Derecho

A shelf cloud along the leading edge of a derecho in Minnesota

A derecho (/ˈdɛrətʃoʊ/, from Spanish: derecho [deˈɾetʃo], 'straight')[1] is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system.[2]

Derechos cause hurricane-force winds, heavy rains, and flash floods. In many cases, convection-induced winds take on a bow echo (backward "C") form of squall line, often forming beneath an area of diverging upper tropospheric winds, and in a region of both rich low-level moisture and warm-air advection. Derechos move rapidly in the direction of movement of their associated storms, similar to an outflow boundary (gust front), except that the wind remains sustained for a greater period of time (often increasing in strength after onset), and may reach tornado- and hurricane-force winds. A derecho-producing convective system may remain active for many hours and, occasionally, over multiple days.

A warm-weather phenomenon, derechos mostly occur in summer, especially during June, July, and August in the Northern Hemisphere, or March, April, and May in the Southern Hemisphere, within areas of moderately strong instability and moderately strong vertical wind shear. However, derechos can occur at any time of the year. They are equally likely during day and night times.

Various studies since the 1980s have shed light on the physical processes responsible for the production of widespread damaging winds by thunderstorms. In addition, it has become apparent that the most damaging derechos are associated with particular types of mesoscale convective systems that are self-perpetuating (meaning that the convective systems are not strongly dependent on the larger-scale meteorological processes such as those associated with blizzard-producing winter storms and strong cold fronts). In addition, the term "derecho" sometimes is misapplied to convectively generated wind events that are not particularly well-organized or long-lasting. For these reasons, a more precise, physically based definition of "derecho" has been introduced within the meteorological community.[3][4]

  1. ^ The dictionary definition of derecho at Wiktionary
  2. ^ Cite error: The named reference noaafacts was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference BAMS-D-14-00254.1 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference 2024Definition was invoked but never defined (see the help page).