vertically integrated liquid

(Abbreviated VIL.) Vertical integral of liquid water content obtained from radar observations at different elevation angles within a precipitation echo; has dimensions of mass per unit area. Liquid water content M is computed from the equivalent reflectivity factor Z_e using the Marshall–Palmer drop-size distribution and is expressed as

where the units of M are grams per cubic meter and Z_e has its conventional units (mm⁶ m^-3). The presence of hail in a storm produces larger VIL values than otherwise would be expected. VIL values greater than a threshold value are used to indicate the presence of large hail or other types of severe weather. The threshold value varies geographically, seasonally, and daily with changing environmental conditions.