An 800 pound sailplane flying at a steady 50 knots has all forces
balanced. Lift ~ offsets weight ... i.e. the lift vector is tilted a
bit forward to generate a thrust resultant to offset drag ... let's say
it is ~ 20 pounds.

If you fly into a sharp edged 10 knot thermal at 50 knots ... the wing
'sees' a change in the relative wind equivalent to an AOA increase of ~
11 degrees.

I don't know how much lift the wing would develop ... but lets say the
lift doubles .. and doubles the thrust resultant to 40 pounds. Since
the drag is 20 ... the ship would accelerate ... but 20 pounds of extra
'thrust' on an 800 pound ship would seem to take some time to
translate into velocity. If you made the lift resultant 40 pounds ...
I still don't think you would see the speed increase we all experience.
So is something else also happening ... I think the lift vector also
tilts forward as AOA increases ... so the thrust resultant might be be
much higher. Udo ... where are you when we need you? :-)

I assumed for this example we held the stick steady ... but perhaps we
always tend to push/pressure the stick in these situations to keep the
nose from rising too sharply which effectively puts the ship in dive
....

KK