March Morning Undulations

A large bank of altocumulus undulatus clouds, illuminated by the rising sun, dominate the northeast sky as seen from Brentwood Drive NE in Cedar Rapids, Iowa just after 7:00 AM, Tuesday, March 1, 2011. The presence of this type of cloud, which occurs from a height of 6,500-16,500 feet, may herald the imminent arrival of an approaching front, and indeed light rain and drizzle arrived on Thursday night. Altocumulus indulatus is caused by a lifting of a large air mass followed by condensation combined with instability and wind shear at cloud level (the reason for the striking "undulating" patterns). Air temperature at this moment was around 25 degrees F.