A nationwide weather radar network is used to detect precipitation throughout the country.
A radar weather report, referred to as an SD, is a textual description of radar returns, issued at 35 minutes past each hour with special reports issued when necessary.
A graphic depiction of radar should provide more detail, but textual radar reports provide this information to pilots who do not have access to a graphical radar summary.
Here is an example of a radar weather report:
Example: TLX 1935 LN 8TRW++ 86/40 164/60 20W MTS 570 159/65 C2425 AUTO ^MO1 NO1 ON3 PM34 QM3 RL2
Radar Site Identifier
The first item is the three letter identifier of the radar site generating the report.
In this case, the report was generated by the radar in Norman, Oklahoma.
Next is the Zulu time of the report.
This example report reflects weather that existed at 1935 Zulu time.
Radar Return Configuration
Following the time, the configuration of the radar returns will be stated.
In this example, the weather is a line.
A line describes weather which is 30 or more miles long, and is at least four times long as it is wide, with radar returns covering at least 25% of the area within the line.
Weather may also be described as being a cell, which is a single echo by itself, or an area when a group of radar returns exist, but to not form a line.
Precipitation Coverage, Type, and Intensity
Next, the coverage in tenths, precipitation type, and intensity are described.
In this example, the coverage is 8/10, or 80%.
The precipitation type is coded as one of five types:
- rain (R)
- rain shower (RW)
- snow (S)
- snow shower (SW)
- thunderstorm (T)
Precipitation intensity is indicated by a minus symbol for light intensity, a plus or plus plus symbol for heavy intensities, and an X or XX for extreme intensities.
The example report indicated 8/10’s coverage of thunderstorms and heavy rain showers.
Location information is now added, in the form of azimuths and distances from the radar site.
In this case the line of rain showers extends from a point 86 degrees and 40 miles from the TLX radar sight, or roughly 40 miles east of Norman to a point 164
degrees and 60 miles from the TLX radar site, which is 20 miles in width.
An area of weather will also be described as two points and a width.
A weather cell, however, will be coded as an azimuth and distance, with the diameter of the cell.
For example, this code (“135/102 D10”) describes a cell 135 degrees and 102 miles from the radar site, which is 10 miles in diameter.
Maximum Precipitation Tops
Following the width or diameter, the maximum tops are given by the letters “MT” and the maximum tops in hundreds of feet, followed by the azimuth and distance of the maximum tops.
The example shows maximum tops at 57,000 feet located 159 degrees and 65 miles from the Norman radar site.
“MTS” in place of “MT” indicates satellite data was used together with radar data in making the maximum tops determination.
“MT” alone indicates radar data was the sole source of the maximum tops data.
The next item in the report describes movement of the radar returns.
The letter “C” signifies the cell movement portion of the radar weather report.
It is followed by two numbers which represent the direction from which the weather is moving and two more digits representing the speed of the movement.
The example report shows the weather to be moving from 240 degrees, from the west to the east, at 25 knots.
Next one of four remarks are added to the report.
- “AUTO” indicates the report was automatically generated by the weather radar system.
- “PPINE” means no echoes were observed by this radar site.
- “PPINA” means data from the radar site is not available.
- “PPIOM” means the radar site is down for maintenance.
The final part of a weather radar report is the digital section, which is generated by the radar site to be used, not by pilots, but for the generation of the radar summary chart.