737
FXUS65 KTWC 190817
AFDTWC
Area Forecast Discussion
National Weather Service Tucson AZ
117 AM MST Sat Sep 19 2026
.SYNOPSIS...Drier air across southeast Arizona will continue into
Monday. Moisture then spreads back across portions of southeast
Arizona next week for a chance of showers and thunderstorms. High
temperatures will be near to slightly above normal into the middle
of next week.
&&
.DISCUSSION...On the large scale, an upper low was centered over
south central Idaho, with a trough axis extending southward through
the Great Basin into northern Arizona. Broad high pressure aloft was
centered from northeastern Mexico into far eastern Texas. The upper
low will continue to move east into the high plains early next week,
while the area of high pressure flattens out across northeast Mexico
and the southern tier of states. A secondary low then moves into the
central California coast late Sunday and shears out as it lifts to
the northeast across the Intermountain West early to mid next week.
The area of high pressure amplifies to our east mid to late next
week.
Satellite layer blended total precipitable water imagery indicates
PWATs were currently in the 0.60 to 0.80 inch range across southeast
Arizona. Drier air will continue to move into the region today as
the upper low and trough axis shift eastward. PWATs will fall into
the 0.40 to 0.65 inch range across the entire CWA today and Sunday.
This will shut down convection over the weekend.
By Monday, as the secondary low begins to move northeast through
California into Nevada and the high begins to nudge west and
amplify, flow around these two features begins to pull moisture
northward along the Arizona/New Mexico state line and areas
eastward. Although the official forecast still remains dry for
southeast Arizona on Monday, we will have to monitor any convective
outflow boundaries over Sonora which may push convection northward
along the International Border in Cochise County. PWATs increase
back into the 0.70 to 0.90 inch range Monday.
By mid/late next week the upper high amplifies to our east and flow
turns back to southerly across southeast Arizona, with increasing
amounts of moisture moving back into southeast Arizona. PWAT values
are back up into the 1.0 to 1.25 inch range across southeast Arizona.
The latest POP grids show a chance of showers/thunderstorms east of
Tucson Tuesday, from Tucson eastward Wednesday and across much of
southeast Arizona Thursday and Friday. In addition, there will be
the possibility for some tropical influences late next week. It will
come down the position/strength of the upper high on how these
features track. Still a lot of uncertainty this far out.
Otherwise, high temperatures through Tuesday are near to slightly
above normal, with highs in the mid to upper 90s in the Tucson
metro, 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. Highs then lower 2-4 degrees
mid to late next week as increasing moisture moves back into the
region.
&&
.AVIATION...Valid thru 20/12Z.
Mainly clear skies/SKC conditions from KTUS west thru the forecast
period. East of KTUS, FEW-SCT clouds at 8k-11k ft AGL. SFC wind less
than 12 kts thru the forecast period, favoring a WLY 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 across southeast Arizona into Monday.
Moisture then spreads back across portions of southeast Arizona next
week for a chance of showers and thunderstorms. High temperatures
will be within a couple of degrees of normal through next week. Min
RH values will be in the 13-20 percent range west of Tucson through
the weekend and 20-27 percent in valley locations east of Tucson (25-
40 percent in the mountains). RH values then increase 10-20+ percent
east of Tucson next week as deeper moisture moves back into the
area. 20-foot winds 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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