6:05 AM. Pretty ripples in Cirrocumulus below some Cirrus. What a fantastic and subtle scene this herring bone pattern was!9:34 AM. Pretty much a whole Cirrocumulus morning, punctuated by a few Cirrus clouds. Why isn’t it Altocumulus? Granulation is too tiny; no shading. BTW, no ice evident though this layer was colder than -20 C (-4 F).10:30 AM. An aircraft has punched this very thin Cirrocumulus layer and left a tell-tale ice trail that looks like natural Cirrus. Same cause for that second, white ice patch farther to the west. Its almost impossible to detect something like this since the ice trail from the aircraft is almost exactly in the form of a Cirrus uncinus. The absence of natural Cirrus is a clue about what happened.10:34 AM. The aircraft-induced Cirrus is passing overhead, and if you look VERY closely you can see that tiny “supercooled” cloudlets of Cirrocumulus are still there around it. The ice crystals fell below the Cc layer and disappeared over the next 15 minutes.2:27 PM. Later that day….widespread natural Cirrus overspread the sky, with a very thin patch of Altocumulus on the right (granulation is a bit to large for Cc).3:44 PM. Those Cirrus clouds thickened and lowered some, trending (as we would say today) toward Altostratus (translucidus–the thin version).
Today’s clouds
Today our passing cold-core trough is overhead and in the middle of it, the moisture is low enough to trigger Cumulus and small Cumulonimbus clouds as the middle and high clouds exit “stage right.” Should be an interesting day since these cumuliform clouds will be so high-based (above the Lemmon summit) and cold that lots of ice will form, producing virga, and in some places, sprinkles. A hundredth or two is possible, but that’s about it. Heck, I guess there could be some lightning here in southern Arizona as well.
This will be the last interesting cloud day for awhile, as you likely know.
Below, your weather map for 5 PM AST when there should be plenty of ice action all around:
