837
FXUS65 KTWC 282100
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
200 PM 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 today 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. The 500 mb high center is centered over southern
California and western Arizona with a general broad ridge
extending across Southeast Arizona at 300 mb. This broad ridge
will 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
(28/17Z) indicate a 53% Monday then back down to 4% Tuesday of
meeting or exceeding 110 degrees at KTUS. We currently have an
Extreme Heat Warning in effect for the majority of Pima, SE Pinal
and portions of Graham county Monday.

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 due to strong thunderstorm outflows
and blowing dust as the main threats, then potentially a down day
as the moisture moves in, then an active severe/heavy rain/flash-
flooding threat the following day or two once the moisture is in
place. A case can be made that this first day is going to be
Monday late afternoon/evening or Tuesday late afternoon/evening.

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.
These storms will likely lose their steam from central AZ west
because the upper ridge at 300 mb would shut things down.

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 and the stronger flow would be 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 it will occur Monday...but the more likely day for it to occur
is 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 trying to swing the southern periphery of that
upper trough though Arizona Thursday which would make that day
the most active day. My confidence in the timing of this feature
swinging through is low, but things will become more clear in the
next 24-48 hours.

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

&&

.AVIATION...Valid through 30/00Z. SKC-SCT clouds at around 10-13k
ft AGL mainly along the International Border including KDUG and
along the AZ/NM border. Skies becoming SKC overnight, with SKC-
SCT clouds AOA 10-13k ft AGL again Sunday aft 29/19Z. There is a
slight chc of isold -SHRA/-TSRA for KDUG thru 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 International 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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