Flash Flooding and Dust Storm in Arizona, August 13 to 14, 2021

Mesonet station MAHL at Horseshoe Lake measured a 63 mph wind gust.

Numerous tree branches of varying sizes blown down. Wind gusts estimated 50 to 60 mph. No injuries reported.

Visibility fell to less than one quarter mile in blowing dust near Duane Lane and 227th Avenue. No damages or injuries were reported.

A home weather station measured a 60 mph wind gust.

A photo on social media shows a metal patio awning blew down in strong winds near 19th Avenue and Bell Road. Winds estimated around 50 to 55 mph and timing based on radar. No injuries were reported.

Photo on social media shows two unoccupied sedans floating in flood water near Helena Drive and 2nd Street. Flood water continued down the water channel and spilled into the apartment complex on Bell Road and Central Avenue. Broadcast media reported multiple ground floor apartments experienced flood damage with an estimated 4 feet of water moving through them. Extent of the damages and number of apartments affected was not reported. Time estimated from radar. No injuries were reported.

Multiple large trees were blown over due to strong winds at Latitude Apartment Complex near 19th Avenue and Thunderbird Road. One tree fell on a second story unit, causing unknown damage. Another couple fell on portions of carports that caused the carports to collapse and damage an unknown number of cars that were parked underneath. A separate carport also experienced damage. Winds were estimated up to 55 to 65 mph based on radar and timing was based on radar as well. No injuries were reported.

The Greenway Road underpass at Interstate-17 flooded with a few feet of standing water and was closed as a result. Before being closed, a reported 5 vehicles stalled in the flood water, requiring a rescue. The underpass did not reopen until roughly noon on the 14th. No injuries were reported.

Roof partially torn off in strong winds near Interstate-17 and Thunderbird Road. Winds estimated around 55 to 65 mph. Timing based on radar. No injuries reported.

Public report of flooding along 23rd Avenue between Dunlap Avenue and Northern Avenue. Video shows the intersection of 23rd Avenue and Butler Drive flooded with at least 6 inches of water. No damages or injuries were reported.

Video on social media showed significant flow in Ashbrook Wash over El Pueblo Boulevard just north of Grande Boulevard. In the video an uprooted mature palo verde tree was flowing across the road. The following morning it was found that a sedan had been swept off the road at some point during the night and crushed by debris, but the owner of the vehicle was able to escape. No injuries were reported.

Large shallow-rooted tree uprooted and fell into the street near Miller Road and Southern Avenue. Wind speeds estimated between 45 to 55 mph. Timing estimated from radar. No injuries were reported.

Heavy rain led to a partial roof collapse of the Moon Valley Bible Church. The roof collapsed in the storage area and broke the main water pipe which flooded the entire roughly 30,000 square foot building with an estimated 4 inches of water. Rainfall amounts around 1.5 to 2.0 inches were measured in roughly an hour or less by many gages in the area. The church was hit by another storm a few days later that flooded the building again. No one was in the building at the time of the collapse and there were no injuries. Damage costs were estimated to be around $1 million.

Interstate-17 was closed in both directions due to significant standing water on the freeway near Indian School Road. Multiple cars also became stalled in the standing water. Interstate-17 was not fully reopened until approximately 0115MST on the 14th. No injuries were reported.

Multiple streamflow gages along Indian Bend Wash exceeded action or alarm stage, particularly between Highway-51 and Scottsdale Road. Streamflow gages crested around 3 to 5 feet and most did not fall below action or alarm until midday on the 14th. The USGS gage at Sweetwater Avenue recorded a roughly 4 foot rise in 30 minutes and crested at 3.95 feet. Rainfall amounts between 1.5 to 2.5 inches were measured upstream just west of Highway-51. No damages or injuries were reported.

Arizona Department of Transportation reported State Route 88 was closed in both directions between mile posts 229 and 242 due to flooding. Timing estimated based on radar. No damages or injuries were reported.

Public report, confirmed by police, that a road was blocked by downed power lines at 83rd Avenue and Broadway Road. Winds estimated around 55-65 mph and timing estimated from radar. No injuries reported.

The SRP32 mesonet station near 43rd Avenue and Lower Buckeye Road measured a 61 mph wind gust. A microburst signature was observed on radar in this area. The Phoenix terminal doppler weather radar TPHX, near 51st Avenue and Lower Buckeye Road, took a direct hit and stopped transmitting after its 1039MST scan. There were no damages to TPHX reported and it was restored by 1000MST on the 14th.

A 40 foot tree fell through a 5 foot cinderblock wall and onto a chicken coop at a home near University Drive and 96th Street. There were no chickens in the coop at the time and no injuries were reported. Winds were estimated around 55 to 65 mph. Timing estimated from radar.

Photos from APS utility company on social media show several downed or snapped wooden and metal power poles along 27th Avenue just north of Durango Street. A microburst signature was evident on radar in this area. Winds were estimated around 60-65 mph based on a 61 mph measured gust a few blocks away. No injuries were reported.

A strong downburst knocked over or broke 20 to 30 trees and a few saguaro cacti along Brown Road and Ellsworth Road. Winds estimated around 55-65 mph and timing based on radar. No injuries reported.

Video shows a large tree snapped near the base and fell on a home near University Drive and Lindsey Road causing damage. The extent of the damage was not reported. Winds were estimated around 50 to 60 mph based on radar. Timing estimated from radar. No injuries were reported.

Interstate-17 was closed in both directions at the Durango Street curve due to standing water on the freeway, making it impassable. Interstate-17 did not fully reopen until approximately 0100MST on the 14th. No damages or injuries were reported.

Thunderbird Road from Interstate-17 to 35th Avenue flooded with 1 to 3 feet of standing water. At least one car became stranded in the underpass below Interstate-17. The underpass was closed for several hours. No injuries were reported.

A tattoo shop at a strip mall near University and Recker flooded with 16 inches of water after the roof of the adjacent vacant shop fully collapsed. The tattoo shop owners estimated the cost of their damaged or destroyed interior belongings at $17,000. There were no injuries. Timing based on heaviest rainfall in the area. A few rain gages in the area measured around 1.5 to 2.5 inches in roughly 1 hour.

City of Surprise closed Cotton Lane between Peoria Avenue to Cactus Road due to flooding. No damages or injuries were reported.

The City of Surprise closed Jomax Road between 147th Avenue and El Granada Road due to flooding. No damages or injuries were reported. Timing based on radar.

Video on social media shows at least 6 inches of swift-moving water flowing down 96th Street near Duncan Street. No damages of injuries were reported.

Five metal transmission towers were knocked over in severe straight line winds. Winds were estimated around 70 to 80 mph based on the damage. Timing estimated from radar. No injuries were reported.

Arizona Department of Transportation reported that US-60 was closed in both directions between Superior and Top-Of-The-World, specifically between mileposts 227 and 235, due to rocks on the roadway following heavy rainfall in the area. The highway was reopened around 0030MST on the 14th. No damages or injuries were reported.

Photos on social media showed considerable tree debris washed up against a walking bridge along with washed out trails and picnic area at the Boyce Thompson Arboretum due to high flow in Queen Creek and/or Silver King Wash. As a result of the damage left behind from the flooding, the picnic area along with a couple of gardens and trails were closed. Further downstream, a USGS stream gage along Queen Creek below Whitlow Dam recorded a rapid rise near midnight going from the 13th into the 14th. Discontinuities in the data suggest that the flow in Queen Creek exceeded the gage's 6 ft maximum operating limit at around 0230MST when the gage recorded a height of 5.37 ft. Timing was estimated using the USGS gage. No injuries were reported.

Report through mPing of impassable street flooding in the town of Maricopa. Additional details not reported.

Highway 72 was flooded and impassable near Bouse. Timing adjusted based on radar. No damages or injuries were reported.

Arizona Department of Transportation reported via social media at 0202MST on the 14th that Highway-238 was closed in both directions between milepost 40 near Maricopa and State Route 85 near Gila Bend due to flooding. Heaviest rain, estimated around 2 to 3 inches, fell from the Maricopa mountains west toward Gila Bend. Highway-238 would remain closed through the 14th. Timing of impacts adjusted based on radar. No damages or injuries were reported.

Maricopa County Department of Transportation reported at 0226MST that Agua Caliente Road, a dirt road, was closed between Old US 80 to Lahman Road due to flooding. Timing of impacts adjusted based on radar and location focused on area with greatest radar rainfall estimates. No damages or injuries were reported.

Following 2 to 4 inches of rain in 1 to 2 hours over the Sand Tank Wash watershed, catastrophic flooding occurred in the small town of Gila Bend with feet of water, mud, and debris moving through town. Storm surveys were completed by NWS Phoenix, Maricopa County Department of Emergency Management (MCDEM), American Red Cross, and Flood Control District of Maricopa County (FCDMC). FCDMC gages on Sand Tank Wash, Bender Wash, and in the Maricopa Mountains measured rainfall amounts around 3 to 4 inches in 1 to 2 hours for an annual exceedance probability of 0.1%. FCDMC found the most significant floodwaters were within Sand Tank Wash, with lesser flows in Bender and Scott Avenue Washes. The NWS Phoenix survey found evidence of out of bank flooding in Sand Tank Wash 1 to 3 miles south of Interstate-8 (I-8) with 2 to 6 feet of water and sizable debris. The streamflow gage on Sand Tank Wash at I-8 reached alarm stage at 0157MST, bank full at 0341MST, and flood stage at 0352MST. The gage crested at 7.69 feet with 5000 cfs of flow at 0408MST. The floodwaters and debris that moved through town caused flood damage to at least 140 homes and 25 businesses. Most structures impacted were between the Gila Bend Canal and Main Street and then along Pima Street. During the flooding, Maricopa County Sheriff's Office rescued at least 30 individuals from their roofs along with others pulled from stranded vehicles. Photos after the water receded showed the canal was eroded and breached where Sand Tank Wash flows over it. Photos also showed 2 to 5 foot water lines both on the outside and inside of many of the structures, piles of debris, damaged property and vehicles, and erosion. Of the homes MCDEM assessed, 21 were deemed uninhabitable after the flooding. Unfortunately there were 2 direct fatalities with this event. One made a heroic effort to save a stranded motorist before they themselves were swept away in their own vehicle. The other was swept away in one of the flooded washes. Additionally, many farm animals were killed. Besides the fatalities, no other injuries were reported. A state of emergency was declared for this event.

Visibility fell to less than one quarter mile in blowing dust near Avenue 42 E and County 7th Street S in Tacna. No damages or injuries were reported.

A streamflow gage on the Agua Fria River at Buckeye Road exceeded alarm stage at 0241MST with peak flow of 1932 cfs and a crest height of 0.79 feet. Impacts to the low water crossing at Lower Buckeye Road are common with this flow level, but no impacts were reported. No damages or injuries were reported.

A streamflow gage on Sauceda wash near Highway 85 exceeded alarm stage at 0349MST, with a peak flow of 1396 cfs and crest of 4.10 feet at 0509MST. The stage fell below alarm at 0552MST. With alarm stage flow, impacts to Watermelon Road just north of Interstate-8 can experience impacts, but none were reported. No damages or injuries were reported with this flow, but catastrophic impacts, including loss of life, were experienced in nearby Gila Bend from flooding of Sand Tank wash. See that event entry for details.