O. Sami Saydjari wrote:

1. Assuming that thunderstorms were not predicted for the area, is my
concern unjustified?

I once flew into a towering cumulus in a C172 and had some interesting
things happen. I was on an IFR training flight and had been solid IMC
for about a half hour when we popped out to spot the most beautiful
towering white monster dead in our path that shot straight up to about
20k. It was clear blue all around except for the TC.

I asked my CFII if this was a problem and if I should ask for other
routing. He seemed unconcerned and so we proceeded directly into it.
I didn't question him because, after all, I was a lowly IFR student( an
attitude that I have thoroughly revamped ) and he had some 5000 hours of
flying on the logs.

The first thing that happened was a strong downdraft that pegged the
VSI, followed by small hail hitting us that sounded like the airplane
was being "sandpapered". We went through some wild oscillations of yaw
and 200-300 ft altitude excursions. The yoke required full right and
left deflection at times to keep upright and the seat belts cut into us
enough at times to be noticeable.

Then, I felt a static charge all over my arms ( the hairs actually rose
up!) that seemed to build followed by most of the instruments going TU.
The only instrument that seemed stable enough to be usable was my little
hand held GPS which allowed me to keep the aircraft level by watching
the GPS compass card.

We exited as suddenly as we entered into calm blue sky. The contrast was
actually kind of eerie!

3. Wouldn't large towering cumulus clouds have chartacteristics similar to thunderstorms
(severe turbulence, possible hail, heavy rain, icing) even if they don't end up becoming an
official thunderstorm (lightning present).

Yes, would be my answer.

Antonio