(meteorobs) mammatus clouds do precede tornadoes

[CanisDirus57 at aol.com]

Lenticular clouds are pretty common in mountainous areas as they are formed 
from the forced ascent of air flowing over mountains. The moisture in the 
airstream condenses into a cloud at a certain point in the wake flow over and 
around the mountain and even though the air is moving, the cloud stays in one 
spot...hence the term "standing wave cloud" for lenticular clouds. There's a really 
impressive photo of one such cloud over Mount Fuji in Japan at this site:

http://faculty.whatcom.ctc.edu/dmckeeve/classes/Winter_classes/150/150res.htm

Mammatus are usually associated with thunderstorms, including supercell 
thunderstorms,  which are the ones that produce strong tornadoes. It depends what 
your vantage point is, how strong the thunderstorm is, and what direction the 
storm is moving as to whether  or not you have to worry about getting hit by a 
tornado after you see mammatus clouds. The majority of times I have seen 
mammatus, the storm passed many miles from me without even bringing a drop of rain.