Garmin Aera 660 Pilot's Manual page 122

Hazard Avoidance
Radar Limitations
Certain limitations exist regarding the NEXRAD radar displays. Some, but not all, are
listed for the user's awareness:
cloud layers or precipitation characteristics (hail vs. rain). For example, it is not
possible to distinguish between wet snow, wet hail, and rain.
individual NEXRAD site cannot depict high altitude storms at close ranges, and
has no information about storms directly over the site.
Radar Intensity
Colors are used to identify the different NEXRAD echo intensities (reflectivity)
measured in dBZ (decibels of 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.
RADAR Legend
Radar Products
FIS-B weather provides two different Radar products, CONUS and Regional. The
system can display each individually or a composite (COMBINED). When Regional
Radar is displayed, only precipitation for the current region is displayed. The subdued
(grayish-purple colored) area represents the area not covered by the regional radar
product. When Combined radar data is viewed, Regional Radar data is displayed on
top of CONUS data and the time shown in the lower left corner is associated with
Regional Radar data only.
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Garmin aera 660 Pilot's Guide
NEXRAD Data
190-02017-20 Rev. E