Based on the weather and the windshifts here yesterday, my guess would be
wind shear. Tailwind shears to a headwind and your IAS goes up. Wind shear
is also associated with bumps.

Worst I ever witnessed was when flying into a 50+ knot headwind in a C182
and it sheared to a tailwind. I saw my airspeed drop to 80, nose pitched
down, and the ground speed jumped. It sheared back to a headwind,
everything reversed, and we reset the hourglass. I remember watching cars
pass us on the interstate below.

Jim