255
FXUS65 KTWC 181615
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
915 AM MST Fri Sep 18 2026

.SYNOPSIS...There will be a slight chance of showers and
thunderstorms along the Arizona/New Mexico state line and in the
White Mountains this afternoon. Otherwise, drier air will move
across Southeast Arizona over the weekend into early next week.
Moisture then spreads back across portions of Southeast Arizona
next week for a chance of showers and thunderstorms, mainly
east of Tucson. High temperatures will be near normal through
next week.

&&

.UPDATE...The upper pattern this morning is defined by a
distinct but weak shortwave over Cochise county extending into
NE Sonora Mexico, a trough over the Pacific Northwest/northern
Great Basin and a strong subtropical ridge spread out over the
entire southeast U.S.. Although surface dewpoints across the
valleys of Southeast Arizona range from the upper 50s to mid 60s
this morning, expect to see those values dip through the day
into the 50s as a drier southwest flow develops across the area.
It is possible that there is enough moisture and lift associated
with that weak disturbance tracking thru Cochise to kick off a
weak storm along the AZ/NM border and more specifically the
Chiricahua mountains early this afternoon, but based on the
track of the feature, these areas may be in the wake/subsident
side once there is enough instability to support thunderstorm
development. Otherwise, current forecast looks on track.

&&

.PREV DISCUSSION (issued 117 AM MST Fri Sep 18 2026)...

On the large scale, an upper low was centered along the
Nevada/Oregon state line, with a trough axis extending southward
through California and high pressure aloft was centered over
far eastern Texas. The upper low will move slowly east into
western Wyoming by late Saturday, with the trough axis sliding
across the Great Basin and northern Arizona. A secondary low
moves into the central California coast late Sunday into Monday.
This secondary low will then lift northeast through the
intermountain west early to mid next week, as high pressure
aloft shifts westward into far southern Texas.

Satellite layer blended total precipitable water imagery indicates
PWATs were currently in the 1.0"-1.2" range across southeast
Arizona, with lower values of 0.50"-0.75" to our west across
southern California and northern Baja. This drier air will begin to
move into the region from the west today as the upper low and trough
axis shift eastward. There will still be enough moisture for a
slight chance of showers and thunderstorms along the New Mexico
state line and in the White Mountains this afternoon/evening.
Modeled PWATs indicate values lowering to near 0.75" by early this
evening.

Saturday looks to be the `driest` day with model PW values around
0.50" across the forecast area and Arizona on the back side of the
aforementioned trough axis. By Sunday, model PW values start to
increase back to near 0.75" as the secondary upper low moves into
the California coast and deeper moisture starts working back
northward through eastern Sonora. While the forecast across
southeast Arizona remains dry on Sunday, we will have to monitor any
convective outflow boundaries over Sonora which may push convection
northward along the International Border in Cochise County.

By early to mid next week the low lifts across the Intermountain
West and the upper high begins to shift westward back across Texas,
and increasing amounts of moisture move back into southeast Arizona
from the east and south. The latest POP grids show a slight chance
of showers and thunderstorms across Cochise County on Monday, with a
slight chance/chance of showers and thunderstorms mainly east of
Tucson on Tuesday and then a chance of showers and thunderstorms
from Tucson eastward Wednesday through Friday of next week. Modeled
PW values by mid to late next week are back up into the 1.0"-1.25"
range across southeast Arizona.

Otherwise, high temperatures through next Friday are within a degree
or two of normal, with highs in the mid 90s in the Tucson metro, to
near 100 degrees across the western deserts and in the mid 80s to
lower 90s across the valley locations of Santa Cruz, Cochise, Graham
and southern Greenlee counties.

&&

.AVIATION... Valid thru 19/12z. Mainly clear skies/SKC conditions
west of KTUS thru the forecast period. From KTUS eastward, FEW-
SCT clouds at 8k-11k ft AGL and SCT (locally BKN clouds) AOA 20k
ft AGL between 18/17Z and 19/04Z. A slight chance of
-TSRA/-SHRA along the New Mexico state line and in the White
Mountains between 19/19Z and 20/03Z. SFC wind less than 12 kts
thru the forecast period, favoring a SWLY/WLY direction during
the afternoon/early evening hours and variable in direction at
other times. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...There will be a slight chance of showers and
thunderstorms along the Arizona/New Mexico state line and in the
White Mountains this afternoon. Otherwise, mainly dry conditions
into Monday. Moisture then spreads back across portions of
southeast Arizona next week for a chance of showers and
thunderstorms, mainly east of Tucson. High temperatures will be
near normal through next week. Min RH values will be in the
12-17 percent range west of Tucson through the weekend and 17-27
percent in valley locations east of Tucson (25-40 percent in
the mountains). RH values then increase 7-15+ percent next week
as moisture moves back into southeast Arizona. 20-foot wind will
be less than 15 mph into at least the middle of next week.
Gusty and erratic winds will accompany any thunderstorms.

&&

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

&&

$$

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