169
FXUS65 KTWC 121606
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
906 AM MST Sat Jul 12 2025

.SYNOPSIS...Above normal temperatures will continue through the
weekend. Expect isolated thunderstorms limited to areas near the
International Border from Nogales eastward into this evening and
along the NM border Saturday. Look for an increase in Monsoon
activity Sunday for locales east and southeast of Tucson...and
then next week for all of Southeast Arizona. As moisture and
storm chances increase next week, temperatures will drop back down
to seasonable levels.

&&

.UPDATE...

Morning visible satellite imagery shows puffs of cumulus beginning
to develop over higher terrain as surface moisture remains in
place as observed by 57-62 degree dew points at 16Z. The upper
level flow remains northwesterly however with the upper high to
the west, which will continue to usher in drier air aloft over
southeastern Arizona. GOES TPW shows precipitable water values
generally near or below 1 inch and the ALPW (advected layered
precipitable water) product shows additional mid-level dry air
advecting into the region. Additionally this pattern sustains the
subsidence that has been persistent over the previous days, which
will combine with the mid-level dry air to keep monsoon activity
on the low end today. Modest thunderstorm chances remain this
afternoon and evening over and near the higher terrain of Cochise,
Graham, and Greenlee counties.

&&

.DISCUSSION...The upper pattern this morning is defined by a stacked
ridge of high pressure centered just offshore of the California/Baja
Mexico International Border with a ridge axis extending NW-SE from
the Bight of California into northeast Sonora Mexico. The latest
GOES PWAT imagery indicated drier values of precipitable water
(0.75-0.85 inches) east of Tucson in Cochise/Graham/Greenlee
counties with another area of drier air across extreme NW Pima
county. Otherwise, we have PWAT values (0.95-1.10 inches) along
the International Border and between Tucson and Phoenix. The
combination of dry and more stable air aloft will continue to
significantly limit thunderstorm coverage again this afternoon,
with scattered showers and thunderstorms near the White
Mountains, and a slight chance of thunderstorms along the Arizona
and New Mexico border and along the International border.

We start to see the upper ridge axis shift from that NW-SE orientation
today into a more neutral orientation Sunday, allowing Southeast
Arizona to transition away from the hot and dry conditions we have
been experiencing the past several days into a more active pattern
for thunderstorms. Transition days are usually the stronger
thunderstorm days, and this looks like it will follow that
formula. As the orientation shifts Sunday, the flow at 500 mb
switches over to a divergent northwest flow with an area of
moderate stretching deformation from Tucson east. At 300 mb, we
begin to see troughiness back into the eastern CWA. Although we
still see low PWAT values across the east, we begin to see a
modest moisture advection into the area from the southeast as weak
850-700 mb trough in Chihuahua Mexico moves toward the extreme SE
corner of AZ.

What does this all mean? Well, we have a lot of ingredients for a
very active day from Tucson east with the potential for severe
thunderstorm outflow winds/blowing dust as the primary threats.
Although brief heavy rainfall will be possible with these storms,
there just isn`t enough deep moisture around yet. Storms will
build over the White Mounatins and the Gila National Forest in New
Mexico early Sunday afternoon, and drive rapidly to the southwest.
Decent mid-level flow around 20 kts will allow storms to cluster
with organized outflows developing as they track into Southeast
Arizona. The drier air aloft as well as in the sub-cloud layer
will enhance evaporation within the downdrafts...increasing the
potential for damaging winds. The 12/00Z HREF indicates a 50-90%
neighborhood (40-km) probability for wind gusts in excess of 30
kts across Graham/Cochise/Santa Cruz counties Sunday afternoon
with a 10-30% neighborhood probability of 50+ kts across eastern
Graham and Cochise counties. The big concern with these winds will
be the potential for dense blowing dust, especially originating
from the Lordsburg Playa impacting Interstate 10 in Cochise
county. The most recent model run on the Air Quality Forecast
Guidance Viewer indicates a strong plume of PM 2.5 um/m3 extending
into the SE half of Cochise county at 01Z Monday. Although the
models are mainly focusing on areas east and southeast of Tucson,
this is the type of pattern that sneaks its way into the Metro
Area. We still have a few more model runs to refine the areal
extent that will be impacted with this event.

The upper pattern continues to tilt into a more positive (NE-SW)
orientation Tuesday while the upper high continues to drift
farther west. This eventually results in a trough developing near
the Baja Spur by 00Z Wednesday. Things get intriguing Wednesday
as a weak 500 mb high over northern AZ results in a divergent NW
flow southeast of Tucson, with the upper low at 300 mb over the
northern Baja results in a diffluent S flow in the same area. The
combination of shear interacting with deeper atmospheric moisture
moving in from the south should be interesting for Southeast
Arizona.

Otherwise, the ensemble members are excited about increasing
precipitable water values 1-2 standard deviations above normal the
second half of the week into next weekend. With an upper low
wobbling around over the northern Gulf of California, this should
result in a better chance for precipitation across Southeast
Arizona. The primary threat will transition away from damaging
winds the next few days towards a threat of heavy rainfall/flash
flooding by the end of the week.

&&

.AVIATION...Valid through 13/12Z. SFC winds SLY less than 10 kts
thru 12/18Z, then WLY/NWLY 10-15 kts with gusts 20-25 kts thru
13/04Z. Stronger winds for KSAD and vicinity. SKC-SCT clouds 8-13k
ft AGL thru the valid period with isolated -SHRA/-TSRA near KDUG
between 12/20Z and 13/03Z. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Isolated thunderstorm coverage is expected to the
south and east of Tucson, mainly along the Arizona/New Mexico
border and the International Border. The main threat for storms
will be the potential for strong gusty and erratic outflow winds
40-45 mph. Otherwise, an uptick in monsoon activity is expected
beginning Sunday through next week as the upper high shifts to a
more favorable location aloft. Temperatures will remain above
normal through Monday, then drop back down to near or slightly
below normal by mid to late next week. Winds will remain westerly
from 10-15 mph, with occasional gusts at or above 25 mph, with
the exception of stronger winds in the Gila River Valley through
Saturday with northwest sustained winds around 15 to 20 mph gusts
to 30 mph. Afternoon RH values in the low lying areas will be
between 20-25%.

&&

&&

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

$$

Update...Edwards

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