Strong thunderstorms developed in the afternoon over the high terrain of central and southern Arizona before spreading to the lower deserts through the evening, with new development driven mostly by strong outflow boundaries. The primary outflow boundary moved southwest with widespread 30-40 mph wind gusts observed across south-central Arizona and a few stronger gusts, including a 59 mph gust in…
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The episode as NWS PSR wrote it up.
Strong thunderstorms developed in the afternoon over the high terrain of central and southern Arizona before spreading to the lower deserts through the evening, with new development driven mostly by strong outflow boundaries. The primary outflow boundary moved southwest with widespread 30-40 mph wind gusts observed across south-central Arizona and a few stronger gusts, including a 59 mph gust in southern Gila county. The winds were strong enough to cause hundreds of power outages in the Phoenix metro area and generate dense blowing dust over the open deserts in Pinal and western Maricopa counties. With above normal moisture levels, storms also produced localized flash flooding mostly in foothill/high terrain areas, including flash flooding enhanced by recent burn scars.
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 Phoenix, AZ wrote its last area forecast discussion before the first event at Jul 3, 1:52 PM MST, 1 hour 28 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 152 PM MST Sat Jul 3 2021 .SYNOPSIS... Chances for showers and thunderstorms will continue through this weekend with decreasing chances by Monday followed by little chance for the middle of next week. Storms will be common over the higher terrain and more isolated on the lower elevations. Gusty winds with localized blowing dust and localized heavy rainfall capable of producing flash flooding will be the main impacts. Although a general drying and warming trend with above normal temperatures is expected next week across most of the region, isolated storm chances are likely to persist over the eastern Arizona high terrain. && .DISCUSSION… Latest signals from observational and model data point to an active evening across south-central Arizona. The atmosphere is exceptionally moist today with PWATs ranging from 1.5 to 2.0 inches, placing it in the 95th percentile of climatology for the day. Latest RAP streamline analysis depicts the inverted trough across southeastern Arizona, situated between two anticyclones, one across western Texas and another across northern Arizona. The resulting mean layer flow is out of the southeast, which will be favorable to maintain the deeper moisture. Surface dewpoints have only dropped a few degrees this afternoon and remain in the lower 60s. Convection has already initiated along the Mogollon Rim, and across portions of southeastern Arizona near a well-defined vort max. Morning KPHX sounding indicated relatively strong easterly flow of 30 kt at 600 mb, which will help to steer activity into south-central Arizona this evening. Consensus from the CAMs including the HRRR suggests an outflow boundary from storms in the higher terrain will also provide the lift necessary to overcome any low-level CIN in the Valley, while also allowing new cells to propagate rapidly into the deserts south and west of Phoenix. Consequently, PoPs were increased to around 50 percent in the Phoenix area, and as high as 70 percent near Casa Grande. HREF ensemble max gusts are around 50 mph in the strongest storms, and this is not entirely surprising given the anomalously rich low-level moisture and subsequent dearth of DCAPE. Nevertheless, strong wind gusts will still be possible in the vicinity of the outflow boundary as it descends into the lower deserts. However, the greater threat will likely be the potential for flash flooding, particularly across the higher terrain of Gila County and within the recent burn scars. Latest guidance suggests rain rates could reach 1-3 in/hr in the strongest cells. && .PREVIOUS DISCUSSION... A shift in the pattern is expected to begin on Sunday with the drier southerly flow across the western deserts to begin expanding eastward late in the day as well as drier northwesterly mid level flow beginning in the afternoon. Abundant boundary layer moisture will still be present over much of the region on Sunday, but the drying aloft will begin to have a noticeable effect on storm activity, especially across the lower deserts. Showers and storms will again be likely across the eastern Arizona high terrain Sunday afternoon, but they will likely have a more difficult time maintaining their westward push into the south-central Arizona deserts. Can't rule out some isolated to scattered storms affecting the Phoenix area Sunday, but chances mostly drop into a 15-20% range. The westerly drying will continue early next week, likely ending storm chances completely across the lower deserts as early as Monday. Afternoon surface dew points are forecast to drop into the 40s across the western deserts on Monday and then across the south-central Arizona deserts on Tuesday. The upper level ridge center is also seen shifting into Nevada while also strengthening, likely leading to H5 heights increasing to 592-595dm across the Desert Southwest. The drying boundary layer and increased heights aloft should push daytime highs to around 110 degrees in the Phoenix area to 110-113 degrees across the western deserts. So far NBM guidance has been keeping temperatures just below excessive heat levels for next week, but if the upper end of guidance proves true then some heat products may be needed. After a few days of likely minimal monsoon storm activity confined to the eastern Arizona high terrain, there are signs of some moisture return and expansion into the lower deserts at some point later next week. However, the flow pattern through next weekend does not look very conducive for deep moisture advection, likely limiting storm chances across the lower deserts. && .AVIATION...Updated at 1944Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty outflow winds from the east to northeast are expected from distant thunderstorms going into this evening. Strong winds are expected as the outflow moves through with gusts potentially exceeding 30 kts for some locations. The best timing for the arrival of this outflow is currently around 00Z-01Z, though can't rule out a slightly later arrival time. Can't rule out some areas of blowing dust with the outflow, especially at KIWA. The latest HREF guidance shows around a 70% chance of outflow winds exceeding 30 kts this evening across the metro. Additional shower and thunderstorm development is expected during this time across the metro area with gusty erratic winds, lightning, and brief reductions in visibility from rainfall being the main impacts. Lingering showers and thunderstorms are expected to exit the metro by midnight. SCT-BKN clouds are expected to mostly remain aoa 10 kft, though could see bases drop closer to 7-8 kft with any showers and thunderstorms. Southeast California/Southwest Arizona including KIPL and KBLH: Radar showed a few vicinity showers near KIPL; expect this activity to diminish over the next hour or two. Winds are expected to remain light, mostly aob 10 kts, through much of the next 24 hours. Winds will generally favor a southeast to southwest component at both sites with embedded periods of variability. Low chances (<15%) for a few vicinity showers and perhaps a thunderstorm are expected primarily at KBLH later tonight after 05Z. SCT-BKN clouds will continue mainly aoa 10 kft through the period. && .FIRE WEATHER... Tuesday through Saturday: Moisture will decrease gradually through the midweek period, which will generally confine the threat of storms to eastern Arizona. A return of deeper moisture looks possible late next week with storm chances potentially increasing and expanding westward across Arizona. Temperatures for the bulk of the period will run a few to several degrees above normal. Min RH values will drop into the 10-15% range over southeast California and southwest Arizona and 15-25% range over south central Arizona with the highest values over the higher terrain north and east of Phoenix. Max RHs will recover into the 30-45% range for most locations. Apart from thunderstorms, wind patterns will follow diurnal patterns. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...Hirsch PREVIOUS DISCUSSION...Kuhlman AVIATION...Smith FIRE WEATHER...Hirsch/Hopper/Kuhlman
The Phoenix radar (KIWA), 52 km away, was scanning. The volume nearest the first event began at 23:44 UTC.
6 flash flood, 3 dust storm, 1 thunderstorm wind. Local standard time, as filed.
A trained spotter on Interstate 8 at mile post 167 reported visibility briefly fell to 1/4 mile in blowing dust from a strong outflow boundary produced by thunderstorms in northern Pima county. No damages or injuries were reported.
The Globe RAWS weather station (QGLA3), south of Globe proper, measured a 59 mph thunderstorm wind gust. Timing was estimated from radar.
Significant amount of flowing water through Icehouse Canyon and Pinal Creek in Sixshooter Canyon, with downstream flow through Globe, was observed due to heavy rain. Runoff was enhanced by the recent Telegraph burn scar. A spotter in the area reported all major creeks and washes were flowing with ash blackened flood waters. The spotter added that Beer Tree Crossing through Sixshooter Canyon was flooded and there was minor street flooding further downstream. No damages or injuries were reported.
Visibility briefly fell to 1/4 mile in blowing dust along Highway 347 between Riggs Road and Interstate 8. Blowing dust was generated by a strong northward-moving outflow boundary from storms in northern Pima county and reinforced by a storm near the town of Maricopa. There were no reports of damages or injuries.
A trained spotter in Wittman reported visibility briefly fell to less than 1/4 mile in blowing dust generated by a strong southwestward-moving outflow boundary with reinforcing thunderstorms. There were no reports of damages or injuries.
An emergency manager reported a 4-5 foot rise in water in the typically dry Russell Gulch with enhanced runoff from the 2021 Telegraph burn scar. The timing of max flow was estimated. Additionally, Russell Road, which runs through Russell Gulch, was reportedly closed at mile marker 4 by a former trained spotter due to flood waters and burned mud. No damages or injuries were reported.
A Twitter video showed an estimated 6 inches of flowing water over Bush Highway and roughly 3 feet of water collected on the side of the highway at about 1 mile north of the Butcher Jones turnoff. No damages or injuries reported.
Upper Campaign Creek rose 1 to 2 feet. Runoff may have been enhanced by the 2019 Woodbury burn scar. Low water crossing along J Bar Road closed due to flowing water and debris. Time estimated from radar and nearby NWS rain gage. No damage or injuries were reported.
Tonto National Forest closed Butcher Jones Beach Road due to significant flash flooding impacts to the recreational beach and day-use area. Time estimated by radar. No damages or injuries were reported.
Arizona Department of Transportation (ADOT) reported via Twitter that the flood prone state route 238 was closed in both directions between mile markers 25 and 38 due to flooding. The Twitter report was roughly 2 hours after the causative heavy rain. Timing was adjusted based on radar. Radar estimated rainfall was around 1.00-1.25 inches. ADOT reported state route 238 reopened at 20:15 on the 4th. No damages or injuries were reported.
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: 973322, 972111, 972113, 973326, 973328, 973262, 973270, 973264, 973275, 973320.