Guest

Virga - Why So Dangerous?

Thu Jul 12, 2001 1:49 am

Hey everyone

A couple of months ago, ny groudschool instrtor told me that if I could see virga I should be careful because it was very dangerous. But now I wonder, what is so different between virga and normal precipitations? It seems pretty much the same just that virga evaporates before reaching the ground.

So could anyone enlight me on why is virga so dangerous?

Regards,
Nicolas
 
sushka
Posts: 4657
Joined: Thu Nov 18, 1999 12:33 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 1:56 am

What is virga???
Pershoyu Spravoyu Litaki!
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 2:01 am

You must think about the process of evaporation in order to understand why it can be so dangerous.

Evaporation is a cooling process.

As the precip evaporates the air quickly cools and sinks as it becomes more dense than the surrrounding air.

This area of sinking air can create a microburst. Microbursts are associated with severe windshear and have caused catostrophic accidents.

The downward rushing air hits the ground and is forced upward allong the edges creating an area of rapid updrafts first and then a rapid and fatal sheear to a downdraft.

The larger the aircraft the more of an effect the windshear will have on it. This type of windshear in general is not something GA aircraft are affected by. But it should be a concern.

It is a definite concern for larger aircraft.

JET
 
JETPILOT
Posts: 3094
Joined: Tue May 18, 1999 6:40 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 2:03 am

Virga is precipitation that doesnt reach the ground. It evaporates as it falls.

Jsut a quick correction.....The virga we are talking about that is so dangerous is always associated with a hot summertime hot ambient temperature.

Virga associated with snow does not produce microbursts.

JET
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 2:23 am

Hi There. Well, the only thing I can think of... is that your instructor was WARNING you that, even though Virga dosen't obscure your vision "all" the way to the ground like regular types of precip does...DON'T be "tricked" into flying to close to it. It can change and move around just like any other curtain of rain or snow. So, if you're only VFR rated, and you wander to close to it, you could accidentally find yourself in IMC conditions and quickly become disoriented, which as you know, can be deadly!

Your instructor could also have been thinking about you getting caught up in the "Down Drafts" that are usually asociated with falling precip.

Sushka, like Nicolaki explained...Virga is simply precipitation that evaporates before it reaches the ground. Kinda like shear curtains that stop way above the carpet!  Big thumbs up

Hope this help.

Chris  Smile
"Just a minute while I re-invent myself"
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 3:05 am

JP posted some great info on the subject, and I'll add a couple of links that may better help you visualize things...

http://www.nssl.noaa.gov/~doswell/microbursts/Figure_04.JPG

When the microburst hits the ground, it spreads out in all directions, sorta like pouring water on a flat surface. Iy your aircraft happens to be underneath one while low/slow in the terminal area, it can get really ugly. The next link is the one that Delta 191 encountered before crashing at DFW in 1985: http://www.nssl.noaa.gov/~doswell/microbursts/Figure_07.JPG

Finally, microbursts come in two flavors; wet and dry:

http://www.nssl.noaa.gov/~doswell/microbursts/Figure_08.JPG

Each has their own specific dangers, i.e. the wet ones are shrouded in rain and often can't be seen (and avoided), while the dry ones are sometimes overlooked as threats, since yoy can't "see" a cold column of air descending towards the ground. Look for the dust on the ground. A Continental 727 encountered a dry one at Tuscon years ago, and while the outcome wasn't as bad as DL191, it sure could have been...

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
CX Flyboy
Posts: 6107
Joined: Sun Dec 26, 1999 6:10 pm

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 3:28 am

Viagra can be very dangerous to people with weak hearts, especially the elderly. Oh I see, you are talking about something else. Nevermind then. Big grin
 
flight152
Posts: 3357
Joined: Fri Nov 24, 2000 8:04 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 6:17 am

LOL CX flyboy  Laugh out loud
 
wannabe
Posts: 652
Joined: Wed Jun 30, 1999 3:37 am

RE: Virga - Why So Dangerous?

Thu Jul 12, 2001 7:29 am

Remember CX flyboy;
Vigra = down
Viagra = up

Seriously, I never heard of this until I read this post. Two years ago while flying into ORD from SWF on an AA F100, we were crossing Lake Michigan and there was virga all over the place (only I didn't know it was called that at the time). It was one rough ride. The pilot was trying to weave through the rain, but is was falling in many places yet you could see that it was not reaching the surface of the lake. Thanks to all for the information.

Who is online

Users browsing this forum: Google [Bot] and 30 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos