why are some clouds black while others are white

November 5, 2009 9:14 AM

Why are some clouds black while others are white?

So looking out of my window I can see storm clouds coming in and they are black (well dark grey) even the wispy bits at the top of them while other clouds higher up are white.

Do the dark clouds look that way because of water content?

posted by zeoslap to Science & Nature (4 answers total)

Best answer: They look that way because of how they're lit. More info.
posted by jquinby at 9:16 AM on November 5, 2009

Response by poster: Had I waited a while I'd have seen those very same clouds turning white as the sun came out a bit more :)
posted by zeoslap at 9:28 AM on November 5, 2009

Best answer: You're seeing shadowing underneath the base of the cloud. All parts of a cloud reflect white and have a very high albedo (reflectivity) if they're sufficiently illuminated, though depending on the phase (ice or water) and particle type this can be slightly lower or higher. Any part of any cloud will be bright white if illuminated by direct sunlight, unless it's been infiltrated by a duststorm or some other particulate matter.
posted by crapmatic at 9:31 AM on November 5, 2009 [3 favorites]

The main thing is that storm clouds (cumulonimbus) are very tall, which means there's a lot more cloud filtering out the sunlight.
posted by Sys Rq at 10:48 AM on November 5, 2009 [1 favorite]