Flash Flooding and Flood in Arizona, August 20, 2022

Area Forecast Discussion
National Weather Service Tucson AZ
228 AM MST Sat Aug 20 2022

.SYNOPSIS...Shower and thunderstorm chances will continue into
next week with a continued uptick in activity today. The main
threats will be strong gusty winds and heavy rainfall especially
today. Otherwise, temperatures will be 5-10 degrees below normal
into early next week.

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.DISCUSSION...Current radar shows scattered showers across
southeast Arizona. Area gauges at washes and rivers have started
to come down from their peaks caused by earlier rainfall. Water
vapor shows a few upper level lows in the region. One is over the
central Sonora Coast, another is over east central Arizona, and
the third is moving into southern Utah. Models slowly drift the
low over Sonora northward, with the low in Arizona moving off
into New Mexico. Mesoanalysis shows fairly strong upper level
divergence over most of southern Arizona, which will aid in
increasing shower activity early this morning. PWAT values are
near record levels with the KTWC 20/00Z sounding recording 1.98".
This anomalous moisture combined with the upper level forcing from
the low will lead to a continued threat of widespread heavy
rainfall and flash flooding today. Runoff from storms will also
likely lead to a flood threat for area rivers and larger washes.

By Sunday the low over Sonora weakens considerably as high
pressure begins to build back into the Southwest. This high pushes
the low over Utah into Colorado and briefly puts Arizona in
northwesterly mid-level flow. Moisture does decrease a little but
will still be above normal. Expect scattered convection with a
more localized flash flooding threat. Soil moisture will be very
high, so it won't take much rain to cause runoff.

Early next week the high slowly migrates back into the Great
Basin. Thunderstorm activity looks to decrease some as the area
loses some of its moisture. But there will still be enough around
for daily afternoon/evening isolated to scattered showers and
thunderstorms.

Temperatures will be well below normal today and continue to be
below normal through Monday. Tuesday onward temperatures will be
normal to just below normal.

&&

.AVIATION...Valid through 21/12Z.
Slow moving low pressure system over the area will continue to bring
scattered to broken cloud clds, with CIGs down to 3k-6k ft possible
at KOLS for a few hours early in the period. ISOLD/SCT SHRA will
continue through the period with a few embedded TSRA possible in the
area from 20/18Z-20/23Z. Stronger showers and storms could reduce
visibilities in heavy downpours, briefly lower CIGS to 3k-6k ft AGL,
and/or produce gusts of 40+ kts even if only in the vicinity of the
terminal. Otherwise, winds following diurnal trends at speeds of
10kts or less can be expected. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Monsoonal thunderstorm activity will remain elevated
through the weekend with rounds of showers and thunderstorms
expected each day. Primary threats include strong winds, lightning,
and flash flooding. Outside of thunderstorm activity, wind trends
will remain light and follow typical diurnal trends.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this evening for AZZ501>515.

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