EAPS 10200 Lecture Notes - Lecture 7: Supercooling, Vertical Draft, Cumulonimbus Cloud
1 Nov 2017
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Document Summary
Hail is precipitation in the form or irregular lumps of ice. Hail only forms in large cumulonimbus clouds. Hail stones begin as small ice crystals that are circulated around a tall cumulonimbus cloud. If wind currents carry them below the freezing line they partially melt but then may circulate above the freezing line. Each trip above the freezing line results in a new layer of ice formed from the super cooled water. Eventually a strong downdraft will carry the hail to the surface. Sleet refers to small particles of ice that often resemble frozen raindrops. For sleet to form a warn air layer must lie above a freezing air layer near the surface. Raindrops leave the warm air as a liquid but pass through the freezing air. As the water raindrops pass through the freezing air they freeze often in the same form they had as raindrops. Freezing rain, also called glaze, is similar to sleet.
