"Mike Rapoport" wrote in message
ink.net...

"Ron McKinnon" wrote in message
newscD8e.1052899$8l.772250@pd7tw1no...

"Mike Rapoport" wrote in message
nk.net...

TCU have, as you would expect, characteristics between CU and CB clouds.
All three can be thought as different stages of the same think, a cloud
pruduced by convection. Obviously three seconds before a TCU starts
producing lightning and becomes a CB, it is going to a lot like a
thunderstorm inside.

A minor point: A TCU will not 'produce lightning to become a CB'. If
it produces lightning it *is* a CB, and has been for some time, but it
is
not the production of lightning that makes it a CB.


That is what I said ( I think) A thunderstorm becomes a thunderstorm when
the thunder starts. Three seconds before the first lightning, it is still
a TCU.

Well, no. A TCU becomes a cumulo-nimbus when the rounded califlower-like
shape of the TCU begins to top off with a wispy fibrous top, often
stretching downwind like an anvil. This is ice crystals forming at the very
top of the cloud.

That is the classic definition used by weather services. Observers will not
call it a CB if they continue to see the hard-edged form at the tops.... not
until they see the formation of the wispy fibrous top. However, once
lightning, or hail, or funnel-clouds are observed, the observer will almost
surely class it a CB, regardless.



It is not necessary that a CB produce lightning, nor hail, nor heavy
precipitation, nor Mammae, Funnel Clouds, Tornados or Waterspouts.
It can do none of these things and still be a CB. But if any of these
things happen it is necessarily a CB.

I am not sure what you are saying here, If it doesn't produce lightning it
isn't a thunderstorm (CB) so I would say that it is nessesary for a CB to
produce lightning.

The production of the ice-crystals at the top will normally be accompanied
by lightning, but ever if it is not, it would still be called a CB if the
fibrous ice-crystal anvil-shaped top exists.



Conversely, when a TCU is only slightly taller than a CU, it is going to
be more like a CU inside. There is a relationship between the vertical
height of a convective cloud and turbulence but it is not absolute. I
have never heard of large hail coming from anything other than a big CB.

If it hails, it's a CB, by definition. A TCU can produce snow
pellets, however (and ice pellets, I think (it's been a while)),


This is the first time that I have heard that hail defines a thunderstorm.
A thunderstorm is defined by lightning (and therefore thunder). Hail is
produced by updrafts in a cloud through the freezing level allowing frozen
precipitation to remain aloft and grow. I don't see why this couldn't
happen without lightning. I was hailed upon yesterday and there was no
thunder.


Hail (hard "real" hail, not the soft stuff in some cold-weather cumulus)
.... Hail does not define a thunderstorm, but because the conditions required
for it are typically exactly the same that produce lightning and the rest of
the CB symptoms, you will be hard pressed to find an observer who will not
call a hailing cloud a CB, just because he hasn't seen lightning or heard
thunder.