A cloud like this would definitely belong in an astronomical diary (taken 11 October 2014 on the Universitätsbrucke in Innsbruck)
… thunder … The 5th, Mercury’s first appearance in the east in Pisces … towards the south … It rained slowly. The 12th, a halo … The river level rose … The troops of Babylonia fought against the troops of Assyria; the troops … The 13th, the river level rose a little. The 14th, a cloud bank lay to the right of the sun. Night of the 15th, overcast. Three ra[inbows], one in the west, one between north and west, and one in the north, were seen. Rain, lightning, thunder, … clouds. The 15th, one god was seen with the other. Gusty south wind, haze crossed the face of the sky. Night of the 16th, the moon was surrounded by a large halo. The 16th, the sun was surrounded by a halo. The 18th, the sun was surrounded by a … halo; the south wind blew. The 19th, Venus stood in the region of Aries, 10 fingers behind Mars; the moon was surrounded by a halo, and α Scorpii stood in it. The 20th, Mars was 1 finger to the left of the front of Aries; it came close. The moon was surrounded by a halo, Jupiter stood in it. The south wind blew. The 27th, a rainbow whose brightness was very great stretched in the east. … in Hiritu in the province of Sippar the troops of Babylonia and Assyria fou[ght with each] other, and the troops of Babylonia withdrew and were heavily defeated. … [The no]rth wind blew. The 28th, a little rain. In the afternoon, a very red rainbow stretched in the east.
Sachs and Hunger, Astronomical Diaries and Related Texts from Babylonia, Volume I (Vienna, 1988) No. -651. All lacunae marked with /…/ are gaps in the tablet; all square brackets indicate damaged signs which could be reconstructed from context.