What Is a Microburst, and What Makes It So Dangerous to Aircraft?

What Exactly Is a Microburst?

A microburst is a small, intensely concentrated downdraft produced by a convective cell — essentially a column of air descending with tremendous force from a thunderstorm or convective cloud. When that column of sinking air strikes the surface, it has nowhere to go but outward, spreading in all directions like water from a faucet hitting a flat surface. Despite its destructive power, a microburst is surprisingly compact. Its horizontal extent is typically less than 2 miles, and the event itself usually lasts only 5 to 15 minutes from start to finish. The Aviation Weather handbook, FAA-AC-00-6, covers microbursts in its Wind Shear chapter, and for good reason — the wind shear a microburst produces is unlike almost anything else a pilot can encounter in flight.

One critical detail that catches many student pilots off guard: a microburst can continue to intensify for up to 5 minutes after precipitation has completely stopped at the surface. That means the most dangerous phase of a microburst may arrive after the visible rain has already moved on — a fact that has lethal implications for situational awareness.

The Wind Shear Sequence That Makes Microbursts Lethal

Many student pilots make the mistake of thinking a microburst is simply a very strong gust of wind. It is not. What makes a microburst uniquely deadly is the structured sequence of wind shear it forces an aircraft through — and that sequence is specifically punishing during the two most critical phases of flight: approach and departure.

Picture an aircraft flying into a microburst on final approach. The first encounter is with a strong headwind on the leading edge of the outflow. This headwind increases airspeed and creates a pitch-up tendency, which can feel deceptively positive to the pilot. The natural instinct — or the autopilot response — is to reduce power and pitch down to maintain the glidepath. Then, within seconds, the aircraft enters the core downdraft itself, where vertical speeds can reach a staggering 6,000 feet per minute. Finally, as the aircraft punches through to the trailing edge, it hits a powerful tailwind. Airspeed drops sharply. Lift collapses. The aircraft is now low, slow, and sinking — and the transition from that false headwind boost to the tailwind penalty can happen faster than a pilot can diagnose and respond, even with full power applied.

Surface winds beneath a microburst can exceed 45 knots, and in extreme cases peak surface winds have been measured above 100 knots. That figure alone should recalibrate any instinct to underestimate this phenomenon. The performance demands placed on the aircraft during the tailwind phase routinely exceed what the airframe and engine can overcome at low altitude, which is why microburst encounters have resulted in fatal accidents involving transport-category aircraft with far more power than a typical training airplane.

Dry Microbursts and the Virga Threat

Perhaps the most insidious form of microburst is one you cannot easily see coming. A dry microburst occurs when precipitation evaporates entirely before reaching the surface — a phenomenon visible as virga, the streaks of rain or ice crystals hanging beneath a cloud base that disappear before touching the ground. In arid or semi-arid regions, dry microbursts are relatively common, and their danger lies precisely in their invisibility. There is no rain shaft, no visible curtain of precipitation to warn a pilot that a downdraft is occurring beneath that cloud.

Virga is a visual cue worth taking seriously. If you observe streaks of precipitation beneath a convective cloud that are not reaching the surface, treat the area below that cloud as potentially hostile airspace. The evaporation process that creates virga actually intensifies the downdraft by cooling and densifying the air — which means a dry microburst can be just as violent as one associated with heavy rain, while offering far fewer visual warning signs.

What Your DPE Wants to Hear on the Checkride

When your designated pilot examiner asks about microbursts, a strong answer covers four things: the definition of a downdraft that spreads outward upon reaching the surface, the three-phase wind shear sequence of headwind, downdraft, and tailwind, the specific performance numbers that convey the severity, and the concept of dry microbursts associated with virga. Connecting those dots — rather than simply calling it a strong wind — demonstrates the kind of meteorological understanding that earns confidence from an examiner.

You should also be able to explain why low altitude matters so much. The same wind shear sequence at cruise altitude would be uncomfortable; on short final at 200 feet above ground level, it is unrecoverable. That context is what transforms a textbook definition into genuine aeronautical decision-making knowledge.

Microbursts sit at the intersection of weather theory and real-world pilot judgment, which is exactly why they appear on checkrides. Knowing the numbers, understanding the mechanism, and respecting the hidden forms like virga-driven dry microbursts will demonstrate checkride-ready meteorological competence.

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