When a NEXRAD radar make a volume scan, the data is examined using a special algorithm which tries to identify storm cells. For each identified cell, a number of characteristics or "attributes" are either measured from the radar data or derived from other algorithms. Attributes for all identified storm cells are tabulated to form the "storm attributes table". WeatherTAP provides a means for the user to examine this data both graphically and in text form by use of the RadarLab feature. A sample storm attribute window is portrayed below:

Each attribute will be discussed in detail below:

DISPTRK

This value is actually not part of the storm attribute. Instead, it determines whether or not this cell is plotted as part of the RadarLab "Storm Tracks" overlay.

ID

When a storm cell is identified by the NEXRAD site, an alphanumeric identifier is assigned. This identifier is arbitrary and contains no specific information about the storm. It's simply an identifier.

AZ

This is the azimuth (in degrees) of the position of the cell relative to true North. Taken together, the AZ and RNG parameters describe the relative location of the storm cell in Polar coordinates.

RNG

This is the distance (in miles) between the radar site and the identified cell. Taken together, the AZ and RNG parameters describe the relative location of the storm cell in Polar coordinates.

TVS

This is the Tornadic Vortex Signature. If the NWS Tornado Detection Algorithm detects sufficient tornado-like rotation in the volume scan, then this value will change to either "TVS" or "ETVS" (Elevated TVS). The current TDA looks at high values of gate-to-gate shear and was developed over many years. More information on the TDA algorithm is available here.

MESO

This is the mesocyclone signature. If the NWS Mesocyclode Detction Algorithm (MDA) detected a mesocyclone-like rotation in the volume scan then this value will change to "MESO", "UNCO" (uncorrelated 2-D shear), or "3DCO" (correlated 3-D shear).

POSH

This is the percent probability of severe hail.

POH

This is the percent probability of hail.

MXSize

This is an estimate of the maximum size of hail associated with the identified cell. The estimate is produced from an algorithm and is reported in inches.

VIL

This is the VIL (Vertically Integrated Liquid Water) value associated with the cell. VIL is the amount (mass) of water which would be condensed out of a colum of air located at the centroid of the cell. The VIL quantity is reported in Kg/m^2.

DBz

This is the maximum amount of reflected radar energy present within the cell from any elevation.

HT

This is the height that the maximum DBz (see above) occurred. This height is reported in thousands of feet, i.e. 1.6 means that the maximum value of reflectivity occurred at 1,600 ft.

Tops

This is the echo tops value of the cell determined by radar. Tops are reported in thousands of feet, i.e. 23.4 means that the cell tops are at 23,400 ft.

Spd

This is the speed at which the cell is moving (not the maximum speed of the wind contained within the cell). This value is reported in knots.

Dir

This is the direction in which the cell is moving from. To get the direction that the cell is moving to, simply subtract 180 from this value. This value is reported in degrees.

Additional Information

NSSL Tornado Detection Algorithm

Detection of Mesocylcones using Doppler Radar