When thunderstorm season begins this year, pilots will start hearing some very important
changes in the way Air Traffic Control (ATC) describes radar weather echoes to pilots.
Beginning in late spring 2006, pilots will hear ATC use four terms:
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"Light"
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"Moderate"
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"Heavy," and
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"Extreme"
to describe weather radar echoes. Each term represents a precipitation intensity level
paired with a dBZ range to help pilots interpret the severity of the flight conditions
present. (A dBZ is a measure of radar reflectivity in the form of a logarithmic power
ratio (in decibels or dB) with respect to radar reflectivity factor "Z.")
The four terms will be used universally in the National Airspace System (NAS) by
approach controllers and Air Route Traffic Control Center (ARTCC) and Automated Flight
Service Station (AFSS) specialists. The decision to standardize the terminology was easy
to make, because the ARTCC facilities and many of the terminal approach control facilities
now have digital radar display systems with processors that can better determine
the intensity (dBZ) of radar weather echoes and display that information to the controller.
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