The Denver Convergence Vorticity Zone (DCVZ) is an

orographically Orography is the study of the topographic relief of mountains, and can more broadly include hills, and any part of a region's elevated terrain. Orography (also known as ''oreography'', ''orology'' or ''oreology'') falls within the broader discip ...

-induced atmospheric phenomenon characterized by convergent winds in the

High Plains High Plains refers to one of two distinct land regions: *High Plains (United States), land region of the western Great Plains * High Plains (Australia), land region adjacent to the Great Dividing Range See also * Altiplano (disambiguation) The ...

just

east East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth. Etymology As in other languages, the word is formed from the fa ...

of the

Denver Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the United ...

metropolitan area, typically in length and oriented in a north-south direction. This meteorological feature was subject to scientific scrutiny following a large outbreak of Denver-area

tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, alt ...

es in 1981 and is implicated in the propensity of the area to spawn

landspout __NOTOC__ Landspout is a term created by atmospheric scientist Howard B. Bluestein in 1985 for a kind of tornado not associated with a mesocyclone. The ''Glossary of Meteorology'' defines a landspout as : "Colloquial expression describing tor ...

(

misocyclone Tornadogenesis is the process by which a tornado A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often ...

) and

supercell A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. Due to this, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms ...

(

mesocyclone A mesocyclone is a meso-gamma mesoscale (or storm scale) region of rotation (vortex), typically around in diameter, most often noticed on radar within thunderstorms. In the northern hemisphere it is usually located in the right rear flank (bac ...

) tornadoes. The DCVZ is often associated with the

Denver Cyclone Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the United S ...

effect, which some consider as a more fully developed iteration of the DCVZ, although the Denver Cyclone is considered a distinct atmospheric phenomenon by some scientists.Pietrycha, A. Email correspondence quoted by Sam Barricklow, http://www.k5kj.net/DCVZ.htm

Characteristics

DCVZ conditions form when a low-level moist, southeasterly flowing

air mass In meteorology, an air mass is a volume of air defined by its temperature and humidity. Air masses cover many hundreds or thousands of square miles, and adapt to the characteristics of the surface below them. They are classified according to ...

meets the

Palmer Divide Named after Colorado Springs founder William Jackson Palmer, the Palmer Divide is a caprock escarpment style ridge in central Colorado that separates the Arkansas River basin from the South Platte basin. It extends from the Front Range of the Rock ...

, a ridge that extends east of the Colorado Front Range. If the moist air lifts over the ridge and meets northwesterly winds originating in the

Rocky Mountain The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

foothills, winds may converge to create enhanced cyclonic

vorticity In continuum mechanics, vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point (the tendency of something to rotate), as would be seen by an observer located at that point and traveling along w ...

. A study conducted between 1981 and 1989 demonstrated that the DCVZ formed on one-third of all days during the

convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

season (May through August). DCVZ conditions are often associated with the Denver Cyclone effect, which is characterized by the formation of a large

gyre In oceanography, a gyre () is any large system of circulating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determin ...

near the city center.

Role in atmospheric convection and tornado formation

When a DCVZ and especially Denver Cyclone develop, an otherwise

capped In sport, a cap is a player's appearance in a game at international level. The term dates from the practice in the United Kingdom of awarding a cap to every player in an international match of rugby football and association football. In the ea ...

atmosphere devoid of deep, moist

atmospheric convection 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 ...

(e.g. thunderclouds) may break into

cumulonimbus Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...

and

cumulus congestus cloud Cumulus congestus clouds, also known as towering cumulus, are a form of cumulus that can be based in the low or middle height ranges. They achieve considerable vertical development in areas of deep, moist convection. They are an intermediate stage ...

s. Once initiated these thunderclouds may form very rapidly. Dry microbursts and landspouts may occur in the early stages of development whereas wet microbursts and occasionally mesocyclonic tornadoes during later stages. All of these are recognized as fairly common and as hazards for

Denver International Airport Denver International Airport , locally known as DIA, is an international airport in the Western United States, primarily serving metropolitan Denver, Colorado, as well as the greater Front Range Urban Corridor. At , it is the largest airport in ...

(DIA), both the former location at Stapleton and the newer location farther east. Various measures were adopted to identify these hazards and take action to mitigate when present. Many studies document the role of the DCVZ in

tornado outbreak __NOTOC__ A tornado outbreak is the occurrence of multiple tornadoes spawned by the same synoptic scale weather system. The number of tornadoes required to qualify as an outbreak typically are at least six to ten, with at least two rotational ...

s across the Denver area. Using climatic data from the 1980s, one researcher suggested that the presence of a strong June DCVZ is associated with a 70% chance of zone-area tornado

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

.Szoke, E.J., and J.A. Augustine, 1990: A decade of tornado occurrence associated with a mesoscale flow feature: The Denver Cyclone. 16th Conference on Severe Local Storms, Alberta, Canada, American Meteorological Society, 554-559.

References

External links

A Subsynoptic Analysis of the Denver Tornadoes of 3 June 1981

(Albert E. Pietrycha and Erik N. Rasmussen)
Discussion of Boulder Tornado Touchdown - June 1997
{dead link, date=January 2018 , bot=InternetArchiveBot , fix-attempted=yes Atmospheric dynamics Regional climate effects Geography of Colorado Geography of Denver Denver metropolitan area