Microburst

A microburst is a small, very intense downdraft that descends to the ground resulting in a strong wind divergence. The size of the event is typically less than 4 kilometers across. Microbursts are capable of producing winds of more than 100 mph causing significant damage. The life span of a microburst is around 5-15 minutes.

When rain falls below cloud base or is mixed with dry air, it begins to evaporate and this evaporation process cools the air. The cool air descends and accelerates as it approaches the ground. When the cool air approaches the ground, it spreads out in all directions and this divergence of the wind is the signature of the microburst. In humid climates, microbursts can also generate from heavy precipitation.

Pronunciation: my-crow-burst

Also Known As: downburst

Examples:

A downburst is defined as a strong downdraft with an outrush of damaging winds on or near the ground. If the swath is less than 2.5 miles, it is called a microburst. Microbursts are quick-hitting events and are extremely dangerous to aviation. Microbursts are sub-classified as dry or wet microbursts, depending on how much rain accompanies the microburst when it reaches the ground.

The evolution of downbursts is broken down into three stages: the contact stage, the outburst stage and the cushion stage.

* A downburst initially develops as the downdraft begins its descent from cloud base. The downdraft accelerates and within minutes, reaches the ground (contact stage). It is during the contact stage that the highest winds are observed.

* During the outburst stage, the wind "curls" as the cold air of the downburst moves away from the point of impact with the ground.

* During the cushion stage, winds about the curl continue to accelerate, while the winds at the surface slow due to friction.[6]

A microburst is a very localized column of sinking air, producing damaging divergent and straight-line winds at the surface that are similar to but distinguishable from tornadoes which generally have convergent damage. There are two types of microbursts: wet microbursts and dry microbursts. They go through three stages in their life cycle: the downburst, outburst, and cushion stages. The scale and suddenness of a microburst makes it a great danger to aircraft due to the low-level wind shear caused by its gust front, with several fatal crashes having been attributed to the phenomenon over the past several decades.