Storm science

What is a microburst?

Not every "tornado" is a tornado. Some are microbursts — concentrated downdrafts that hit the ground with straight-line winds up to 150 mph.

The definition

A microburst is a small-scale, intense downburst — an area of sinking air producing damaging wind at the surface. Diameter: under 2.5 miles. Duration: 5-15 minutes.

Ted Fujita coined the term in 1975 after investigating an air crash at JFK.

The two types

Wet microburst

Downdraft accompanied by heavy rain. Common in humid climates. Cooling from evaporation drives descent.

Dry microburst

Rain evaporates before hitting ground. Very sudden wind onset. Common in high Plains and Southwest.

How they form

Precipitation aloft cools as raindrops evaporate.
Dense cold air descends rapidly.
At ground level, spreads out horizontally.
Impact zone: winds fan outward at 100+ mph.
Radial pattern of damage.
Individual microburst lasts 5-15 minutes.
Storm may produce multiple sequentially.

The aviation danger

Microbursts have killed hundreds in aviation.

1975 Eastern 66 (JFK) — Fujita's classic case.
1985 Delta 191 (DFW) — 137 dead. Modern radar improvements followed.
1994 USAir 1016 (Charlotte) — 37 dead.
FAA now requires Terminal Doppler Weather Radar (TDWR) at all major airports.
Predictive windshear alerts warn crews on approach.
Modern aircraft can execute go-around if microburst detected.

The damage pattern

Radial spread from central impact zone.
Trees fall AWAY from a common center (star or asterisk pattern).
Not rotational damage.
Sometimes mistaken for tornadoes.
NWS damage surveys distinguish based on debris pattern.
Straight-line winds different signature than rotational.

Microburst vs tornado

Rotation

Microburst: straight-line divergent. Tornado: rotating.

Damage pattern

Microburst: star / radial. Tornado: convergent / spiral.

Duration

Microburst: 5-15 min. Tornado: minutes to hours.

Path

Microburst: circular (2.5 mi max). Tornado: linear track.

Warning

Microburst: severe thunderstorm warning. Tornado: tornado warning.

Sound

Microburst: deep rumble. Tornado: freight train.

Detection

Doppler radar: convergence at surface.
Terminal Doppler at airports.
MRMS national mosaics.
Satellite: cloud-top cooling.
Ground observers: sudden temperature drop.
Airport wind sensors: rapid direction/speed change.

Notorious microbursts

1975 JFK Eastern 66 — 113 dead.
1985 DFW Delta 191 — 137 dead. Landmark for FAA policy.
1988 Cheektowaga NY — extensive damage.
1992 Blaine Washington — coastal microburst.
1994 Charlotte USAir 1016 — 37 dead.
2010 Wisconsin Family Circus Fair microburst — 2 dead.
2020 Iowa derecho — chained microbursts.
2023 Michigan concert microburst — Illinois State Fair (2011) precedent.

Safety

Severe thunderstorm warning = take shelter.
Do not stay in vehicle if warning tagged DESTRUCTIVE.
Interior room away from windows.
Watch for falling trees.
Downed power lines assumed live.
Aircraft: obey pilot for turbulence.
Boat: seek harbor.
Outdoor events: seek substantial shelter.

Everyday encounters

Small dry microbursts happen throughout Southwest US in summer.
Aircraft crews trained to recognize.
Public rarely notices except when trees fall.
Insurance treats as severe thunderstorm damage.
Damage often looks like tornado to untrained eye.