Complex sentence: Altocumulus often are seen preceding a cold front, especially if they take the form of altocumulus stratiformus, and the presence of altocumulus floccus or castellanus on a warm, humid, summer morning frequently signals the development of thunderstorms later in the day.
Split into simpler sentences: Altocumulus often are seen preceding a cold front, especially if they take the form of altocumulus stratiformus. The presence of altocumulus floccus or castellanus on a warm, humid, summer morning frequently signals the development of thunderstorms later in the day.