Excerpts from Jim Conrad's
Naturalist Newsletter

ALTOCUMULUS TRANSLUCIDUS CLOUDS

from the January 15, 2012 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins; limestone bedrock; elevation ~39m (~128ft), N20.675°, W88.569°; central Yucatán state, MÉXICO
ALTOCUMULUS TRANSLUCIDUS CLOUDS
Above.you see some Altocumulus translucidus clouds as they appeared over the hut early one morning this week as a warm front gushed up from the southeast.

The cotton-puff appearance cues us to the cumulus cloud type. They're not forming a distinct layer, or stratum, so they're not stratocumulus. There's too much vertical development, they're too low, and they show no wisps indicating the presence of ice crystals, so they're not cirrocumulus. What's left is "autocumulus."

The "translucidus" part of the name just means that the clouds are thin enough for light to pass through them. If they'd been so dense and packed together that light didn't pass through them or between their lumps they'd have been Altocumulus opacus. If they'd been wider apart, with light translucing through breaks between the denser lumps they'd have been Altocumulus perlucidus.

That morning the sky toward at picture's right side -- the side the warmer air was coming from -- was growing overcast. A continuous layer of mid-level cloud so thin that light transluces through it is called Altostratus translucidus.