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EFAS. Assuming that you do find or suspect deteriorating conditions while en route, be sure to contact the En route Flight Advisory Service (EFAS – Flight Watch) for additional information. EFAS can be an immensely helpful resource, but interpreting and applying the information you receive while you are also flying the aircraft – especially if you are in adverse or deteriorating conditions with no autopilot – can be very challenging.  The key is understanding where the weather is in relation to your position and flight path, where it is going, and how fast it is moving. A good practice is to have an aeronautical chart with your route clearly marked readily available before you call Flight Watch.  The chart will help you visualize where the weather conditions are in relation to your current position and intended route of flight, and determine whether (and where) you need to deviate from the original plan.  
Another interpretation useful tool is the In-flight Advisory Plotting Chart (figure 7-1-2 in Chapter 7 of the Aeronautical Information Manual (AIM)).  This chart includes the location and identifier for VORs and other locations used to describe hazardous weather areas. Consider keeping copies of this chart in your flight bag for easy reference whenever you call EFAS.
ATC. ATC radar can detect areas of precipitation, but does not detect clouds or turbulence.  The existence of turbulence may be implied by the intensity of a precipitation return: the stronger the return, the more likely the presence of turbulence.  Similarly, icing may be inferred by the presence of moisture, clouds, and precipitation at temperatures at or below freezing.

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.  Consequently, approach controllers, center controllers, and AFSS specialists have all begun using four terms to describe weather radar echoes to pilots:  “light,” “moderate,” “heavy,” and “extreme.”  Each term represents a precipitation intensity level paired with a decibel (dBZ) range to help pilots interpret the severity of the flight conditions present. (Note: A dBZ is a measure of radar reflectivity in the form of a logarithmic power ratio with respect to radar reflectivity factor “Z.”)
Although the terms are consistent, there are still some equipment-related differences in what can be described.
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In Air Route Traffic Control Centers, NEXRAD data is fed through the Weather and Radar Processor (WARP), which organizes 16 NEXRAD levels into four reflectivity (dBZ) categories. Reflectivity returns of less than 30 dBZ are classified as “LIGHT” and are filtered out of the center controllers’ display, which means that center controllers cannot report areas of “light” weather radar echoes.
　
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本文鏈接地址：General Aviation Pilot’s Guide to Preflight Weather Planning, Weather Self-Briefings, and Weather Decision Making(14)