Hail is precipitation in the form of balls or irregular pieces of ice. Hail originates in convective clouds such as cumulonimbus. Hail comes in different shapes and sizes, and is classified on the basis of size. Hail has a diameter of 5 millimeter or more; smaller bits of ice are classified as ice pellets, snow pellets, or graupel. Individual lumps are called hailstones. It is reported as "GR" in an observation and on the METAR. Small hail and/or snow pellets is reported as "GS" in an observation and on the METAR.
Severe weather detection with the NEXRAD is slightly different in the warm, moist, unstable air masses of the southeast region than it is in a region where the freezing level is generally lower. This makes the hail indicators on the NEXRAD fairly useless in the local region.
On days when the tropopause is high, thunderstorms may rise to heights well above 40,000’ without penetrating the tropopause and without producing severe weather at the surface. A median penetration of 5,000 feet occurs in storms releasing large hail.