PHOENIX METRO MACROBURST - 1996
Thunderstorms are a common occurrence during the Arizona Monsoon; on any given day scattered storms are possible across the southern deserts and many of them can produce strong, gusty winds, along with heavy rain and small hail. In some instances, the downdrafts associated with the thunderstorms are very strong, but very localized, with damaging winds reaching from 60 to over 80 mph. Winds such as these are known as "microbursts", as they only last for a short time, and affect a small area.
On a much larger scale, in both time and space, there is the phenomenon known as the "MACROBURST". This is sort of like the "big brother" to the microburst. The strong, rain-cooled downdrafts from the monsoon thunderstorms become well organized and persistant, and can last for a much longer time, and cover a much greater area. One such notable macroburst affected the Phoenix metropolitan area on August 14 of 1996. In this case, strong thunderstorms between Paradise Valley and Crown King organized into a massive cluster of storms in the vicinity of Carefree; this cluster of storms marched rapidly southwestward across the west valley, producing widespread damaging winds and very heavy rainfall. Peak wind gusts of up to 115 mph were measured at the Deer Valley Airport, and the storm caused over 160 million dollars of damage over several west valley cities, including Buckeye. The measured speed of 115 mph set the all time peak gust record record for Phoenix, as well as for the entire state of Arizona!
It should be noted that macroburst winds, unlike tornadic winds, are STRAIGHT-LINE winds - they do not contain strong rotation such as would be observed with the passing of a tornado. These strong winds descend from the lower levels of a thunderstorm, then hit the ground and spread outwards, moving in a straight line.
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This image shows the severe storm in its incipient stages. At 00:38 GMT (5:38 pm MDT), a cluster of strong thunderstorms was beginning to organize, with the main cells located between Crown King and Fountain Hills. This cluster will continue to coalesce into a Mesoscale Convective System (MCS). |
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At 01:02 GMT, the MCS has developed in the vicinity of New River, Carefree and Cavecreek. |
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At 01:20 GMT the system has started to move southwestward into the northern and northwestern portions of the Phoenix Metropolitan area. As it moves to the SW, it will generate very strong, straightline winds which push out ahead of the system. These strong "macroburst" winds, will reach speeds of up to 115 mph...as recorded at the Deer Valley airport. |
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At 01:37 GMT, the MCS continues to propogate quickly to the southwest, moving through the western portions of the metro area. It can be seen moving through Peoria and Sun City, among other places. |
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This last image, taken at 02:01 GMT (7 pm), shows a well defined, leading edge to the system, moving quickly southwestward ahead of the main storm cluster and through the West Valley communities, such as Buckeye. The radar reflectivities seen with this MCS are intense, and associated with copious rainfall, as well as small to moderate hail...which accompanied the severe and damaging winds that lashed the west valley communities. |