Monsoon Season in Phoenix and Tucson, Arizona – a Microburst starts with a typical thunderstorm. What is a thunderstorm? Thunderstorms work like an engine. It pulls moisture and air in and converts it to rain and then pushes wind and rain out. For the thunderstorm to continue; it has to be TILTED. The top of the thunderstorm can NOT be directly over the bottom.
During the later months of Arizona Monsoon (which means a season – like summer is a season), the steering flow in the upper-level of the atmosphere weakens. The UPPER level winds are what tilt storms, such as thunderstorms. The thunderstorm can still form but it will lose the tilt quickly!
This picture is the basics of a thunderstorm. The updrafts and downdrafts are made up of warm air and cooler air.
(Photo of a Thunderstorm chart courtesy of WVVA TV in Virginia – http://www.wvva.com/ )
As warm, humid air rises inside a storm, heavy rain forms and some of it evaporates in the colder air on top. This cooled air then sinks, accelerates and spreads out as it hits the ground, resulting in a localized, wind called a microburst.
These down bursts are put in two categories. A MACRO-burst and MICRO-burst, only difference is the area they are concentrated in.
This photo I included is a smaller area Micro-Burst that I was watching yesterday from our driveway, in southeast Arizona, outside of Tucson.
To understand the difference in the sizes of a Micro-burst and a Macro-burst I included another photo from WVVA TV.
Standing in our driveway, I continued to watch the Microburst hoping it wasn’t coming our way. It was moving quickly to the South and growing in size! Here is a picture of the Microburst – possibly now a Macroburst from July 10, 2012.
Microbursts are very dangerous for aircraft.