599
FXUS65 KTWC 280800
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
100 AM MST Tue Jul 28 2026

.SYNOPSIS...Expect daily afternoon and evening showers and
thunderstorms this week with day to day variability in coverage
and strength. High temperatures will be 2-6 degrees above normal
today and Wednesday then warm to 7-12 degrees above normal
Thursday into the weekend.

&&

.DISCUSSION...A large MCS is slowly moving northwestward through
Sonora and Santa Cruz County/southern Pima County and scattered
convection is moving through Graham County. An outflow recently
passed through Tucson with gusts 30-40 mph out of the south. IR
satellite shows the MCS cloud tops warming, but locally heavy
rainfall and gusts to 45 mph will be a threat through the night
and early morning. This overnight activity is being helped by
an easterly wave that is currently over north central Sonora as
well as 0-6 km shear of 25-35 kts and ample moisture. The
easterly wave will move northward this morning into the
afternoon through western Pima County and into western Arizona.
Isolated showers and thunderstorms will likely continue through
the morning south and west of Tucson. Hi-res guidance shows the
convection over Graham County dissipating over the next few
hours.

Left over debris clouds from the MCS will likely inhibit
convection from Tucson west this afternoon and evening. HREF and
REFS members show isolated to scattered convection east of
Tucson with the best chances along the AZ/NM border. The center
of the upper level high will be over northern New Mexico with
mid-level flow elevated at 15-20 kts. The environment east of
Tucson will be similar to Monday with PWAT values ranging from
1.2"-1.7", CAPE around 1000 J/kg where there is sufficient
insolation to erode any capping, and 0-6 km wind shear of 25-35
kts. Because of this any storms do form may have rotating
updrafts and be capable severe wind gusts along with heavy
rainfall. The main uncertainty today will be the extent of storm
coverage in the wake of the MCS. Right now the AZ/NM border
looks to have the best chances for convection.

Wednesday mid-level winds decrease 5-10 kts which also leads to
a reduction in wind shear with 0-6 km shear generally around 20
kts from Tucson eastward. All other ingredients will be in place
however with similar PWAT values to today and plenty of
instability once surface heating starts. Hi-res guidance again
favors convection south and east of Tucson with the
international border and White Mountains seeing the best
chances. Tucson will likely be on the northern periphery of
storm chances, but can`t rule out an isolated thunderstorm or
two over town.

After Wednesday the ridge expands westward and strengthens with
NAEFS mean 500 mb heights at the 99.5 percentile or max compared
to the CFSR climatology Thursday into the weekend. Temperatures
warm 7-12 degrees above normal during this time frame leading
to widespread areas of Major to Extreme HeatRisk. Because of
this an Extreme Heat Warning is in place Thursday through
Sunday. The two warmest days look to be Friday and Saturday with
Tucson possibly seeing 110 degrees both days. NBM probabilities
for Tucson International to hit 110 degrees are 60-70 percent
both days. Storm chances and coverage will likely be limited to
mainly the White Mountains Thursday thanks to the placement of
the ridge and loss of moisture. PWAT values decrease by about
0.25" and surface dewpoints decrease to 50-55 degrees. Friday
into the weekend moisture returns leading to storm chances
slowly increasing and expanding to central Pima County eastward
by Sunday into early next week.

&&

.AVIATION...Valid though 29/12Z.
Isolated to scattered TSRA possible from central Pima County
eastward through 28/15Z with cigs 6k-10k ft AGL. KDUG and KOLS
terminals will be most at risk of being impacted by TSRA. Then
expect a brief break in convection before storm chances increase
again mainly along the AZ/NM border this afternoon and evening.
KDUG and KSAD terminals will see the best chances to be
impacted by TSRA this afternoon and evening. Cigs will be
8k-12k ft AGL this afternoon and evening. Any thunderstorm may
produce wind gusts in excess of 40 kts. Outside of storms
surface winds variable less than 8 kts this morning becoming
NWLY 6-10 kts with occasional gusts this afternoon and evening.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...High temperatures will remain above normal this
week with an Extreme Heat Warning in place Thursday through
Saturday. Expect daily chances of afternoon and evening showers
and thunderstorms with day-to- day variability on coverage of
storms into the weekend. Any thunderstorm will bring a threat
of severe, erratic wind gusts as well as brief heavy rainfall
and an isolated threat of flash flooding. Minimum relative
humidity values will be 20-40 percent in the lower deserts
through at least mid-week. Winds this weekend will mainly be
light and under 12 mph outside of thunderstorms.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 5 AM MST early this morning for AZZ503-507-
513-515.
Extreme Heat Warning from 10 AM Thursday to 8 PM MST Sunday
for AZZ501>509.

&&

$$

Hardin

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