097
FXUS65 KTWC 171630 CCA
AFDTWC

Area Forecast Discussion...correction to update section
National Weather Service Tucson AZ
930 AM MST Fri Jul 17 2026

.UPDATE...Considerable cloud cover exits across southeast Arizona
this morning with a persistent area of light to moderate showers
across the northern part of the Tohono O`odham nation where up to a
inch of rain has fallen in the past 3 hours. Ended up issuing a
small stream advisory for that area for a couple hours with washes
likely running. Updated the remainder of the morning forecast to
remove the mention of thunderstorms this morning and reduce PoPs
across the rest of the area. A relatively down day is expected this
afternoon and evening versus yesterday. However there is weak
diffluent flow at 300 mb and with a moist atmosphere in place, the
threat of localized heavy rain and flash flooding still exits with
any thunderstorm that develops, especially for areas that were hit
pretty good yesterday. A quick look at visible imagery also showed
that a weak MCV was developing near Douglas.

&&

.SYNOPSIS...
Scattered showers and thunderstorms will again
impact Southeast Arizona this afternoon and this evening with an
elevated risk of flash flooding, especially across those areas
that received heavy rainfall Thursday. Otherwise, chances for
thunderstorms will continue through the coming week with day to
day variability in location and severity.

&&

.DISCUSSION...
The upper pattern this morning is defined by an
upper-low positioned over the SE corner of New Mexico with an
elongated upper ridge of high pressure at 300 mb across NW
Arizona into Utah and a bit farther north into WY at 500 mb.
Yesterday was quite an active day across Southeast Arizona as
the precipitable water values were moist enough to be in the
90-95 percentile of climatology. What made it active was the
modest diffluence initially at 300 mb across Cochise county
given the proximity of the upper-low to our east, followed up by
a stretching divergence across Santa Cruz into eastern Pima
county as the 300 mb high moved north during the late afternoon
into the evening. The movement of the upper high has assisted in
the MCS that has developed across central Arizona early this
morning.

Past experience has taught me that usually after a big `active`
day, the atmosphere struggles the following day because it has
been worked over and it is hard to reload. The moisture profile
will look similar today than yesterday, but what is missing is
any form of modest lift via deformation aloft for more widespread
heavy rainfall. However, given the deep moisture in place, it
wont take much for showers and thunderstorms to develop and that
can be problematic on saturated soils from those locations that
received heavy rainfall Thursday. This though is supported by
the 17/00Z HREF probability between 30-50% across ern Pima/Santa
Cruz/SW Cochise for a 3-hour rainfall in excess of an inch
within 25 miles of a point tomorrow afternoon...far less than
the probabilities we saw Thursday. So expect scattered showers
and thunderstorms today across Southeast Arizona, with the
primary threat from the storms being heavy rainfall...which
could lead to isolated flash flooding problems in areas that
received a lot of heavy rainfall yesterday.

The upper-low to the east remains quasi-stationary into the
weekend with a more favorable easterly flow developing as the
upper-ridge consolidated farther north. with the upper-low
eventually moving across Southeast Arizona along the southern
periphery Tuesday. The Monsoon season rolls-on with a ramp-up
in storms this weekend, but especially Tuesday of next week.

&&

.AVIATION /16Z FRIDAY THROUGH 16Z SATURDAY/...
Valid through 18/12Z. SCT-BKN 11-15k ft AGL thru
17/19Z, then SCT-BKN 7-10k ft AGL BKN-OVC 12-15k ft AGL with
scattered showers and thunderstorms with 3-5SM in heavy rain,
mountain obscurations, and erratic strong wind gusts of 30-40
kts possible with any storm. Outside of thunderstorms, surface
winds generally under 10 kts. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...
Daily chances for thunderstorms will continue
each afternoon and evening through the next 7 days with day to
day variability. Minimum relative humidity 25-30 percent in the
lower desert locations and above 40 percent in the mountains
this week. Winds this week will remain mainly light and under 15
mph, though strong and erratic winds will be possible with any
thunderstorm.

&&

&&

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

&&

$$

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