A microburst starts with a typical thunderstorm. What is a thunderstorm?
A thunderstorm works 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.
To understand the difference in the sizes of a Micro-burst and a Macro-burst I included another photo from WVVA TV.
A Microburst Storm is an intense, localized downdraft of air that spreads on the ground causing rapid changes in wind direction and speed. “downburst”
Microbursts are made of winds rushing down to the ground! Wind speeds can be 50- 100 mph, damaging roofs, snapping trees, etc…
Microbursts can happen so quickly here in Arizona and this is one reason why so many warnings are placed regarding flash floods. These intense storms are capable of producing winds of more than 100 mph causing significant damage.
On a positive note: Microbursts replenish the desert with much needed rain.