What is VIL (Vertically Integrated Liquid)?
VIL was a “fad” and was most popular when the WSR-88D radar was first installed. VIL is the integration of reflectivity within a column of air. A higher VIL means there is more precipitation in a column of air. At one time it was thought a VIL value is associated with a certain hail size. The term “VIL of the day” was a term used by the NWS to describe the VIL value that associates with severe hail (3/4″ of an inch in diameter or greater). If was found that the relationship between the VIL value and hail size is much more complex than previously thought. The VIL values correlation to hail size depends on season, synoptic environment, elevation, storm speed, storm structure, hail reflectivity characteristics etc. The relationship is too complex to issue a severe thunderstorm warning with respect to hail size from the VIL value alone, although the VIL value can be used as a guide and is especially useful if the VIL is very high.
