Garmin GXM 40 - Manual (Page 36)

4 GXM 40 Owner’s Manual
Appendix
NEXRAD Overview
NEXRAD Description
NEXRAD Radar is a Doppler radar system that has greatly
improved the detection of meteorological events such as
thunderstorms, tornadoes, and hurricanes. An extensive
network of NEXRAD stations provides almost complete
radar coverage of the continental United States, Alaska,
and Hawaii, and the majority of Canada. The range of each
NEXRAD is 124 nautical miles.
NEXRAD Abnormalities
There are possible abnormalities regarding displayed
NEXRAD images. Some, but not all, of those include the
following circumstances:
Ground clutter
Strobes and spurious radar data
Sun strobes, when the radar antenna points directly at the
sun
Military aircraft deployment of metallic dust (chaff),
which can cause alterations in radar scans
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Interference from buildings or mountains, which may
cause shadows
NEXRAD Limitations
Certain limitations exist regarding the NEXRAD radar
displays. Some, but not all, are listed here for your
awareness:
NEXRAD base reflectivity does not provide sufficient
information to determine cloud layers or precipitation
characteristics (for example, determining between hail
and rain).
NEXRAD base reflectivity is sampled at the minimum
antenna elevation angle. An individual NEXRAD site
cannot depict high altitude storms at close ranges, and
has no information about storms directly over the site.
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