Sailplane pilot reported temporary loss of aircraft control due to encounter with turbulence and updrafts.

Narrative

I flew an ASK-21 sailpane out of ZZZ1. The sail plane is owned by a soaring association of which I am an active member. The sail plane flight departed ZZZ1 via aero tow. The aero tow was to 3500 FT MSL. I released from the aero tow over Location A at 3500 FT MSL. The lift at the time of release was marginal at best. My initial altitude loss took me down 1700 FT MSL near ZZZ1 airfield; at which time I was able to catch a good thermal that enabled me to climb to 3700 FT MSL. As I was climbing in this thermal; the winds aloft blew me toward a north easterly direction; as the wind direction aloft was from the south west at about 230 degrees. At this stage of the flight; I found that I was underneath the ZZZ Class B shelf; which begins at X000 FT and goes up to Y000 FT MSL. Realizing I was under the ZZZ class B shelf at 3700 FT MSL; the air at this stage of the flight became very turbulent with strong updrafts. I turned to a heading of south west to fly out from underneath the ZZZ Class B shelf. I pushed forward on the control stick so as not to gain additional altitude; but the rising air current lifted the sail plane to a maximum altitude of 3800 FT MSL per the indication on the sail plane's altimeter. I deployed the wing spoilers to reduce altitude so as not to penetrate ZZZ Class B shelf.