Cu compared with As/Ns

(Section 2.3.9.6.2)

When an extensive precipitating Cumulus is directly above, it can be confused with Altostratus or Nimbostratus or perhaps Stratocumulus stratiformis opacus (thick layer). If the precipitation is in the form of showers, the cloud is Cumulus. A continuous watch will also assist because Altostratus, Nimbostratus and Stratocumulus stratiformis opacus are noted for their longevity, which is a feature not characteristic of Cumulus.