Cirrus posts bring together some of the Cloud links and resources I find from a range of feeds and shared contacts.
I noticed in Wikipedia that:
The random, isolated cirrus cloud does not have any particular significance. A cirrus castellanus cloud indicates that there is instability at the cirrus level. However, a large number of cirrus clouds may be a sign of an approaching frontal system or upper air disturbance. This usually signals a change in weather in the near future, usually becoming increasingly stormy.