Strengths

Like all MRMS products, the use of multiple radars is more robust than single-site radar alone. It provides faster updates and helps the forecaster integrate data from multiple radars. It also compensates for cone-of-silence, beam broadening at far ranges, and terrain blockage.

Limitations

As with single-radar VIL products, the equation used for the multiple-radar VIL product removes contamination by ice, yet it is still widely used as a predictor for hail. A popular practice is for forecasters to use a “VIL-of-the-Day” threshold for hail warning decisions. Typically, the first few hail reports are correlated with the VIL of the storm and the threshold is adjusted accordingly. It is usually observed that VILs-of-the-Day are typically lower (higher) in colder (warmer) air masses. Amburn and Wolf (1997) point out the limitations of using this practice, especially due to the varying strengths and depths of storms observed during the same time within a radar domain. Better severe warning products, techniques, and methods are now recommended.

As with single-radar VIL products, VIL is underestimated for fast-moving and/or highly-tilted storms.

Quality Control

This product is derived from the 3D Reflectivity Cube, which means non-hydrometeorological data has been removed including: Ground clutter, anomalous propagation (AP), chaff, interference spikes, and bioscatterers (e.g., angels and ghosts). However, bright band contamination remains.

Applications

Can be used to triage (quickly rank) storms based on their severe potential.

Sometimes still used to assess storms for their severe potential, particularly in a pulse severe environment.

Example Images

Fig. 1: Vertically Integrated Liquid (VIL) for a short-lived severe thunderstorm (within white circle) over
North Dakota on 21 July 2014 at 2110Z. SPC storm reports indicate 1.75-in hail was reported near the
location of the cursor at approximately this time.