Nexrad Abnormalities - Garmin AERA 660 Pilot's Manual

Hazard Avoidance
Composite data from all the NEXRAD radar sites in the United States is shown. This
data is composed of the maximum reflectivity from the individual radar sweeps. The
display of the information is color-coded to indicate the weather severity level.
The display of radar coverage is always active when NEXRAD is selected. Areas
where NEXRAD radar coverage is not currently available or is not being collected are
indicated in grayish-purple on the NEXRAD weather page. Radar capability exists in
these areas, but it is not active or is off-line.

NEXRAD Abnormalities

There are possible abnormalities regarding displayed NEXRAD images. Some, but
not all, of those include:
• Ground clutter
• Strobes and spurious radar data
• Sun strobes, when the radar antenna points directly at the sun
• Military aircraft deploy metallic dust (chaff) which can cause alterations in radar
scans
• Interference from buildings or mountains, which may cause shadows
• Poor reception from Ground Based Transceivers (GBTs) can cause portions of the
received radar imagery to not be displayed
NEXRAD Limitations
Certain limitations exist regarding the NEXRAD radar displays. Some, but not all, are
listed for the user's awareness:
• NEXRAD base reflectivity does not provide sufficient information to determine
cloud layers or precipitation characteristics (hail vs. rain). For example, it is not
possible to distinguish between wet snow, wet 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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Garmin aera 660 Pilot's Guide 190-02017-20 Rev. A