"Bob Gardner" wrote in message
...
If a cu has penetrated the freezing level, that's enough to scare me. We
get some dandies over the Cascades, Siskiyous, and Rockies.


Generally a cloud that penetrates minus-10 Celsius will produce
precipitation. But in cold weather it may do that in 4000 feet and be a
rather benign shower. When the cloud develops vertically through 25, 35, or
especially 45 thousand feet, however.... that's when it gets exciting.