Weather balloon data from the evening of the 28th. Note the large amount of instability with the weak cap. Also note the deep northeasterly flow in the mid levels.
During the day of the 28th, the sky was mostly clear across central Arizona. Early indications were that strong to severe thunderstorms were possible that evening, though by mid-afternoon little thunderstorm activity had developed. The weather balloon sounding data from Phoenix Thursday evening indicated that the atmosphere remained very unstable though a cap remained - analogous to a lid on a pot of boiling water (see graphic to right). In addition winds in the mid levels of the atmosphere were over 45 mph from the northeast, strongly unusual and indicative that thunderstorms that develop northeast of Phoenix will quickly move into the lower deserts and be capable of producing damaging winds.
Infrared satellite imagery. Click on the image for a larger version.
Shortly after 8 PM, thunderstorms began to develop east of Phoenix and moved into the potentially very unstable airmass. The thunderstorms themselves provided enough lift to release the stored energy - they took the lid off the pot. In the ensuing four hours severe thunderstorms spread across much of the south central Arizona, including much of the Phoenix Metropolitan Area. These were not your typical monsoon thunderstorms. NWS meteorologists noted the exceptionally strong structure of the thunderstorms, with the storms themselves extending up to 60,000 feet in the atmosphere. At this height the temperature of the tops of the thunderstorms was below -110 deg F (see graphic to right). For a satellite image loop, click here (0.8 MB).
80 to 100 mph winds measured by radar. Click on the image above for a full size version with accompanying text.
As the evening unfolded several waves of thunderstorms, about four in total, developed generally east or northeast of Phoenix and moved to the west or southwest at speeds ranging from 20 to 40 mph. For a radar loop of the full event click here (large file - 17 MB). Early on it became evident that these thunderstorms would be capable of producing severe and damaging winds. This is what in fact happened as significant bow echoes developed within each wave. The highest measured wind speed reported to the NWS was 85 MPH, which occurred near central Phoenix. Phoenix Sky Harbor International Airport reached 75 mph. Even the NWS office in Tempe was hit by the damaging winds. NWS meteorologists estimating winds to be at or above 80 MPH at the NWS office. Winds may have actually been higher than reported by any ground-based weather station as the National Weather Service radar recorded winds in excess of 100 MPH just 1,500 feet above the ground (see to right). For a loop of velocity radar data click here (large file - 14 MB).
The National Weather Service in Phoenix issued twenty Severe Thunderstorm Warnings and received thirty reports of severe weather during the event. The most significant wind measured was a wind gust of 85 MPH 4 miles SSE of downtown Phoenix by a trained weather spotter. The very strong winds resulted in widespread damage, with central Phoenix and north Tempe taking the brunt of the storm. Media coverage indicated that downed trees occurred over a large area with perhaps thousands of trees lost during the storm. Structural damage was also observed. The images below were taken by NWS Employees. Click on each thumbnail for a full version image.
Another interesting angle which indicates just how strong these thunderstorms were is the fact that a record low for the date was tied at Phoenix Sky Harbor International Airport. During the height of the thunderstorms the temperature dropped to 64 degrees. This tied the record low for the date, previously set in 1920. The setting or tying of a record low temperature at Sky Harbor has become a rare event during the past two decades. Record high lows have become much more prevalent primarily dur to the expansion and intensification of the urban heat island. In fact this was the first record low that has been set or tied since 23 December 1990 - nearly twenty years. It was also the first record low set or tied during the summer since 1979 and during August since 1968 (forty years!). These numbers indicate just how strong the thunderstorms were that impacted the Phoenix area.
The ASU football practice field was destroyed by the winds.
It is likely that thousands of trees like these fell during the storm.
It is likely that thousands of trees like these fell during the storm.
This covered parking was no match for the strong winds.
More structural damage.
PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE PHOENIX AZ
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0825 PM TSTM WND GST 2 S CHANDLER 33.27N 111.87W
08/28/2008 M77.00 MPH MARICOPA AZ AWOS
CHANDLER AIRPORT
0830 PM HEAVY RAIN 5 S CHANDLER 33.22N 111.88W
08/28/2008 M0.22 INCH MARICOPA AZ AMATEUR RADIO
0.22 INCH IN 5 MINS
0830 PM HEAVY RAIN 3 ENE CHANDLER 33.31N 111.82W
08/28/2008 M0.50 INCH MARICOPA AZ TRAINED SPOTTER
0.5 INCH RAIN IN 10 MINS
0840 PM HEAVY RAIN 5 W CHANDLER 33.29N 111.95W
08/28/2008 E0.50 INCH MARICOPA AZ TRAINED SPOTTER
0.5 INCH IN 30 MINS.
0850 PM HAIL 7 SW GUADALUPE 33.30N 112.06W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
3/4 INCH HAIL REPT LIBERTY LN AND DESERT FOOTHILLS PKWY
0850 PM HAIL 4 SW GUADALUPE 33.32N 112.00W
08/28/2008 E0.75 INCH MARICOPA AZ NWS EMPLOYEE
0906 PM HAIL NW MARICOPA 33.06N 112.05W
08/28/2008 E0.25 INCH PINAL AZ TRAINED SPOTTER
1/4 INCH HAIL COMPLETELY COVERING GROUND
0910 PM HEAVY RAIN 1 SW KINGS RANCH 33.37N 111.45W
08/28/2008 M0.50 INCH PINAL AZ TRAINED SPOTTER
HALF INCH RAIN IN 9 MINUTES
0912 PM HEAVY RAIN 4 E APACHE JUNCTION 33.40N 111.48W
08/28/2008 M0.00 INCH PINAL AZ TRAINED SPOTTER
0.27 INCH RAIN IN 7 MINUTES
0919 PM HEAVY RAIN 2 NW APACHE JUNCTION 33.42N 111.57W
08/28/2008 E0.00 INCH PINAL AZ TRAINED SPOTTER
1.2 INCH IN 25 MINS
0920 PM TSTM WND GST 3 NE MESA 33.45N 111.70W
08/28/2008 E75.00 MPH MARICOPA AZ TRAINED SPOTTER
RECKER AND BROWN
0920 PM HAIL 3 NE MESA 33.45N 111.70W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
BROWN AND RECKER IN EAST MESA
0921 PM HEAVY RAIN 5 WSW APACHE JUNCTION 33.39N 111.63W
08/28/2008 M0.00 INCH MARICOPA AZ TRAINED SPOTTER
0.5 INCH IN 15 MINS AT ELLSWORTH AND SOUTHERN
0930 PM TSTM WND DMG 5 SSW PARADISE VALLEY 33.47N 111.98W
08/28/2008 MARICOPA AZ TRAINED SPOTTER
TREES DOWN 48TH ST AND MCDOWELL WITH 40 MPH WINDS
0938 PM TSTM WND GST 6 NW TEMPE 33.44N 112.01W
08/28/2008 M75.00 MPH MARICOPA AZ ASOS
MEASURED ASOS AT PHX AIRPORT
0940 PM HAIL 4 SW GUADALUPE 33.32N 112.01W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
32ND AND RAY
0940 PM HAIL 4 SW GUADALUPE 33.32N 112.01W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
0940 PM HAIL 4 SW GUADALUPE 33.32N 112.01W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
32ND AND RAY IN AHWATUKEE
1000 PM HAIL 4 SW GUADALUPE 33.32N 112.01W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
1010 PM TSTM WND GST 4 SSE PHOENIX 33.48N 112.05W
08/28/2008 M85.00 MPH MARICOPA AZ AMATEUR RADIO
MEASURED WIND GUST 16TH ST AND THOMAS
1015 PM TSTM WND GST WSW ESTRELLA 33.00N 112.42W
08/28/2008 M69.00 MPH MARICOPA AZ TRAINED SPOTTER
ESTRELLA PKWY AND ELLIOT
1015 PM DUST STORM 4 SW WADDELL 33.54N 112.41W
08/28/2008 MARICOPA AZ TRAINED SPOTTER
1/4 MI VIS IN DUST STORM 4 MI WEST OF LUKE AFB
1043 PM TSTM WND DMG 5 N AVONDALE 33.49N 112.36W
08/28/2008 MARICOPA AZ TRAINED SPOTTER
2 FOOT DIAM TREE DOWN
1101 PM HAIL 6 WSW FOUNTAIN HILLS 33.58N 111.84W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
FRANK LLOYD WRIGHT AND SHEA
1105 PM HAIL 5 NNE PARADISE VALLEY 33.61N 111.93W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
SCOTTSDALE AND THUNDERBIRD
1105 PM HAIL 3 S SCOTTSDALE 33.64N 111.86W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
104ST AND BELL
1130 PM HAIL 5 NNE PARADISE VALLEY 33.61N 111.93W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
SCOTTSDALE AND THUNDERBIRD
1130 PM HAIL 2 W PHOENIX 33.54N 112.10W
08/28/2008 E0.75 INCH MARICOPA AZ TRAINED SPOTTER
18TH AND GLENDALE
1130 PM TSTM WND DMG 2 W PHOENIX 33.54N 112.10W
08/28/2008 MARICOPA AZ TRAINED SPOTTER
18 INCH DIAM TREE DOWN
1140 PM HAIL 2 WSW PARADISE VALLEY 33.53N 111.98W
08/28/2008 E1.00 INCH MARICOPA AZ TRAINED SPOTTER
TATUM AND LINCOLN
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