Family B: Middle Clouds 



(Mean upper level, 6,000 meters, 20,000 feet; mean lower level. 2,000 meters 



6,500 feet) 



4. Altocumulus. 



5. Altostratus. 



Family C: Low Clouds 



(Mean upper level, 2,000 meters, 6,500 feet; mean lower level, close to the surface) 



6. Stratocumulus. 



7. Stratus. 



8. Nimbostratus. 



Family D: Clouds With Vertical Development 



(Mean upper level, that of cirrus; mean lower level, 500 meters, 1,600 feet) 



9. Cumulus. 



10. Cumulonimbus. 



