Garmin Pilot Guida Utente

190-01532-00  Rev. G

52

Weather radar data is collected from radar sites across the United States, Canada, 

and select overseas locations.  It is combined into a mosaic for easier display and 
analysis. 

The radar data displayed is not real-time.  The lapsed time between collection, 

processing, and dissemination of radar images can be significant and may not reflect 
the current radar synopsis.  Due to the inherent delays and the relative age of the 
data, it should be used for long-range planning purposes only.  Never use radar data 
to penetrate hazardous weather.  Rather, use it in an early-warning capacity for pre-
departure evaluation.

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 tilt 
angles 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.

There are possible abnormalities regarding displayed radar 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