Areal Flood Advisory 79, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
213 AM MST Sun Jul 25 2021

.SYNOPSIS...
The final day of this active weather period is upon us as a
weather system passes through the area today. Rounds of showers
and storms capable of producing heavy rainfall and flash flooding
will be present across southeast Arizona through late today. A few
slower days are expected from Monday through mid-week with
temperatures warming back up to near normal.

&&

.DISCUSSION...
Today and tonight. The low pressure system that we have been
discussing for the past few days finally pushed into east Arizona
late tonight. There are two main areas of precipitation currently
associated with this low including one moving to the northeast
over southeast AZ on the south side of the low and the second
pushing southwestward across the Phoenix area on the western edge
of the low. The first area is bringing rain rates of up to 0.20
inches an hour to most areas but there are a few pockets that are
receiving between 0.20-0.50 inches an hour which have been mostly
minor in terms of impacts. This second area, associated with an
MCV moving across Phoenix, will expand across central Pima County
and southwest Pinal County approaching sunrise in an unstable
environment with CAPE values of 1000-1500 J/kg. This area will be
the focus for activity throughout the morning. By the afternoon,
the best chances will shift to areas that didn't see a lot of
action this morning which would be across Cochise, Greenlee,
Graham, and western Pima counties in particular. Flash flooding
remains the primary threat today. As the low moves overhead,
steering flow will become very weak which combined with saturated
ground and PWAT values of 1.2-2.1 inches from east to west
respectively, the threat of flash flooding remains high. Flash
Flood Watch remains intact through tonight.

The low will exit to the west late Sunday into early Monday with
some drying occuring on the backside as PWAT values drop to
1.0-1.6 inches. Ridge will build back in, centering off to the
northeast of the Four Corners region through late this week. A
decrease in overall convection will be the result Monday through
Wednesday with isolated to scattered, diurnally-drive storms
expected. Temps will begin a warming trend, reaching near normal
values by midweek. The latter half of the week could see
increasing storm activity as an easterly wave treks across TX and
northern Mexico, shifting northwestward towards southern Arizona
Thursday into Friday. This feature has been picked up on the last
several ensemble runs with slight variability in the strength as
it moves towards the local area.

&&

.AVIATION...Valid through 26/12Z.
SCT-BKN clouds at 7k-11k ft MSL thru the period, along with periods
of SHRA/TSRA. Expect MVFR CIGS/VSBYS and mountain obscurations
around SHRA/TSRA particularly during the morning hours. TSRA will
also be capable of producing gusty outflow winds, potentially in
excess of 40 kts with the strongest storms. Otherwise, SFC wind
generally less than 12 kts. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Periods of heavy rainfall are expected through
today, with scattered to numerous showers and thunderstorms.
Flooding issues are expected to continue, due to part to saturated
soils. Showers and storms will be possible through the day and also
at night. Gusty winds in excess of 40 mph and numerous lightning
strikes may accompany stronger storms. Daytime temperatures will
remain below normal. 20-foot winds will generally be less than 15
mph when not influenced by thunderstorms. Shower and thunderstorm
chances decrease slightly Monday through the middle of next week.

&&

.HYDROLOGY...Given the chance for heavy rainfall and already
saturated soils the potential for flows in rivers and washes is
high.

A couple of potential trouble areas to make note of...Finger Rock
and Sabino Canyon. Significant sediment and silt have moved around
the Finger Rock area with recent activity, causing some localized
damage. Any additional high rainfall rates in this area could
cause more trouble. Sabino Canyon also is an area to keep an eye
on, where high rainfall rates could cause issues quickly.

Most river forecasts across southeast Arizona show elevated stream
flow over the weekend. With high enough rainfall amounts other
locations could reach flood stage and possibly out of bank flow.
Stream flow may also take longer to recede if basin receives multiple
days of rainfall. Potentially leading to elevated stream flow into
early next week.

River observations and forecasts can be found at the following
sites:
https://water.weather.gov/ahps2/index.php?wfo=twc
http://www.cbrfc.noaa.gov

&&

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

&&

Public...Guillet
Aviation...Carpenter
Fire Weather....Carpenter

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