page_title: Atmospheric convection
section_title: Downburst
hierarchical_section_title: Atmospheric convection / Concerns regarding severe deep moist convection / Downburst
caption_attribution_description: English: Cumulonimbus calvus cloud over the Gulf of Mexico in Galveston, Texas
context_page_description: Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.
context_section_description: A downburst is created by a column of sinking air that, after hitting ground level, spreads out in all directions and is capable of producing damaging straight-line winds of over 240 kilometres per hour (150 mph), often producing damage similar to, but distinguishable from, that caused by tornadoes.  This is because the physical properties of a downburst are completely different from those of a tornado.  Downburst damage will radiate from a central point as the descending column spreads out when impacting the surface, whereas tornado damage tends towards convergent damage consistent with rotating winds.  To differentiate between tornado damage and damage from a downburst, the term straight-line winds is applied to damage from microbursts.
  Downbursts are particularly strong downdrafts from thunderstorms.  Downbursts in air that is precipitation free or contains virga are known as dry downbursts; those accompanied with precipitation are known as wet downbursts.  Most downbursts are less than 4 kilometres (2.5 mi) in extent: these are called microbursts.   Downbursts larger than 4 kilometres (2.5 mi) in extent are sometimes called macrobursts.   Downbursts can occur over large areas.  In the extreme case, a derecho can cover a huge area more than 320 kilometres (200 mi) wide and over 1,600 kilometres (990 mi) long, lasting up to 12 hours or more, and is associated with some of the most intense straight-line winds, but the generative process is somewhat different from that of most downbursts.
caption: Cumulonimbus cloud over the Gulf of Mexico in Galveston, Texas
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