*


All times are UTC + 1 hour



Post new topic Reply to topic
 [ 1 post ] 
Author Message
 Post subject: DOWNBURSTS - Deadly Wind
PostPosted: Thu Jul 07, 2005 5:04 pm 
Offline
Very Frequent Poster
User avatar

Joined: Mon Sep 24, 2001 1:00 am
Posts: 29533
Location: World (KF Admin)
A microburst claimed a kiteboarder in Utah recently. I understand that riders sometimes see the dust clouds from these violent weather phenomena kickup and act to depower their kites to try to avoid the high winds moving towards them. The kiteboarder in Utah wasn't aware of the microburst as might happen in other cases if the rider simply isn't looking in that direction. Downbursts can cause winds to gust into the 30 to almost 170 mph range. The wind velocity that you feel will be influenced by many factors including your distance from the burst, surface terrain, etc.. The writer was almost killed by a suspected wet microburst several years ago as well. This weather phenomena may have figured in other serious kiteboarding accidents. Downbursts have also caused a substantial number of airliner crashes.

Avoiding weather that generates downbursts would be a prudent step to take. If you google "the name of your country or state" and "microburst" you may well find record of past events in your area. These phenomena are very wide spread. It has been estimated that up to 5% of storms may be associated with downbursts.

Image 1.

Image2.

Which of the above two images is of tornado damage and which is of microburst damage?** See below for answer.

"During strong or severe thunderstorms, a burst of intense winds often flatten buildings and knock down trees. These winds, known as ‘downbursts’, are often mistaken for tornadoes due to the severity of the damage. A downburst features air diving toward the surface, whereas a tornado is composed of rising air."
From: http://www.usatoday.com/weather/ tg/wdnburst/wdnburst.htm

Image
A microburst felled this THREE TO FOUR FOOT DIAMETER HARDWOOD TREE. Worried about burst just messing your kite gear up?! Think again.

"Recall that a downburst is defined as strong downdraft with an outrush of damaging winds on or near the ground. Downbursts are subdivided based on their size. If the swath of damaging winds is 2.5 miles or greater in diameter, then it is termed a macroburst. If the swath is less than 2.5 miles, it is called a microburst. In general, microbursts are quick hitting events and are extremely dangerous to aviation. Microbursts are sub-classified as dry or wet microbursts, depending on how much or little rain accompanies the microburst when it reaches the ground."
From: http://spotterguides.us/advanced/advanced06.htm

Dry microbursts seem to be more prevalent in the interior states of the American west while the wet variety may be found in coastal areas.

Image
An animated gif of a burst.
From: http://www.exn.ca/news/images/1999/06/0 ... stanim.gif

Image

"Microbursts can occur anywhere convective weather conditions (thunderstorms, rain showers or virga) occur. Virga is rain that evaporates before it reaches the ground and is associated with a dry Microburst. Observations suggest that approximately five percent of all thunderstorms produce a microburst.

The Microburst can occur without rain ever reaching the ground as in the case of virga. The rain will evaporate and cause a cooling in the air, which causes the downdraft." Above is a diagram of a virga caused Microburst.

The life span of a Microburst is around 15-20 minutes. Here is a life cycle diagram of the Microburst.
From: http://www.math.unl.edu/~jfisher/NSF_96/windshear.html

An example of a four photo Dry Microburst appears at the link below. This one was associated with Virga and only put out winds estimated to be 50 kts. You can see the dust blown up on the ground associated with the down flow.

Image

CLICK HERE AND HIT SLIDESHOW

From: http://www.cimms.ou.edu/~doswell/microb ... tions.html


A good visual guide to severe weather appears at: http://www.abc.net.au/newcastle/stories ... 069538.pdf
A good reference on microbursts is at: http://www.cimms.ou.edu/~doswell/microb ... dbook.html
Another reference can be found at:
http://www.hprcc.unl.edu/nebraska/wind_events.html
and at:
http://www.ll.mit.edu/AviationWeather/wolfson.pdf



** Answer: Photo 1 is of microburst damage. Sometimes the outflow of microbursts in symmetical and linear resulting in the violent wind coming from one direction instead of several. Photo 2 is of tornado damage with a more caotic wind flow. Tornados can generate winds up to 300 mph, microbursts up to around 170 mph. The damage looks fairly similar.

FKA, Inc.

transcribed by;
Rick Iossi




WHAT TO LOOK FOR?

Check and carefully evaluate your local weather and weather hazard forecast before kiteboarding, ALWAYS.

Such as:

http://nws.noaa.gov/ (USA)
http://www.weatheroffice.com (Canada)
along with other various services in other countries. Learn what is available in your area and USE IT.


Some other ideas on weather planning can found at:
http://fksa.org/viewtopic.php?t=130

"Some of the clues but not necessarily all visual indications that a microburst may be forming are:

* Patches of virga mark potential microburst areas. As the precipitation evaporates, it cools the air and starts a downdraft. If the conditions are right, the downdraft may accelerate and reach the ground as a microburst. Localized areas or rings of blowing dust raised from the ground usually mark the impact point of dry microburst."

Image
Image
From: http://australiasevereweather.com/
Examples of virga, there are still other variations. Virga falling precipitation that evaporates before reaching the ground.

"* A small, intense, globular rain area, with an area of lighter rain in its wake, may mark a wet microburst. A rain foot, a marked outward distortion of the edge of the precipitation area, is usually a visual indicator of a possible wet microburst. As the microburst reaches the ground and moves away from its impact point, a plume of dust may be raised from the ground. This plume is called a dust foot and also marks a possible microburst."
From: http://spotterguides.us/advanced/advanced06.htm

Image
An example of a rain foot. From: http://ww2010.atmos.uiuc.edu/

Image
An example of a shelf cloud which can be accompanied by violent winds, tornados and microbursts. This photo was taken near the area of the snowkiteboarder fatality in Alberta, Canada on the same day.
From:
http://www.umanitoba.ca/faculties/envir ... /main.html

It is best to avoid kiteboarding when warnings of violent weather or downbursts have been made. The wet variety are not that uncommon with tropical weather systems, in feeder bands and other storm components. That is to say, THE HAZARD IN HURRICANES AND RELATED WEATHER IS HIGH! Feeder bands from hurricanes can be hundreds of mile long and can be filled with violent squalls. So even if the hurricane is a long distance from you a feeder band might be sweeping over your area.

Work to avoid downbursts. Reacting after they visually appear in your area is a fairly dangerous proposition.

FKA, Inc.

transcribed by:
Rick Iossi


{ SHARE_ON_FACEBOOK } { SHARE_ON_TWITTER } { SHARE_ON_ORKUT } { SHARE_ON_DIGG } { SHARE_ON_MYSPACE } { SHARE_ON_DELICIOUS }
Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic
 [ 1 post ] 

All times are UTC + 1 hour


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group