Formation of rounded altocumulus clouds due to convection aloft in an unstable airmass triggered by an approaching cold front over the Islands. Notice the grey shading in the cloud parts facing the sun away which differentiates it from cirrocumulus clouds that present no shading. The first thumbnail depicts a panorama of the mid-level and another view of mackarel sky heralding the arrival of this front while the rest of the thumbnails present the weather sounding showing instability, strong winds at all atmospheric levels and wind shear, the surface pressure chart showing the cold front and the visible satellite image showing the band of clouds at the edge of the contrasting air-masses respectively.