A slow moving upper level weather system produced periods of heavy rain across southeast Arizona July 24 and 25, especially in Pinal and Pima counties. Flash flooding occurred where soils were already saturated from heavy rains of July 22 and 23 and runoff continued to fill the Santa Cruz River downstream.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS TWC wrote it up.
A slow moving upper level weather system produced periods of heavy rain across southeast Arizona July 24 and 25, especially in Pinal and Pima counties. Flash flooding occurred where soils were already saturated from heavy rains of July 22 and 23 and runoff continued to fill the Santa Cruz River downstream. Floodwaters caused considerable road damage and a levee break in Greene Wash also caused significant damage to a section of a canal in Pinal County. Before the weather system exited the area, another round of heavy rain during the afternoon and evening of July 27 caused additional flash flooding in the Tucson Metro and in Santa Cruz County.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Tucson, AZ wrote its last area forecast discussion before the first event at Jul 24, 9:38 PM MST, 52 minutes earlier.
Area Forecast Discussion National Weather Service Tucson AZ 938 PM MST Sat Jul 24 2021 .SYNOPSIS...An approaching weather system will continue an active monsoon pattern through tomorrow. Showers and storms that develop will be capable of producing heavy rainfall which combined with already saturated ground will result in a high flash flood threat. A decrease in storm activity is expected Monday through midweek. Below normal temperatures will continue through early next week. && .DISCUSSION...As a lobe rotates into the base of the upper low, a more expansive area of convection has developed and is currently south and east of Tucson. Not quite strong enough for lightning at the moment but they continue to be efficient rain producers, more so than a glance at radar would suggest. For example from Green Valley west there is a band with 1-1.5 inches of rain in the last hour. This will continue to pivot to the east and north over the next several hours and will need to monitored for flood issues. Then eyes turn to the second large area of convection headed south, just north of Phoenix. This is associated with another lobe rotating around the low and the last few runs of the HRRR suggest this will continue to work south then east across Pima county to about as far east as Tucson Sunday morning. Given the current setup that seems to be a realistic scenario for the next 12-18 hours. I raised pops for eastern areas earlier tonight then western areas late tonight into Sunday morning and also adjusted the QPF grids as well. The grids and updated forecast have already been sent. && .AVIATION...Valid through 26/00Z. 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 TSRA along with 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 Sunday, 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 Thursday night's 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 && .PREV DISCUSSION... /issued 304 PM MST Sat Jul 24 2021/ The low near the AZ/NM border will continue to dominate our weather with elevated chances of showers and thunderstorms into Sunday. With the ground now saturated, water basins will react very quickly with any additional rainfall. Our Flash Flood Watch remains in effect through Sunday evening. The low is starting to fill a bit with the consolidated center likely to lose some cohesion over the next 12 hours. Short range hi res deterministics and ensembles are in pretty good agreement with some elongation of the low as it pushes through Arizona, reaching the southwest corner of the state by late tomorrow afternoon. Threat for areas of showers and thunderstorms will remain high until then, with subsidence behind the low tending to shut things down Sunday evening. The remnants of the inverted trough should make southern California Monday, with our thoroughly-worked-over atmosphere taking a breather to start the week. With precipitable water values falling back below 1.4 inches (probably down to about 1.25 or so), we should have a couple of afternoons with below average storm coverage. Ensemble means are suggesting the high will remain a little further north than usual, so the easterlies will have plenty of room to remain impactful for our area. Ensembles bring another inverted trough into the weather picture the second half of next week, with a solid impulse pushing across north central Mexico. That will set us up for a strong surge by Thursday afternoon or Thursday night, with a subsequent upturn in thunderstorms (which will probably continue a trend that starts as early as Wednesday afternoon). If the high shifts far enough eastward we could draw the remnants of that wave up from the south and into Arizona Friday or Saturday. That would make things interesting. && .TWC WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Sunday evening for AZZ501>515. && Public...Cerniglia/Meyer Aviation...Zell Fire Weather....Zell Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
The Tucson radar (KEMX), 32 km away, was scanning. The volume nearest the first event began at 05:29 UTC.
9 flash flood, 1 flood. Local standard time, as filed.
Heavy rain of 1 to 1.5 in less than 1 hour fell in Green Valley and caused flash flooding and the closure of several roads. Five homes were flooded in the Casa de Abrego neighborhood, some of which had just been flooded less than 48 hours earlier.
Early morning rainfall of 1 to 1.5 on saturated ground quickly resulted in flash flooding and closure of several roads in north Marana.
Early morning rain of 1 to 1.5 on saturated ground caused flash flooding, closure and damage of Camino Adelante Rd between the Picacho Peak Interstate 10 interchange to Park Link Dr.
More than 1 of rain fell on saturated ground causing flash flooding of several roadways from Sahuarita to Corona De Tucson, including Sahuarita Rd. near Wilmot Rd.
One to two inches of rain on saturated ground cause numerous flooded and closed roads in the Vail area from just east of Rita Ranch to Old Spanish Trail and south to near Interstate 10. One vehicle was stuck in floodwaters near Old Spanish Trail and Drexel Rd.
Widespread rain occurred on July 24 and 25 in the Santa Cruz River watershed in Pinal County and upstream in much of eastern Pima County with 48 hour rain totals of 3 to 4 inches common. High flows in the river traveled downstream into Greene Wash. A levee breached in the wash near Toltec Buttes and washed out a road, then flowed into a canal, causing damage along 3/4 mile of the canal. Further downstream in Greene Wash, Sunland Gin Rd was also flooded and damaged. Indian Route 15 near Chuichu was also flooded and two nearby homes sustained minor flood damage.
Up to 1 of rain on saturated ground caused Franco Wash to rise rapidly and flood and damage several roads in the Summit area.
One to two inches of rain fell in less than 1 hour in Nogales and caused flash flooding of several roads and minor damage to a couple of homes near Western Ave.
Around 2.5 of rain in less than 1 hour was measured near the headwaters of Sabino Creek in the Bighorn burn scar and caused a two-foot rise in the stream that crosses trails in the Sabino Canyon Recreation Area. Six hikers had to be rescued after becoming trapped by the high flows.
Heavy rain of 2.5 in less than 90 minutes occurred near the headwaters of Rincon Creek. Flash flooding occurred downstream in the Rincon Ranch Estates area. Camino Loma Alta became flooded and impassible.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2021Every state in 2021This day in weather historyWarnings in Arizona, July 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 976377, 976392, 976399, 976414, 976418, 976446, 976441, 976518, 976524, 976529.