July 21st: Severe Storms In Mesa

A very unstable and moist atmosphere was over much of the state/valley on July 21st, with any synoptic trigger likely to allow thunderstorms to develop. One such trigger mechanism moved into east Mesa during the late afternoon/early evening, in the form of two converging outflows. One outflow was moving in from the east, which was produced by thunderstorms earlier in the afternoon to the east and southeast. A second, and stronger outflow was produced by a thunderstorm which developed over the San Tan Mountains, to the south.

Around 7:13pm, these two outflows were beginning to converge over Apache Junction and east Mesa. Just ahead of this convergence zone, two thunderstorms began to develop across portions of east Mesa. By 7:31pm, Doppler Radar indicated that these two storms merged into one strong to severe thunderstorm (from about Val Vista to Signal Butte and US 60 to just north of Thomas). With these storms nearly stationary, a large amount of rain occurred in the affected location. Doppler Radar estimated rain totals were in the 2.00 to 2.75in. range. The loop above/right is the Base Reflectivity (1.4°) Doppler Radar imagery from 7:13pm to 7:31pm, showing the two outflows, as well as, the two storms forming and then merging into one strong/severe thunderstorm.

These strong to severe thunderstorms continued to affect east Mesa until around 8:18pm, where soon after they quickly dissipated and were nearly none existent by 8:30pm. From the time the storms began around 7:13pm to when they disappointed, several strong downburst (possible microbursts) occurred across Mesa, however the National Weather Service has not yet officially stated whether microburst actually occurred. Below are some of the strong microbursts that may have occurred (in order of occurrence), which knocked down power lines and numerous trees, with homes even being severely damaged around University and 62nd Street.

The first downburst likely occurred between 7:13pm and 7:22pm, between McKellips Road to University Road and Signal Butte to Hawes Road. The image below is a cross section from 7:17pm, showing the start of this possible downburst. Click the links below to view loops of different radar products of this event from 7:08pm to 7:26pm.

Product: Reflectivity Cross Section
Information: Cross section is 24,425ft in height and each horizontal section is roughly 8,100ft. Length is 4.91nm.
[Click Here To View]

Product: Base Reflectivity 1.0° scans
Information: White line indicates the line creating the cross section.
[Click Here To View]

Product: Base Velocity 0.6° scans
[Click Here To View]


The second outflow, which was likely much stronger than the first occurred sometime between 7:26pm and 7:31pm, within the area of Main Street to Brown Road and Recker to Power Road. This potential location corresponds well with the house that had severe roof damage around 62nd Street and University, along with the 60mph wind gust reported at McKellips and Power Road at 7:41pm. The image below shows the cross section of this strong downburst, taken at 7:31pm. Click the links below to view loops of different radar products of this event from 7:17pm to 7:45pm.

Product: Reflectivity Cross Section
Information: Cross section is 21,284ft in height and each horizontal section is roughly 10,500ft. Length is 4.27nm.
[Click Here To View]

Product: Base Reflectivity 1.0° scans
Information: White line indicates the line creating the cross section.
[Click Here To View]

Product: Base Velocity 0.6° scans
[Click Here To View]

The third, and final possible downburst/microburst we will examine likely occurred between 7:45pm to 7:54pm, in the area contained by Main Street to US 60 and Higley Road to Power Road. This corresponds well with numerous trees being knocked down in the Bashas' parking lot near Broadway and Power, along with the power lines that were reported down along Southern just east of Power at 7:55pm. The event can also be seen quite clearly in the photos that Peter sent us from Gold Canyon, taken near Peralta Trail Elementary School, looking toward Mesa. Click HERE for the photo taken at 7:47pm and click HERE for the photo taken at 7:50pm. The cross section below was taken at 7:49pm. Click the links below to view loops of different radar products of this event from 7:31pm to 8:08pm
Product: Reflectivity Cross Section
Information: Cross section is 18,567ft in height and each horizontal section is roughly 9,300ft. Length is 4.04nm.
[Click Here To View]

Product: Base Reflectivity 1.0° scans
Information: White line indicates the line creating the cross section.
[Click Here To View]

Product: Base Velocity 0.6° scans
[Click Here To View]

Overall, this was a very fast forming and fairly localized, severe thunderstorm that affected east Mesa, causing extensive damage in some locations. If you have any questions or comments about anything above, feel free to contact us. Also, if you have any photos of this storm you would like to share, please click HERE for details .