Pentrating Towering Cumulus Clouds

"Icebound" wrote in message
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"Mike Rapoport" wrote in message
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"Ron McKinnon" wrote in message
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"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.


Do you have a source of this definition? I can't find one but while
looking, I found several sites with pictures of CBs that don't all have the
wispy tops

Here is one: http://www.chitambo.com/clouds/cloudshtml/calvus.html


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.



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.

Mike
MU-2