microburst

The strong downdraft that spreads horizontally just above the ground to form a sharply defined gust front. An aircraft approaching this microburst or gust front may encounter a headwind followed by a strong downdraft and finally end up with a strong tailwind. The area of 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”).

An aircraft flying from A to F will experience strong headwinds at positions A and B. It will experience increasing tail winds at position D and E. There would be downdraft at positions B, C, and D. The maximum intensity of downdraft will be at position C.