10 Very Rare Cloud Formations

puddingtea:

1. Nacreous Clouds

2. Mammatus Clouds

3. Altocumulus Castelanus

4. Noctilucent Clouds

5. Mushroom Clouds

6. Cirrus Kelvin-Helmholtz

7. Lenticular Clouds

8. Roll Clouds

9. Shelf Clouds

10. Stratocumulus Clouds

I remember Stratocumulus Clouds once while I was in Elementary school.  These perfect rows of white with blue sky between, like a sheet of school loose leaf paper. I still think about that sky sometimes.

(Source: collthings.co.uk)