Decoding Guide
Radar Summary Chart
Abstract:
This chart indicates significant radar echoes from the national NEXRAD radar network. Cloud tops and cell movement are also indicated.
Description:
The complete radar summary chart contains two individual plots: Radar contours
(green) and Radar summary labels (white). The radar contours chart indicates
the Digital Video Integrator Processor (DVIP) level (an indirect measure
of precipitation intensity). The radar summary labels chart indicates the
speed and direction of cell movement, tops of clouds, and the status of
the radar at each station.
Issuance:
Hourly
Data Sources:
Radar data
Depiction:
Green, shaded contours are used to depict each of the DVIP levels (1 and
2; 3 and 4; 5 and 6). Equivalent reflectivity expressed in decibels (dBz)
is defined as the concentration of uniformly distributed small water drops
which would return the amount of power received. Precipitation typically
produces a range from 0 to in excess of 60 dBz where hail/heavy rain occurs.
The table below compares VIP level to equivalent reflectivity in dBz.
| VIP Level | dBz | Precip Intensity |
|---|---|---|
| 1 | 0 | Light |
| 2 | 30 | |
| 3 | 41 | Moderate |
| 4 | 46 | |
| 5 | 60 | Heavy |
| 6 | 57 or more |
Three levels of contours are used to indicate the returned power level. The outer contour indicates power levels of 1 or 2. Subsequent contours indicate power levels of 3&4 and 5&6.
Example:
The radar summary label data is plotted in white and provides more detailed information on the character of precipitation as well as radar operational status.
Echo heights are plotted in hundreds of feet above mean sea level (MSL) as a three digit number. Heights of tops are indicated by underlining the number: 340 = Tops at 34,000 ft. Aircraft reported tops from ARTCC sites are prefaced with the letter "A": A250 = Pilot reported tops at 25,000 ft
Cell movements have the speed denoted in knots by a number at the point of the arrow. Stationary echoes have the letters "LM" (little movement) plotted nearby.
Example:
Area of light
precipitation (with some imbedded moderate precip) with cloud tops at 21,000
and 20,000 ft. Cell is moving East-Northeast at 31 knots. Note that nearby
stations are reporting NE (No Echoes).
Operational status contractions appear at the approximate location of the
station when appropriate. The following table lists the most commonly used
contractions:
| Contraction | Meaning |
|---|---|
| NE | (No Echo) Equipment performance normal. |
| NA | Observation omitted or not available reasons not listed |
| ROBEPS | Radar operating below performance standards |
| OM | Equipment inoperative or our of service for preventive maintenance |
| RHINO | Height data unavailable |
| R | Rain |
| trW | Thunderstorm |
| SLD | Solid line of returns (usually thunderstorms) |
| RW or SW | Rain or snow showers |
| NS | Equipment performance normal; non significant precipitation echoes are being reported. |