Frequently Asked Questions about the Storm Information Table with Storm Timer(tm)

Answers

What Is The Storm Attributes Table With StormTimer(tm)?

The NEXRAD Doppler radar Storm Attributes Table shows information about the severity of specifically identified storms. The information in the table is generated solely by the NEXRAD radar. The NEXRAD radar also identifies and tracks individual thunderstorms. The StormTimer projects the movement of the storm. If the NEXRAD data analysis process has found no storms, the message "No Storms Detected" will appear in place of the Storm Information Table.

How Does The Storm Timer Tell Storm Movement?

The Storm Timer product predicts the movement of storms based on their current velocity (direction and speed). The arrow points in the current direction with each square at a set time (0, 15, 30, 45 minutes ahead) and the arrowhead representing the storm's destination in 60 minutes.

What Do Each Of The Storm Table Columns Mean (TVS, MESO,etc.)?

The colums in the Storm Information Table are explained as follows.

ID# (Identification Number)  - The storm ID identifies individual storms that have been designated as such by the NEXRAD radar. Each Radar site assigns their own storm ID even though the same storm may be seen by two or more radars. The storm ID appears on the Storm Timer layer as a two letter code. Although there may be more ID's in the Storm Information Table, only the first 8 are marked on the Storm Timer layer because of clutter problems.

AZM (Azimuth) - The direction, in degrees from the radar site, in which the storm is located. Not to be confused with DIR (Direction) which is the direction from which the storm is moving.

RNG (Range) - The distance from the radar site to the identified sto rmin miles.

TVS (Tornadic Vortex Signature) - TVS or ETVS (Elevated Tornadic Vortex Signature) is a signature of a potential tornado indicated by the NEXRAD radar. NEXRAD will indicate "TVS" or "ETVS" if the rotational shear that has been calculated by the NEXRAD radar is judged strong enough that the storm may produce a tornado or "NONE" meaning no tornado vortex signature is detected (there is either no rotation or the rotational shear is not of sufficient strength to result in a tornado) as judged by the NEXRAD radar. The National Weather Service will issue tornado warnings based on the strength of the TVS or ETVS signature.

MESO (Mesocyclone) - MESO (Mesocylone identified), UNCO (Uncorrelated Shear (2-D) identified), or 3DCO (3-D Correlated Shear identified) will be present if the NEXRAD radar indicates rotation on a slightly larger scale then the TVS signature within a thunderstorm. (NOTE: During the summer of 2007, the NWS is gradually switching radars from the MESO/3DCO/UNCO scale to a numerical scale, where low numbers represent weak rotation, and numbers above 5 are considered "strong" by the National Weather Service. They also add "L" to the number when the circulation is low-level (near the ground).. Mesocyclones are the parent rotation for tornado development. Seen at the surface, a mesocyclone is the wall cloud in the southwest part of a supercell thunderstorm. NEXRAD will indicate "MESO", "3DCO" or "UNCO" if rotation has been detected or "NONE" if no rotation is detected.

PSH (Probability of Severe Hail) - This is the probability that the identified storm contains Hail that meets the National Weather Service's criteria for a "Severe Thunderstorm", which is a diameter of 3/4" or larger.

POH (Probability of Hail) - Stands for the probability of hail within a thunderstorm based on measurements from the NEXRAD radar. The probability of hail is used in conjunction with the probability of severe hail to provide information on the potential for hail damage.

MXSZ (Maximum Predicted Size Of Hail) - This is calcuated by the radar to provide a prediction of the maximum size of hail occurring in the identified storm at the time of observations.

VIL (Vertically Integrated Liquid) - Vertically Integrated Liquid (VIL) shows the amount of liquid water contained in a vertical column over each point on the display. The data is measured in kilograms per square meter, a measure of volume. The computer programs that create the Vertically Integrated Liquid (VIL) product use as their input the reflectivity data gathered from all the elevation angles surveyed during the volume scan (as is displayed in the four tilts of the Base Reflectivity product and the Composite Reflectivity product). The computer programs assume that all reflectivities are from liquid water and then use equations to convert the reflectivities to liquid water content. Hail has unusually high reflectivities (much higher than the largest raindrops) which can cause this product to overestimate the amount of liquid water actually contained in the clouds. For this reason, very high VIL values in thunderstorms are a good indication that hail may be occurring. VIL data is useful in distinguishing thunderstorms from rain showers. The thunderstorms will tend to have relatively higher VIL values, although the threshold VIL value for the difference between a rain shower and a thunderstorm will differ from one location to another, due to differences in atmospheric conditions and climate. Also, as thunderstorm development progresses, relative VIL values can help differentiate between strong thunderstorms that may be severe and thunderstorms that are not likely to be severe. However, VIL data must be used in conjunction with the other NEXRAD products and weather data other than radar data to determine the likelihood that a particular thunderstorm may produce severe weather. Furthermore, the relationship of VIL to the occurrence of severe weather is different and needs to be defined separately for different atmospheric conditions and climate regimes. The correlation that can be made using VIL data is that the precipitation areas with the highest VIL data levels are the strongest echoes within the radar's coverage area. For a line of thunderstorms (a squall line) examination of the VIL values can help determine which storms in the squall line are the strongest and have the highest potential for producing severe weather.

DBZ (Maximum dBZ Level) - This is defined as the maximum dBZ reading with in a storm as detected by NEXRAD radar. For more information on dBZ see here.

HGT (Maximum dBZ LevelHeight) - Height of the maximum dBZ or reflectivity, in thousands of feet. For example, 14.6 means the highest reflectivity level detected in the storm is at an altitude of 14,600 feet.

TOP (Storm Top) - Indicates the height of the top of the storm in thousands of feet above the radar's antenna. The NEXRAD computer typically gives the height of the top of the 30 dBz reflectivity which may not always correspond with the top of the storm's cloud. For example, an entry in the TOP column of 14.8 indicates the top of the 30 dBz reflectivity in the storm is at an altitude of 14,800 feet above the radar.

DIR (Direction) - The direction (in degrees) FROM which the identified storm was determined (by the radar) to be moving. Subtract 180 degrees to get the direction in which the storm is moving TO. Or, even better, just check the StormTimer, which shows arrows based on this direction information.

SPD (Speed) - The speed at which the identified storm was determined (by the radar) to be moving, in knots. This information is used to create the AccuWeather StormTimer.