Garmin Pilot User's Guide for iOS User Manual page 140

Fly
Composite data from radar sites in the United States is shown. This data is composed
of the maximum reflectivity from the individual radar sweeps at different title angels
of the radar beam with respect to the ground. The display of the information is color-
coded to indicate the weather severity level. Colors are used to identify the different
echo intensities (reflectivity) measured in dBZ (decibels or Z). "Reflectivity" (designated
by the letter Z) is the amount of transmitted power returned to the radar receiver. The
dBZ values increase as returned signal strength increases. Precipitation intensity is
displayed using colors corresponding to the dBZ values.
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.
• Radar base reflectivity is sampled at the minimum antenna elevation angle. An
individual radar site cannot depict high altitude storms at close ranges, and has
no information about storms directly over the site.
• Radar coverage in Canada is only available in the southern 1/4 of the country.
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Garmin Pilot for iOS User's Guide 190-01501-00 Rev. D