High resolution model
guidance has become increasingly confident that the area will see
a return of shower and thunderstorm development beginning as
early as Monday afternoon, especially in the northwest around
Grand Canyon Country. The current forecast calls for a 30-50%
chance for showers and thunderstorms in the northwest, with a
10-25% chance along the Mogollon Rim and White Mountains.

On Tuesday, the low lifts to the northwest. As it does so,
increasing atmospheric moisture and forcing associated with the
low will bring more widespread shower and thunderstorm
development, with the best potential for precipitation occurring
from the Mogollon Rim northward. In addition, southerly wind
speeds are forecast to increase, but are expected to remain below
Wind Advisory thresholds, with gusts near 30 mph forecast over
higher terrain. According to the high-resolution model guidance,
chances for rain rates exceeding 0.5 inches in 3 hours are
minimal, indicating a low risk of flash flooding on Monday and
Tuesday.

Model spread increases significantly beginning Wednesday,
indicating decreasing confidence in the evolution of the longer-
term weather pattern late next week. This is due to uncertainty
regarding interactions between a deep Gulf of Alaska low, the
potential development of a closed low somewhere off the coast of
northern Baja, and activity in the tropical eastern Pacific. It is
difficult to say exactly how these features will interact, so the
current forecast maintains chances for showers and thunderstorms
each day through the remainder of the work week.

&&

.AVIATION...Sunday 20/18Z through Monday 21/18Z...VFR conditions.
Winds are SW-W 5-15 kts through 02Z, then light and VRB or
terrain driven overnight.

OUTLOOK...Monday 21/18Z through Wednesday 23/18Z...Primarily VFR
conditions. ISOLD-SCT SHRA/-TSRA returns Monday evening with the
best coverage across northern Coconino county. SCT-NMRS SHRA/-TSRA
across Navajo and Apache counties on Tuesday, ISOLD elsewhere.
Winds are S-SW 10-15 kts gusting to 20 kts Monday, increasing to
10-20 kts gusting to 25 kts on Tuesday.

&&

.FIRE WEATHER...Monday and Tuesday...Showers and thunderstorms
returning late Monday. Best chances are across northwest AZ on
Monday evening/night, then across eastern AZ on Tuesday. Winds are
south through southwest 10-15 mph on Monday, increasing to 10-20 mph
gusting to 25 mph on Tuesday.

Wednesday through Friday...Chances for showers and thunderstorms
continue each day, declining slightly on Friday. The best chances
will be seen across eastern Arizona each day. Winds are generally
light each day, trending southeast through east on Wednesday and
Thursday then southwest on Friday.

&&

.FGZ WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

PUBLIC...RR
AVIATION...Peterson
FIRE WEATHER...Lewandowski

For Northern Arizona weather information visit
weather.gov/flagstaff

NWS Flagstaff Office