photo #7557473

If you see a sky that resembles gentle ripples on the surface of water, you’re likely looking at undulatus clouds. These can form when the airflows above and below the clouds move at different speeds or in different directions. The shearing effect in between causes the air to rise and dip as it flows. Cloud can form where the airflow rises, with gaps where it dips. When the resulting cloudy undulations stretch across enough of the sky to seem to radiate from the horizon, we refer to the pattern as undulatus radiatus. Patrick Roth (Cloud Appreciation Society Member 60,838) spotted these Altocumulus undulatus radiatus clouds lit from below at sunset over Indialantic, Florida, US, with higher patches of Cirrus appearing in shadow beyond their golden waves.