Warmcloud

Warmcloud is a meteorological term used to describe a class of clouds in which the ambient temperatures within the cloud and its immediate environment remain above freezing, allowing the cloud to consist predominantly of liquid water droplets. In warmclouds, precipitation forms mainly through collision-coalescence, a process where small droplets collide and merge to form larger drops that eventually fall as rain or drizzle. This contrasts with cold or mixed-phase clouds, where ice crystals and phases of sublimation and freezing significantly influence precipitation.

Formation and microphysics

Warmclouds develop when moist air rises and cools but does not reach temperatures at or below 0 C through the cloud layer. High liquid water content and sufficient vertical development enable droplets to grow by collisions and coalescence. Aerosol properties, humidity, updraft strength, and cloud depth affect droplet concentration and size distribution, influencing the efficiency of rainfall formation. Because ice processes are minimal or absent, warmclouds exhibit relatively simple microphysics compared with mixed-phase clouds.

Occurrence and significance

Warmclouds are common in tropical and sub-tropical regions, as well as during warm-season convection in mid-latitudes. They often produce shallow rain events or afternoon showers and can contribute to regional weather variability and hydrology. In climate modeling and weather prediction, warm-rain processes are represented by parameterizations that describe droplet growth and rain formation without invoking ice-phase microphysics, which is computationally simpler but requires careful calibration against observations.

Relation to other cloud types

Warmclouds refer to clouds where warm-rain processes dominate. When temperatures drop below freezing within the cloud, ice-phase processes become more important, and the cloud is no longer classified as a warmcloud.