Stratiform precipitation area
From Glossary of Meteorology
stratiform precipitation area
A region of precipitation from a nimbostratus cloud, which may or may not be an outgrowth of a cumulonimbus cloud, in which the air motions are strong enough for vapor to be condensed or deposited on particles but weak enough that the particles cannot grow effectively by collection of cloud water droplets.
Generally the vertical motions are weak enough that the growing particles fall relative to the ground. In especially well-developed stratiform precipitation, precipitating ice particles falling and growing by vapor deposition aggregate to form large snowflakes; then the snowflakes melt and produce a bright band on radar.