Puzzle - Hay gained moisture in Barn?

This may sound like a dumb question, but will hay bales (std square) gain moisture in storage. When cutting I had 10 to 12% moisture or lower at the baler and in the bales on the ground. Twist test and hay moisture meter said all was good at that time. That was less 4 days ago. Now I am reading 14 to 22% in the stack. Did I do something wrong, or is this normal?

 

Concerned

Thanks - Keith

 

PS This is normal mixed grass hay with a bit of clover. Cut with a drum mower and tedded twice - 5 days dry down before baleing.

Puzzle - Hay gained moisture in Barn?