"Icebound" wrote in message
...

Snip


I chose the definition from the Canadian Manual of Observation which
defines CB:

DEFINITIONS OF CLOUDS
Cumulonimbus: Heavy and dense cloud with
aconsiderable vertical extent, in the form of
amountain or huge tower. At least part of its
upper portion is usually smooth, or fibrous or
striated, and nearly always flattened; this part
often spreads out in the shape of an anvil or vast
plume.

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But some more insight can be obtained from the World Met Organization
code-table:
http://badc.nerc.ac.uk/data/surface/code.html (Low cloud type)

Code 3 allows a CB to be defined without the "clearly fibrous" tops, but
which must "at least partially, lack sharp outlines", ....which shows the
the icing of the tops has begun.

Code 9 CB requires the "clearly fibrous" top.

The key is that to meet the classic definition of CB, the icing of the
tops (and hence the smoother fibrous shape)... has at the very least,
begun to form.


Thanks! I have been using "CB" and "thunderstrom" interchangably, perhaps
this is not strictly true.


I agree that most observers would call a hailing cloud a CB but the hail
that fell on me yesterday was pea sized and mostly clear yet fell from a
cloud that had a top of perhaps 15,000' and was not producing thunder.


Where, geographically? And did it fall on you on the ground, or did you
encounter it in flight? And how was the cloud top determined.



North Idaho. I was on the ground (bicycling in hail of all things) The
tops I estimate at 10-12k based on my experience flying in the area (I am
confident that I could easily top them VFR). I gave 15,000' as a very
conservative estimate, I have a high degree of confidence that they were
lower. The highest terrain around is 6200' and this was sticking to the
bottom of the cloud so the vertical height was about 6000'.

Mike
MU-2