Near Santa Rosa, Photo by Leah Robertson
 

 

Downburst winds are a common byproduct of thunderstorms that affect New Mexico during the Summer Monsoon and are extremely hazardous. They, along with flash floods, are the two thunderstorm-related weather hazards most likely to produce property damage in the State of New Mexico.

A downburst is a non-rotating wind that is created by a column of sinking air in a thunderstorm that, after hitting ground level, spreads out in all directions and is capable of producing damaging straight-line winds of over 100 mph. These winds can often produce damage similar to, but distinguishable from, that caused by tornadoes.

 
Albuquerque Golf Course, Photo by Keith Hayes

The physical properties of a downburst are completely different from those of a tornado. Often the damage is very localized, as in the photo above, or in some cases, can be widespread. This tree and a few others were uprooted on a golf course after thunderstorm downburst winds occurred. However, most of the trees in the golf course were not damaged.

When rain descends from a thunderstorm, evaporative cooling and drag act to strengthen the downward velocity of the downdraft. At times, the precipitation will evaporate prior to reaching the ground. Once the accelerating air reaches the ground, it will spread laterally, often with a vortex or "curl" on the lead edge. Downburst damage will radiate from a central point as the descending column spreads out when impacting the surface, whereas tornado damage tends toward convergent damage consistent with rotating winds.

 On June 19 of 2010, a local photographer was able to capture a microburst event associated with shallow convection and virga during sunset in Albuquerque (lower left). The beauty of the photograph can be misleading - as these virga showers are producing strong downburst winds. The local observation at the Albuquerque Sunport reported a peak gust of 57 mph.  Around the same time, a large fuel tank under construction near the airport sustained extensive damage from the microburst winds (lower left).

 photograph of virga producing strong microburst winds  photograph of damaged tank from microburst winds
Photo by Leah Robertson Photo courtesy of Gene Jaramillo

To differentiate between tornado and downburst damage, an assessment is completed post-storm of the affected areas in order to determine the type of impact the winds had on structures and vegetation. If a downburst is found to have occurred, and the area impacted with 2.5 mi or less, it is termed a Microburst, whereas if the impacted area is greater than 2.5 mi, it is then termed a Macroburst.

The manifestation of downburst winds is often visible on radar imagery as arc-shaped images that move away from thunderstorms. As the winds spread away from the parent thunderstorms, the leading edge of the winds, also known as an "outflow boundary" or "gust front", often denote the presence of strong winds and potential areas to monitor for new storm formation. The winds that are associated with these features are also referred to as "straight-line winds."

In the image to the right, outflow boundaries are evident to the southeast of the strongest thunderstorms, but there are also outflow boundaries associated with cells not visible on the image. Not all outflows are strong enough to do damage.

Although difficult to see in this image, downburst winds in New Mexico can often result in stong surface winds that produce areas of blowing dust. In the photo to the left, the downdraft of the thunderstorm (in the center  of the image) has produced high winds and an area of dust (right side of the downdraft at the surface). In addition to wind damage, downburst winds can produce local dust storms that can reduce visibilities to near zero in less than a minute.

Albuquerque, Photo by Earl Breon  
 
 

 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 2.5 miles in extent: these are called microbursts. Downbursts larger than 2.5 miles in extent are sometimes called macrobursts. Downbursts can occur over large areas. In the extreme case, a derecho (a widespread and long-lived, violent convectively induced straight-line windstorm that is associated with a fast-moving band of severe thunderstorms in the form of a squall line) can cover a huge area more than 200 miles wide and over 1000 miles 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.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.