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96-97 SW/E A
wide view of this LP supercell shows the entire storm - from the high-based
compact core to the flaring anvil above. Rain and hail are falling overhead
and to the right, but are not heavy enough to block the light. There were rumbles
of thunder but not a single bolt! A slender F0-F1 tornado (see closeup in 97)
lifted and reformed repeatedly for 20 minutes but never had any signs of a wall
cloud above it. Although the anvil was streaming by above, the main updraft
remained almost in the same location for an hour due to extreme regeneration
at the back of the storm.
A significant distinction must be made between a tornado as a visible funnel
extending to the ground and the associated violently rotating column of air.
When we see a tornado we are usually looking at its condensation funnel, a cloud
condensed in the very low pressure within the vortex. However, many tornadoes
have short or incomplete condensation funnels and some none at all. This can
fool us into thinking the tornado hasn't reached the surface. A tornado can
be doing major damage (often made visible by the debris cloud at the ground)
with few visible signs of its presence in the sky above.
Stages in tornado development
Most tornadoes and funnel clouds will be preceded by a rotating wall cloud.
You can see the rotation by watching the bits of cloud along the edge of the
lowering moving slowly around it. The motion is usually clockwise when looking
up.
If the entire wall cloud rotates faster and lowers further,a large,wide tornado
can form without a typical funnel. However, most cases will have a funnel cloud
form under the wall cloud, usually between the centre and south edge of it.
The funnel will be smooth-edged and tapered to a point. Some larger funnel clouds
may appear as a rounded bulb or diffuse V-shaped cone.
If the funnel is wide or close to the ground it is likely already a tornado
and you should check carefully for debris. Thinner funnel clouds may hang in
the air for several minutes, then disappear again. If they lengthen downward
it will only be a minute or two before ground contact is made. But it must
be stressed that a tornado can exist without a long funnel or any signs of rotation
in the air. Indeed, often the first visible sign of a tornado touchdown is a
cloud of debris at the ground.
![Please click on the image for a larger version](/web/20060208015406im_/http://www.msc-smc.ec.gc.ca/education/severe_weather/sm_images_e/page35_2.jpg)
98-99 NW/E The SW back end of this classic supercell
has a small, circular wall cloud and F2 tornado. The funnel is a mere rounded
bulbous extension, but the vortex is obvious from the large debris cloud being
stirred up. After 5 minutes (99), the tornado has lifted (no more debris visible)
even though the condensation funnel is now much longer.
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Created :
2002-08-26
Modified :
2002-12-19
Reviewed :
2002-12-19
Url of this page : http://www.msc.ec.gc.ca /education/severe_weather/page35_e.cfm
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