What are characteristics of a moist, unstable air mass?

• A. Cumuliform clouds and showery precipitation
• B. Stratiform clouds and steady rain
• C. Clear skies
• D. Very dry air

Answer: (A)

When air is moist and unstable, convection kicks in. That means rising air parcels are buoyant enough to keep climbing, rather than leveling off. The moisture in the air condenses as the parcel rises and cools, releasing latent heat, which adds to the buoyancy and makes the air parcel rise even more. This combination produces vertically developed, cumulus-type clouds, which are the telltale sign of strong vertical motion. Because the atmosphere is unstable and convection is active, the precipitation tends to be in showers rather than a uniform, steady rain, often with a lively, popping cloud field.

If the air were stable, lifting would be gentle and spread out, leading to stratiform clouds and more uniform, steady rain rather than the tall, puffy clouds and showery bursts seen with convection. Clear skies come from dry, very stable conditions where little condensation occurs, and very dry air lacks the moisture needed for cloud formation in the first place.