[BC] Rotation, Funnel Clouds, and Tornados

[Frederick W. Seibold]

Each March (Severe Weather Month) the NWS runs a WX spotter school near 
you, at least in the midwest.  It's worth your 2-3 hours.  Since the 
widespread deployment of doppler radars, a lot has been learned about 
tornado formation.  If the radar sees rotation, NWS will issue a 
warning.  This is a result of the Plainfield, IL, tornado of a few years 
back in which there was no warning before and big lawsuits afterward.  The 
problem is the line-of-site propagation we know so well.  After a few miles 
from the radar site, the radar cannot see to the ground, (line of sight is 
above ground, maybe a mile or more) so the radar has no way of knowing if 
it is a funnel cloud (aloft) or a tornado (on the ground).  Tornados are 
not aloft; if aloft, it is a funnel cloud.  A tornado is a funnel cloud in 
contact with the ground.  It is very difficult to spot (on the ground) 
either the funnel cloud or the tornado, at night and/or in heavy 
rain.  That a funnel cloud has touched the ground and become a tornado 
almost always has to be confirmed by a spotter on the ground.  As Rod 
Palmer, long-time recently retired Warning Meteorologist for the NWS in 
central Illinois, emphasized at these yearly events (I've been to a few): 
"If it doesn't spin, don't call it in."  Straight-line winds from heavy 
thunderstorms are often mistaken for "tornadoes".

73

Fred W9FWS  


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