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Radar Data Details

There are several types of radar data including Manually Digitized Radar (MDR), Radar Coded Messages (RCM) and NEXRAD data (NIDS). These data come from meteorological radars placed at various locations across the US. The RCM messages are combined into a national mosaic which is what is presented below. The images are updated twice an hour at :05 and :35.

Radar Coded Message Plots

These data come from NEXRAD doppler radars placed at various locations across the US. Each radar site reports a digitized assessment of the precipitation echoes displayed on the radar summary. Precipitation intensity is determined based on a scale from 1 (light) to 6 (extremely heavy). This information is recorded on a grid which covers the country and has a spacing of around 12 kilometers. This is coarse compared to the radar which can get detail of around 1 kilometer. The radar also reports echo tops, storm movement, hail probability and location of tornado vortex signatures (TVS) and mesocylones (MESO). Both TVS and MESO indicate the location of rotating areas of winds within the thunderstorm complex. TVS signatures are more concentrated and can indicate the potential for the development of a tornado.

Also, the National Weather Service provides information about severe weather watch boxes (either Severe Thunderstorm or Tornado) which can then be plotted on the radar summary. These data are updated twice an hour at 15 and 45 past the hour.

Composite Radar Summary


Sample composite radar summary
Sample composite radar summary

The composite radar summary is a plot of most of the available information broadcast as part of the RCM radar data.

Radar summary
The first plot is the actual radar summary. The radar summary displays areas where precipitation is falling. The intensity is based on color where:

Color Dbz Intensity Description
DGreen ~20 Light light rain or snow
MGreen ~30 Moderate
BGreen ~40 Heavy light thunderstorms/moderate rain showers
Yellow ~45 Very Heavy moderate thunderstorms
Orange ~50 Intense potential flooding rains/strong thunderstorms
Red >55 Extreme flooding rains/potential severe thunderstorm

Radar sites that don't report precipitation can report either:

NE - No echos/precipitation within the radar range.
NA - Radar data not available.
OM - Radar inoperative due to maintenance.

Storm movement
The next type of data is the individual storm movement which is plotted as a wind barb (See Weather Symbol Legend). This indicates how fast and in what direction the individual storms are moving.

Precipitation tops
The next type of data is the precipitation tops which are plotted over the top as a number in 100s of feet. This is the maximum altitude of the precipitation as seen by the radar. This can range from 10,000 feet in snow showers to 20,000 with rain showers to 40,000 feet with thunderstorms. Severe thunderstorm tops can reach 50,000 to 70,000 feet.

Severe weather watch boxes
The last type of data are the severe weather watch boxes. The area covered by the watch is enclosed by a white box. The watch number and type as well as the expiration time are also listed.

to 5Z
Specifies a tornado watch #335 which expires at 5Z
to 8Z
Specifies a severe thunderstorm watch #336 which expires at 8Z