downburst

A downburst is a strong downdraft produced by a thunderstorm that, when it reaches the ground, sends out radial winds that can cause damage over a localized area. Downbursts are not tornadoes; they involve straight-line winds and a lifting gust front rather than rotating columns.

Downbursts are categorized by size and moisture: macrobursts are large-diameter downward drafts with wind damage over several kilometers; microbursts are small, intense downdrafts with a footprint less than about 4 kilometers across. Downbursts may be wet (air saturated with rain) or dry (precipitation evaporates into the descending column before reaching the ground).

Cause: Rain-cooled air from the storm becomes negatively buoyant and accelerates downward; as it hits the ground it spreads outward, sometimes generating a gust front that can drive damaging winds well beyond the updraft area. Evaporation of rain into dry mid-level air enhances cooling and downdraft strength.

Impacts: Downbursts can cause considerable damage to trees, structures, and vehicles; they are a major aviation hazard due to downdraft-associated wind shear, particularly during takeoff and landing.

Detection and forecasting: Weather radar can identify downburst signatures, such as a strong velocity couplet and a back-building gust front; surface weather observations and damage surveys help confirm events. Forecasting relies on analyzing environmental conditions, including lapse rates, moisture, and the presence of dry air aloft.