e

T

0

4/20/23 

AIM 

FIG 7

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1

−

13 

Evolution of a Microburst 

Meteorology

HEIGHT (feet)

10,000

10,000 

5,000

5,000 

3

HE

IG

HT

(f

e

t)

WIND SPEED

WIND SPEED 

10-20 knots

10-20 knots 

> 20 knots

> 20 knots 

T-5 Min  T-2 Min 

T 

T + 5 Min

T + 5 Min

T-5 Min  T-2 Min 

T + 10 Min

T + 10 Min 

0 

1

2 

SCALE (miles)

SCALE (miles) 

Vertical cross section of the evolution of a microburst wind field. T is the time of initial divergence at 

the surface. The shading refers to the vector wind speeds. Figure adapted from Wilson et al., 1984, 

Microburst Wind Structure and Evaluation of Doppler Radar for Wind Shear Detection, DOT/FAA 

Report No. DOT/FAA/PM-84/29, National Technical Information Service, Springfield, VA 37 pp. 

c. 

The life cycle of a microburst as it descends in a convective rain shaft is seen in FIG 7

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1

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13. An important 

consideration for pilots is the fact that the microburst intensifies for about 5 minutes after it strikes the ground. 

d.  Characteristics of microbursts include: 

1.  Size. 

The microburst downdraft is typically less than 1 mile in diameter as it descends from the cloud 

base to about 1,000

−

3,000 feet above the ground. In the transition zone near the ground, the downdraft changes 

to a horizontal outflow that can extend to approximately 2 

1

/

2

 miles in diameter. 

2.  Intensity. 

The downdrafts can be as strong as 6,000 feet per minute. Horizontal winds near the surface 

can be as strong as 45 knots resulting in a 90 knot shear (headwind to tailwind change for a traversing aircraft) 

across the microburst. These strong horizontal winds occur within a few hundred feet of the ground. 

3.  Visual Signs. 

Microbursts can be found almost anywhere that there is convective activity. They may be 

embedded in heavy rain associated with a thunderstorm or in light rain in benign appearing virga. When there 

is little or no precipitation at the surface accompanying the microburst, a ring of blowing dust may be the only 

visual clue of its existence. 

4.  Duration. 

An individual microburst will seldom last longer than 15 minutes from the time it strikes the 

ground until dissipation. The horizontal winds continue to increase during the first 5 minutes with the maximum 

intensity winds lasting approximately 2

−

4 minutes. Sometimes microbursts are concentrated into a line structure, 

and under these conditions, activity may continue for as long as an hour. Once microburst activity starts, multiple 

microbursts in the same general area are not uncommon and should be expected. 

7

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1

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