Thermal Lift Dynamics

I've been flying my 12m Silent-IN all by mysel up in Northern Maine.
I'm finding conditions are usually marginal. 5kts is the best I've
ever seen on the very best day. Typically I see 2-3kts and real
scratchy at that.

I often run into a kind of lift (particullarly up near the cloud decks)
where the lifts comes on gradually, then crashendo's and crashes behind
it. It doesn't feel like a typical thermal. It feels more like some
kind of mechanical turbulance or a sheer wall.

In other regions I've flown (Eastern Washington State) lift blew the
caps off vario and it wanted to shooved you right through bottom of the
cloud. Here (Northern Maine) it's just so weak I can barely make it to
the decks, then this "sheer lift" forms and I can't stay in lift long
enough to make good progress.

A plausable technical description of what I've observed would really
help me visualize the phenom and maybe fly it better.

Thanks,

Bruce Meacham