Thursday, July 21: a dry day with a nice sunset

Here’s the sunset, in case you missed it and were watching something like Entertainment Tonight and weren’t out enjoying the real world, which is so much better:

Now for some educational material.  And don’t tell me, “We don’t need no education”–who were the morons who sang that??? (Of course, you all know the answer, Led Zeppelin).  Whoever they were, they didn’t exactly change the world via new knowledge, did they?  Still, it wasn’t a bad tune.  I kind of liked it.

OK, back to clouds after that musical interlude.   You don’t see any “virga” from these Altocumulus clouds (I know I did NOT have to tell you they were Altocumulus clouds, either, did I? You already knew that by now, so forgive me).

But, you see no fall out of snow, yes that’s right, up there (in this case, about 17,000 feet above us) it would be snow dropping out of these clouds if there was some fallout from them.  Here’s the quiz:   What is the cloud top temperature of these clouds?  No help from the audience, please.

“Warmer than -10 C (14 F), and maybe even -15 C (5 F)?”  Congratulations.  You have won a trip to this web site; you will not be banned as some kind of cloud miscreant.

Yes, its true.  Even though clouds can be well below freezing, nature makes it hard to produce ice at times.  Typically, in mid-level clouds like these, the fall of snow out of them does not occur until they are at least as cold as -10 C (14 F), and every so often they can be as cold as -30 C (-22 F) with no ice.  Ice formation remains a bit of an enigma in our field.

On the other hand, clouds with warm bases, like the ones we have here on our most moist days (when they are about 10 C (50 F), can form ice between -5 and -10 C.  Its all about the sizes of the drops that accompany the cloud as it rises up into the freezing level; the bigger they are the higher is the temperature at which ice forms.  And with warmer cloud bases, the drops are bigger when they arrive at the freezing level in the tops of Cumulus clouds.

The End.