Heat in Arizona, July 6, 2021

Area Forecast Discussion
National Weather Service Tucson AZ
854 AM MST Tue Jul 6 2021

.SYNOPSIS...A drying trend will curtail thunderstorm coverage the
rest of the week. As this happens, temperatures will climb
several degrees. Conditions look favorable for an increase in
thunderstorm chances by early next week.

&&

.DISCUSSION...Satellite imagery depicts remnant debris clouds that
are in the process of dissipating. Radar is scanning isolated light
showers along the International Border near Sasabe moving toward the
southwest. The morning sounding measured 1.78" PW, which is yet
morning near record levels. The monsoon ridge is currently centered
near the NV/UT border, producing northeasterly steering flow across
our region.

Thunderstorm activity is trending down for some portions of the
forecast area, but model guidance is in fairly good agreement
keeping development east of Tucson over Graham/Greenlee/Cochise
Counties perhaps sneaking into Santa Cruz as well. This is in
concert with the best instability, which models show SB CAPE around
500-1000 J/kg in the late morning/afternoon. Storms will drift
toward the south or southwest and with the abundant moisture still
available, flash flooding and wet microburst remain the primary
threat. DCAPE will be best over Graham/Greenlee, which may produce a
nice organized outflow coming off the high terrain into the Gila
River Valley. For details on the days to come, please see the
previous discussion below.

&&

.AVIATION...Valid through 07/18Z.
SCT-BKN clouds 8k-12k ft MSL through the period with layers above at
times. The greater cloud coverage will be east and south of Tucson.
Isolated SHRA/TSRA will be possible mainly along the international
border and the AZ/NM border. There is low probability that KTUS will
be impacted by storms. Wind gusts to 40 kts possible near TSRA.
Otherwise sfc winds will be SE this morning becoming NW this
afternoon and evening with speeds 5-10 kts. Aviation discussion not
updated for TAF amendments.

&&

.FIRE WEATHER...Expect slightly reduced storm coverage this week
with isolated to scattered showers and thunderstorms mainly from
central Pima County eastward. Best chances each day will be along
the international border and and AZ/NM border. Min RH values will
generally be in the 20-35 percent range for lower elevations through
the weekend with very good overnight recoveries. Today looks to be
the driest day with RH values in the upper teens from Tucson
northwestward. General winds will be light through the week and
following normal daily trends when not influenced by storms. The
only exception is the Gila River Valley which will see elevated
winds today and this weekend.

&&

.Prev Discussion...A few showers out there this morning; leftovers
drifting in from the northeast. Today transitions the high center
across Arizona and into southern Nevada/Utah. Some mid level warming
and weak subsidence along with the gradual drying trend should mean
another reduction in thunderstorm coverage today. Favored areas
again east and south of Tucson. Wet microbursts still supported by
this level of moisture, and additional insolation could make them
friskier where they have outflow support for additional lift. Keep
an eye on an organized outflow off the rim with a steeper
orientation than usual. Instead of a push toward Phoenix and Tucson,
it would tend to head due south through Graham and into Cochise
county. Elsewhere, without that additional lift storms should
struggle in lower elevations.

Other than a brief wobble to the east Thursday, our high center is
going to stay in a less favorable position for reinforcing the
moisture still currently in place. We won't shut down, but coverage
will be limited compared to the Holiday weekend.

A couple of interesting things to watch. First, ensembles are still
advertising a strong easterly wave across central and northern
Mexico Friday and Saturday. That would support a deep moisture surge
back into southern Arizona over the weekend. Add in a potential
inverted trough around the eastern periphery of the high position,
and we could really be cooking again early next week. Fingers
crossed for a solid trend upward as early as Friday or Saturday.
Friday because of a weaker but not insignificant surge into
southcentral and southwest deserts Thursday (as per both NAEFS and
ECMWF mean integrated water vapor transport trends).

&&

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

&&

Discussion...Howlett
Previous Discussion...Meyer/Hardin

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