METEOROLOGIST JEFF HABY
Tornadoes are one of the more spectacular weather phenomena to observe in the field. There are other weather phenomena that can be confused
with a tornado. Four of these that will be discussed include rain/hail shafts, scud, dust devils and gustnadoes.
To be a tornado, the circulation must be produced and directly connected to a convective cloud and the circulation must be in contact with
the ground. The rain/hail shaft and scud are not a tornado since they do not have a tornadic circulation while dust devils and gustnadoes
are not tornadoes since they are not in direct contact with the convective cloud. In the case of dust devils, often no convective cloud
is present at all.
Rain/hail shafts can be confused with a tornado since they can look like a dark extension from the thunderstorm to the ground. Typically a tornado
will occur in the updraft region of the storm while the heavy rain/hail shaft will be in the downdraft region of the storm. Sometimes the
heavy rain and hail can wrap around the tornadic circulation which produces that is called a rain wrapped tornado. In these cases the
heavy rain and hail can hide the tornadic circulation. However, if there is only a rain/hail shaft with no tornadic circulation then
it is not a tornado. Radar data and trained storm observers can help aid in determining if the rain/hail shaft has an embedded tornadic
circulation or not.
Scud can be confused with a tornadic circulation since they are clouds that can be very close to the ground and scud move quickly with the
low level wind. The dark clouds of the scud can be confused with a tornadic circulation extending from the cloud to the ground. A difference
between scud and a tornadic circulation is that the scud will tend to move more linearly while a tornado will exhibit a circulation pattern.
Scud can occur in the presence of a tornado thus radar data and trained storm observers can help aid in determining if both scud and a
tornado are present or if it is just scud.
A dust devil can exhibit a circulation on the ground but since it is not associated with a convective storm, it is not a tornado. A dust devil
typically also has weaker winds than a tornado.
A gustnado can have a circulation of wind on the ground with an associated thunderstorm nearby but there is not a direct connection between
the gustnado and the convective storm. Typically the gustnado will form along an outflow boundary. The diagram below in the lower right
shows an outflow boundary coming out of a thunderstorm with a gustnado spinning up along the edge of the outflow boundary.