636
FXUS65 KTWC 281657
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
957 AM MST Sat Jun 28 2025

.SYNOPSIS...Generally dry and warmer this weekend with only slight
chances for showers and thunderstorms near the International
Border in Cochise County. The hottest day will be Monday when an
Extreme Heat Warning is in effect for portions of Southeast
Arizona. Monsoon moisture is expected to increase next week with
increasing precipitation chances, especially the second half of
the week including Independence Day.

&&

.DISCUSSION...All is quiet across Southeast Arizona this morning
as the upper pattern is defined by a strengthening upper high
across the Desert Southwest and an upper low off the West Coast
over the Eastern Pacific. This morning the 500 mb high center is
centered over southern California/western Arizona with a general
broad ridge extending across Southeast Arizona at 300 mb. This
broad ridge will then begin to amplify Sunday and especially
Monday over Arizona as the upper low orients itself into a neutral
position and moves slowly east into California. This will allow
for thicknesses to increase, with the 850-700 mb thickness
reaching 1700m, which according to our local office study would
translate to an afternoon high temperature at the Tucson
International Airport (KTUS) of 111 degrees Monday. The latest
NBM probabilities (0628/14Z) indicate a 5% chance KTUS will meet
or exceed 110 degrees Sunday, soaring to 55% Monday then back down
to 3% Tuesday. We currently have an Extreme Heat Warning in
effect for the majority of Pima, SE Pinal and portions of Graham
county Monday. I am confident in this product Monday, with
conditions getting close Sunday afternoon as well, maybe not as
widespread.

In any event, we always have a period of several days early-on in
the Monsoon season when we know that we are going to transition
from widespread hot and dry conditions across the forecast area
into a more typical/active thunderstorm regime. That is where we
are. Every year is different. Sometimes you can get a strong surge
of moisture into the region, other years it is a slow creep of
moisture inching northward with daily outflows originating from
Sonora. This year, we get to see a deeper plume of moisture that
has already established itself east of here in New Mexico and
Chihuahua Mexico move in from the east, with a reinforcement of
tropical moisture the second half of the work week into next
weekend.

History has told me that in this type of transition period, we
will see a day before the moisture really moves into the area
where we have severe weather with strong outflows/blowing dust as
the main threat, then potentially a down day as the moisture moves
in, then an active severe/flash-flood threat the following day or
two once the moisture is in place. So, is that first day going to
be Monday late afternoon/evening or Tuesday late afternoon/evening?
I will present the case for both:


Monday could be very interesting with the added ingredient of the
extreme heat anticipated across the entire forecast area. The 500
mb high shifts toward the Four Corners and re-orients itself with
resulting in a potential rim-shot scenario. The leading edge of
the 850-700mb theta-e ridge begins to move into the eastern areas
which would assist convective initiation, then as the storms move
WSW, they will precipitate into a very dry sub-cloud layer
increasing the potential for severe outflow winds/blowing dust.

Tuesday the 500 mb high center starts off similar to Monday, then
begins to lift NE. As this happens, it will result in a more
favorable lifting mechanism due to the stretching deformation
aloft across the eastern portions of our forecast area. The mid-
levels will see a stronger advection of mid-level moisture into
the area with the stronger flow more favorable for organizing
storms. The sub-cloud lower levels will be still very dry for
evaporating downdrafts/severe outflow potential. The heat is still
around but a few degrees cooler compared to Monday due to the
increase in atmospheric moisture and lowering thicknesses.

At this stage either day is plausible, with my hunch is telling
me Monday...but the more likely day being Tuesday.

After that, we will see much deeper atmospheric moisture push
into the area due to the distant influence of the tropical system
currently off the coast of southern Mexico pushing moisture up the
Gulf of California and through Sonora Mexico. The instability
alone from the combination of the deeper moisture and strong
surface heating will allow for an active several days across
Southeast Arizona, with the main threat transitioning from severe
wind/blowing dust to severe wind/blowing dust and now flash
flooding the second half of the work week into next weekend. The
28/12Z models are now trying to establish the southern periphery
of the upper trough dragging though Arizona Thursday which may
result in that day being the most active day. My confidence in the
timing of this feature swinging through is low, but things will be
more clear as we get into the first part of next week.

In any event, get ready this week as it will most definitely be a
change from the hot and dry into the real Monsoon season that we
all know and appreciate.

&&

.AVIATION...Valid through 29/18Z. Mainly SKC this morning, then
SCT clouds at around 10-13k ft AGL aft 28/19Z mainly along the
Int`l border in Cochise County including KDUG and along the AZ/NM
border. There is a slight chc of isold -SHRA/-TSRA for KDUG from
28/19Z-29/04Z but otherwise dry conditions for other terminals.
Isold gusts up to 30-40 kts near any -SHRA/-TSRA, otherwise sfc
winds NWLY at 8-12 kts this afternoon and less than 10 kts
otherwise. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Warmer temperatures and generally dry conditions
this weekend. Isolated showers and thunderstorms this weekend will
mainly be confined along the Int`l border in Cochise County.
Minimum relative humidities from 10 to 20 percent through Monday,
then increasing to 15 to 30 percent Tuesday and Wednesday and 25
to 50 percent Thursday and Friday. Winds generally light and under
15 mph with isolated gusts up to 45 mph under any thunderstorms.
Moisture will be on the increase next week with typical early
monsoon season threats of gusty winds and lightning with lack of
wetting rains through Tuesday. However, widespread rain chances
due to additional moisture move in by mid to late week with the
threats transitioning towards heavy rain and flash flooding.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...

Extreme Heat Warning from 10 AM to 8 PM MST Monday for AZZ501-
502-504>506-509.

&&

$$

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