Which statement best describes a frontal zone?

• A. Broad region of high pressure
• B. A cloud type
• C. Narrow area between two air masses, width varies from .5 nm to over 100 nm
• D. An area of clearing skies after rain

Answer: (C)

Frontal zones are the boundaries between air masses that have different temperatures and moisture levels. This boundary is a relatively narrow strip, though its width can vary from about 0.5 nautical miles up to more than 100 nautical miles depending on the system. Along this zone you get abrupt changes in temperature, humidity, and often wind direction, which is why it’s a distinct feature pilots watch for weather and flight planning. The other options describe a broad high-pressure area, a type of cloud, or clearing skies after rain—none of which define the boundary between unlike air masses.