What does ACC signify in a METAR report?

ACC in a METAR report signifies Altocumulus castellanus, which refers to a specific type of cloud formation. These clouds are typically found at altitudes of 6,500 to 23,000 feet and are characterized by a particular bulging or tower-like appearance that resembles a castle. The presence of ACC can be significant for meteorologists as it indicates instability at higher altitudes, which may lead to the development of convective weather patterns.

Recognizing this term is important for interpreting weather conditions, as it can inform pilots and meteorologists about potential turbulence and weather changes. The other choices do not accurately represent cloud types recognized in meteorological reports, thus reinforcing the importance of understanding specific terminology in METAR decoding.