890
FXUS65 KTWC 252030
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
130 PM MST Fri Sep 25 2026

.SYNOPSIS...Dry conditions areawide on Saturday. A moisture increase
is expected from the southwest Sunday resulting in mid and high
level cloud cover and a slight chance of showers and thunderstorms.
Deep tropical moisture will then move into the area from the south
Monday and Tuesday. A low pressure system and trough moving in from
the West Coast will interact with this moisture, resulting in
widespread showers and thunderstorms. Dry conditions are then
forecast for the end of next week. High temperatures will be near to
slightly above normal over the weekend, lowering to 4-8 degrees
below normal for most of next week.

&&

.DISCUSSION...The large scale pattern has a storm system moving
across the northern tier of states and high pressure aloft centered
over the northern Gulf and lower Mississippi Valley into Saturday.
By Sunday, a trough starts to dig south along the Pacific Coast as
the center of the high shifts westward into northeast Mexico and
Hurricane Polo moves northward along Mexico to west of the Baja tip.
On Monday into early Tuesday, an area of low pressure forms over
central California within the deepening trough over California, as
Polo starts to make an eastward curve into Gulf of California south
of the Baja Spur. By Tuesday into early Wednesday, the upper low
moves from west to east across central Arizona dragging a frontal
boundary/trough axis across the state, with the remnants of Polo
tracking northeast across central Sonora and northern Chihuahua.

Drier air will continue to move into Arizona from the west through
Saturday, as the storm system pushes east across the northern tier
of states. There will be a slight chance of showers/thunderstorms
into the early evening hours tonight in northern Graham and Greenlee
counties and along the New Mexico state line, with dry conditions
elsewhere. PWATs continue to lower on Saturday down into the 0.50 to
0.75 inch range, with dry conditions areawide.

By Sunday, PWATS start to increase as the trough digs to our west
and we start to tap moisture to our south. PWATs come up into the
1.0 to 1.2 inch range by late in the day. There will be a slight
chance of showers and thunderstorms Sunday afternoon and Sunday
night.

Monday and Monday night PWATs jump up into the 1.2 to 1.6 inch range
as the trough deepens to our west and Hurricane Polo curves east
across the southern Baja Peninsula, the Gulf of California and then
makes landfall between Los Mochis and Guaymas. The flow across
southeast Arizona at this time will be southerly tapping this deep
moisture, as the upper low and associated trough begin to push in
from the west. Precipitation chances rise significantly across the
forecast area during the day Monday into the 50-60 percent range
across much of the area, with near 80 percent POPs in the White
Mountains. The highest POPs areawide occur Monday night, with values
in the 65-90 percent range.

Tuesday into early Wednesday, the upper low and trough axis will
shift eastward across the state and precipitation chances will
gradually wind down from west to east. Across western Pima County
the precipitation chances are expected to end during the afternoon
hours Tuesday and then late Tuesday night into the early morning
hours Wednesday across eastern portions of the forecast area.

Behind the upper low and trough Wednesday, there will be a slight
chance of showers and thunderstorms along the New Mexico state line,
with the rest of the forecast area remaining dry. High pressure
aloft then builds over the eastern Pacific Ocean and southeast
Arizona dries out significantly under westerly flow Thursday into
the following weekend.

Given the deep moisture across southeast Arizona Monday through
Tuesday and the strong dynamics associated with the upper low and
frontal boundary/trough axis there will likely be isolated severe
thunderstorms over this time frame, along with the potential for
flash flooding with any of the stronger thunderstorms. In fact, WPC
has already highlighted the eastern two-thirds of southeast Arizona
(roughly Sells eastward) in a slight risk of excessive rainfall for
Monday.

Otherwise, high temperatures will be near to slightly above normal
over the weekend, lowering to 4-8 degrees below normal for most of
next week.

&&

.AVIATION...Valid through 27/00Z.
FEW-SCT clouds at 9k-12k ft AGL thru 26/02Z, then clear skies/SKC
conditions thru the remainder of the forecast period. SFC wind less
than 12 kts thru the valid period and SWLY thru NWLY in direction
during the afternoon/early evening hours and variable in direction
at other times. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions areawide on Saturday. A moisture
increase is expected from the southwest Sunday resulting in mid and
high level cloud cover and a slight chance of showers and
thunderstorms. Deep tropical moisture will then move into the area
from the south Monday and Tuesday. A low pressure system and trough
moving in from the West Coast will interact with this moisture,
resulting in widespread showers and thunderstorms. Dry conditions
are then forecast for the end of next week. High temperatures will
be near to slightly above normal over the weekend, lowering to 4-8
degrees below normal for most of next week. Minimum RH values will
be in the 17-30 percent range from Tucson westward this weekend,
with values in the 27-40 percent range east of Tucson. RH values
will then increase 10-25 percent Monday and Tuesday of next week,
gradually lowering through the end of next week. 20-foot winds will
be less than 15 mph into early next week. Breezy southwest to west
winds will be possible Tuesday as a surface front associated with
the trough moves across the area. Gusty and erratic winds will be
possible with any thunderstorm that do develop.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Zell

Visit us on Facebook, X, YouTube, and at weather.gov/Tucson