Accretion (meteorology) Accretion (meteorology) Accretion is defined as the gradual collection of something over time. In meteorology or atmospheric science it is the process of accumulation of frozen water as precipitation over time as it descends through the atmosphere, in particular when an ice crystal or snowflake hits a supercooled liquid droplet, which then freeze together, increasing the size of the water particle. The collection of these particles eventually forms snow or hail in clouds and depending on lower atmosphere temperatures may become rain, sleet, or graupel. Accretion is the basis for cloud formation and can also be seen as water accumulates
Hail spike Hail spike A hail spike or three body scatter spike (TBSS) is an artifact on a weather radar display indicative of large hail. They are identified by a spike of weak reflectivity echoes that extend out from a thunderstorm, and away from the radar site. Generally known as hail spikes, these are the result of energy from the radar hitting hail, or very heavy rain, and being reflected to the ground, where they reflect back to the hail and then to the radar as in the image on the left. This results in the radar picking up the energy from