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A downdraft with horizontal extent of about 2.5 miles (4 kilometers) or less, associated with atmospheric convection, often a thundershower.
microburst extends from 3000 to 10,000 ft (1–3 km) and lasts from to 5 to 15 min. An intense microburst could induce wind speeds as high as 150 knots. Microbursts are normally associated with thunderstorms, but there are also “dry microbursts.” In these dry microbursts, precipitation falling from the thunderstorms into the relatively dry air of the lower atmosphere evaporates readily, and the large negative buoyancy thus produced accelerates the air downward, entraining more very dry air. No precipitation reaches the ground, but a microburst wind shear occurs. Airports equipped with an LLWAS (low-level wind-shear alert system) “network expansion,” LLWAS systems integrated with terminal Doppler weather radar (TDWR), and TDWR systems can detect microburst alerts and wind-shear alerts. Controllers will issue the appropriate wind-shear alerts or microburst alerts (e.g., “Runway 28 arrival microburst alert, 45 knot loss 3 mile final”).