Heat in Arizona, August 6, 2021

Area Forecast Discussion
National Weather Service Tucson AZ
951 AM MST Fri Aug 6 2021

.SYNOPSIS...As conditions become more favorable for storms, we
will see a slow downward trend in temperatures along with a
gradual increase in rain and storm chances into next week.

&&
.UPDATE... A slightly more active day is in store for today with
storms expected to initiate between noon-2pm over the higher
elevations. The TWC 12z sounding showed an increase in moisture with
a PWAT of 1.63" which is confined primarily to below 500 mb. Drier
mid-levels heighten the damaging wind concern with storm activity
today. RAP is picking up on this with DCAPE values of 1400-1800 J/kg
this afternoon. After 2 PM, hi-res models are picking up a complex
developing over Santa Cruz County in an area with near 4000 J/kg
CAPE values which will push outflows to the north and west which
will fuel further initiation into this evening. This looks to be the
best chance for Tucson to see some storm activity between 4 PM-8 PM.
Flash flood concerns remain with very little steering flow as ridge
remains overhead.

&&
.DISCUSSION...High pressure over the desert southwest this
morning, with a mid level ridge axis across southern Arizona. That
means a weak flow with weak shear and reliance on gulf surge /
direct outflow for moisture reinforcement. Expect storms to form
near the mountains around mid day and initially struggle to push
into valleys. Fortunately, we should see some weakening of the
ridge this afternoon (just a bit of mid level cooling) along with
a low level moisture convergence field setting up near the border
this afternoon hinted at by NAEFS ensembles. Add in HREF ensemble
mean surface based and MU cape ridge axes from central Sonora
into Santa Cruz / southern Pima county and we have a favorable
area for a convective complex south to southwest of Tucson mid to
late afternoon. Storms will then have an easier time of it forming
along organized outflows.

The weak flow will continue through the weekend as the high tries
to slowly reconsolidate east of us. We will keep enough moisture
for a daily chance of storms, but expect limited storm movement
and support for storms straying away from mountains in their
normal life cycles. Formation and movement will depend largely on
outflows.

Next week is looking good for thunderstorm coverage. Ensembles set
up the mid level high east of our area once again, with an active
tropics and an active mid level easterly wave connection through
central and western Mexico. One such impulse is expected to help
enhance storm coverage Monday afternoon and evening as it rotates
up from the south. The tropical activity isn't expected to provide
direct influences but should help keep things busy upstream
through Sinaloa and Sonora along with helping maintain a steady
flow up the gulf.

&&

.AVIATION...Valid through 07/12Z.
SCT-BKN clouds 12-16k ft MSL through the forecast period. Lingering
isolated -SHRA/-TSRA mainly south of KTUS will diminish early this
morning, then renewed development of scattered SHRA/TSRA expected
aft 06/19Z mainly from KTUS south and eastward, continuing through
07/04Z then gradually diminishing overnight. MVFR cigs/vsbys along
with erratic wind gusts will be possible with TSRA. Otherwise, winds
will remain less than 10 knots. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...
A low to mid grade monsoon pattern is expected through the weekend
with the best thunderstorm chances from Tucson south and eastward.
Near normal temperatures today will gradually lower through the
weekend into next week as moisture increases across the area. This
increased moisture may result in more widespread thunderstorm
activity next week. Strong, erratic winds and locally heavy rainfall
will be possible with any stronger storms that develop. 20-foot
winds will generally be less than 15 mph when not influenced by
thunderstorms.

&&

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

Meyer/Lader/Guillet

Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson