Paul kgyy wrote:
Assuming that the turbulence consists of a series of up- and
down-drafts, each bump creates a change in the angle of attack, which
would change the airspeed reading. However, I'd expect it to go both
up and down, not just up unless the bumps were generally in the same
direction. They could be unidirectional if you were flying just above
or below a boundary layer, which often occurs in the midwest.

Is a 'bump' an updraft, or is it an increase in headwind? The headwind
would make the plane go up and also appear faster, while a drop in wind
makes it lower and slower. The plane may be stable in such a way that
the drops cause the nose to go down and recover speed, but the lifts
do not (as much) cause the nose to rise. The net result would be more
airspeed.

John Halpenny