334
FXUS65 KFGZ 181956
AFDFGZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
1256 PM MST Tue Aug 18 2026

.SYNOPSIS...Temperatures warm up to 5 to 10 degrees above average
throughout the week. Low grade monsoon conditions continue today
with only isolated storms over the White Mountains. By midweek,
thunderstorm coverage begins to increase across the area as
additional monsoon moisture is drawn across the state. A bit
cooler temperatures arriver for the weekend.

&&

.DISCUSSION...The axis of high pressure aloft extended from over
Arizona eastward into Texas Tuesday afternoon. Over the coming
week high pressure aloft will gradually consolidate and wobble
from over Arizona across the Four Corners eventually landing over
the New Mexico/Texas border. The high position will initially
deliver high temperatures 5 to 10 degrees above average but as the
high shifts eastward the door will open to an active monsoon
weather pattern.

For Wednesday...The center of high pressure aloft will become
focused over Arizona. The result will be downright hot weather at
mid- to lower-elevations. However, every location in northern
Arizona, including the mountains, will range from 5-10 degrees
warmer than average. For this reason, an Extreme Heat Warning is
in effect for elevations below 4000 feet in the Grand Canyon
through Thursday. Monsoon moisture begin it`s upward trend (partly
due to outflow from thunderstorms over northwest Mexico Tuesday
night/Wednesday morning) with isolated to scattered showers and
thunderstorm anticipated midday and afternoon over the Mogollon
Rim and White Mountains then locations southward guided by
northeast flow around the high.

From Thursday into early next week...As the high shifts eastward
the door opens to active monsoon weather. The primary reasons for
the moisture increase will be enhanced low-level flow from over
the Gulf of California and and easier path for thunderstorm
outflow over northwest Mexico and southeast Arizona to spread
across the state. In addition, with high center moving eastward
subsidence aloft will weaken putting an end to the
capping/stabilizing layer aloft. On Thursday, as the high becomes
established over the Four Corners look for scattered to numerous
showers and thunderstorms area wide, most numerous from the
Mogollon Rim/White Mountains to the Grand Canyon and Kaibab
Plateau. For Friday and over the coming weekend full monsoon
activity is forecast with scattered to numerous showers and
thunderstorms across the area likely lasting well into the
overnight hours. Otherwise, temperatures cooling to seasonal
averages by Thursday or Friday with a light wind environment
continuing.

&&

.AVIATION...Tuesday 18/18Z through Wednesday 19/18Z...VFR conditions,
brief MVFR near showers/storms. Scattered showers/storms in the
White Mountains, with isolated showers/storms possible over the
Rim through 02Z. Daytime winds SW-W at 5-10kts, light and and
variable or terrain driven overnight. Gusty and erratic winds
possible near storms.

OUTLOOK...Wednesday 19/18Z through Friday 21/18Z...VFR conditions,
brief MVFR near showers/storms. Isolated to scattered showers/storms
over Rim and White Mountains Wednesday between 18Z-03Z. Scattered
showers/storms Thursday starting on the high terrain and spreading
into lower elevations by late afternoon/early evening. Winds SW-W
5-15kts daytime Wednesday, W-NW at 5-15kts daytime Thursday,
light and variable or terrain driven overnight. Gusty and erratic
winds possible near storms.

&&

.FIRE WEATHER...Wednesday and Thursday...Temperatures rise to 5-10
degrees above average. Expect isolated to scattered showers and
thunderstorms each day with the best coverage over the eastern
Mogollon Rim and White Mountains. Winds SW-W at 5-10 mph Wednesday
and W-NW at 5-15 mph Thursday. Gusty and erratic winds possible near
storms. Minimum RH values 10-15% over the lower deserts to 30-35% in
the White Mountains.

Friday through Sunday...Temperatures around 5 degrees above average
Friday, cooling to near normal over the weekend. Scattered showers
and thunderstorms increasing in coverage each day with most of the
area seeing a chance for shower/storms by the weekend. Winds S-SW
at 5-15 mph. Gusty and erratic winds possible near storms.

&&

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

&&

$$

PUBLIC...McCollum
AVIATION...Zanker
FIRE WEATHER...Zanker

For Northern Arizona weather information visit
weather.gov/flagstaff