Re: Funnel clouds vs tornadoes

[Glenn Rivers]

Whoops...ignore this, see below.

 

[Glenn Rivers]

Funnel cloud = A condensation funnel extending from the base of a towering cumulus or Cb, associated with a rotating column of air that is not in contact with the ground (and hence different from a tornado). A condensation funnel is a tornado, not a funnel cloud, if either a) it is in contact with the ground or B) a debris cloud or dust whirl is visible beneath it.

Tornado = A violently rotating column of air in contact with the ground and extending from the base of a thunderstorm. A condensation funnel does not need to reach to the ground for a tornado to be present; a debris cloud beneath a thunderstorm is all that is needed to confirm the presence of a tornado, even in the total absence of a condensation funnel.

I agree with the above statement, but when one sees a condensation funnel reaching part way to the ground, how does one now if it is a funnel cloud or a tornado?...how does one know if it is in contact with the ground? About damage....what if there is nothing to damage. There will be cases where it is not possible to determine whether the vortex associated with a partly condensed condensation funnel reaches the ground or not.

The operational definitions of tornadoes vs. funnel clouds are all well and good, but often it will be visually impossible to distinguish between the two until after the fact if at all. Dust whirls? Helpful, but don't count on that clue if the ground is wet and vegetation covered. Damage? Very helpful, but if no trees or buildings are in the path, it may never be possible to determine if a vortex was on the ground.

It is also important that the public not think that a tornado is not dangerous because it only condenses part way to the ground.

 

[Andy Wehrle]

http://en.wikipedia.org/wiki/Funnel_cloud

This was an article I made for Wikipedia after noticing they didn't have an entry for "funnel cloud"

 

[Greg Stumpf]

I originally posted this in:

http://www.stormtrack.org/forum/viewtopic....ighlight=#27321

"Actually, technically, a funnel cloud is not a "tornado aloft". A funnel cloud is merely an accessory to a rotating vortex of wind. Caused by the rapid drop of pressure in the vortex, cloud drops will condense to form the funnel cloud. The amount of condensation is a factor of the relative humidity (RH) in the vortex column (which can be variable with height), and the pressure drop. Think of it as a local pressure deficit under an updraft base, and localized area where the LCL is lower. Thus, many high plains (low RH) tornadoes will not have condensation to the ground, and the tornadic winds can exist in the vortex outside the edge of condensation. Conversely, many East Coast and Gulf Coast (high RH) tornadoes may have condensation that occurs outside the edge of the damaging winds.

There is also considerable debate as to whether or not tornadoes form aloft and the "touch down" even in supercell tornadoes. Nonetheless, when tornadic vortices strengthen, the pressure drops, and thus the funnel cloud (or LCL) lowers with time, and appears to "touch down". This can occur even with non-supercell tornadoes that spin up from the ground."

Furthermore, if you observe a funnel cloud without debris, most likely either 1) there is a ground circulation but it is still too weak to cause damage and/or loft debris, or 2) you are not in a good position to see a ground circulation or debris (which might be shallow).

 

[Greg Stumpf]

http://en.wikipedia.org/wiki/Funnel_cloud

This was an article I made for Wikipedia after noticing they didn't have an entry for "funnel cloud"

So, anyone can make a Wikipedia entry? That concerns me!

Case in point:

Mesocyclones are convection vortices formed in powerful thunderstorms, which generate many dangerous byproducts. They are most commonly observed in supercell thunderstorms, but they can drive the activity of lesser thunderstorms as well.

A mesocyclone generates many effects as a result of the mixing of warm updrafts, and cold downdrafts. The main effect is hail, which is almost always present if a mesocyclone has formed. The hail generates powerful lightning bolts. Other effects of a mesocyclone include powerful downdrafts, which can take down an aircraft, strong wind shear, and torrential downpour.

The most severe side-effect of the mesocyclone occurs when a downdraft and the flanking line of the mesocyclone collide. The first effects will be a "mammatus", or a bubbly cloud formation. If the downdraft is strong enough, the flanking line will lower and produce a "wall cloud". The final result is the formation of funnel clouds and finally tornadoes.

 

[Glen Romine]

Wow Greg - that is horrible!!! Fortunately though - it can be fixed. Wikipedia relies on someone with expert knowledge to come along and fix errors such as these. But this certainly drives home the point that it is a questionably accurate source of information.

The same person might have done the thunderstorm entry as well:

The supercell possesses a mesocyclone, the results of which are strong vertical shear, differences in wind speed at different layers and separate updraft and downdraft regions, with the effect being that the storm will both last longer and continue to grow larger and more dangerous.

http://en.wikipedia.org/wiki/Thunderstorm

If you or someone else wants to fix some of these entries:

http://en.wikipedia.org/wiki/Wikipedia:How..._to_edit_a_page


Andy, perhaps you could update your funnel cloud definition based on the information Greg provided.

Glen

 

[Robert Dewey]

While there is a distinct difference between the two, I think the public should be just as concerned with a funnel cloud (i.e. no ground circulation) as they are with an actual tornado - You just never know when a ground circulation will develop. A visible condensation funnel need not touch the ground for it to be a tornado, but a ground circulation must be present, obviously.

Actually, my avatar is a good example... While that appears to be just a funnel cloud, it did in fact have a ground circulation (which you can't see because of too many objects). According to the NWS, it caused a relatively small area of F1 damage...