Instantaneous contributions to the normal force on a thick airfoil at high Reynolds number are determined over a range of angles of attack. In order to establish the possible loss of statistical invariance in the spanwise direction, the investigation is based on two rows of pressure sensors around the airfoil, both located close to its center. Evidence of statistical asymmetry between the chords is observed for angles of attack corresponding to the onset of separation. The pressure fluctuations on both chords are characterized by a local maximum that is located directly upstream of the separation point. Abrupt temporal changes are observed in the evolution of the local maximum fluctuations and are found to be anti-correlated in the spanwise direction, which confirms the observations made by Neunaber et al. (Wind Energy 2022). POD analysis along the chord shows that these dynamics can be attributed to a dominant spatial mode that evolves continuously with the angle of attack.