Differentiating Precipitation Returns

If your aircraft is equipped with both SXM Weather with NEXRAD and airborne weather radar, and your system provides for multiple panes, it is possible to display two separate panes to monitor for precipitation. While NEXRAD returns will not show the current location or state of a thunderstorm cell, it can show that precipitation is present in the area, and help you to differentiate precipitation returns from ground clutter returns.

Figure 8 shows a NEXRAD overlay on a Navigation Map pane. From this display we can tell that precipitation is present in the area and that the winds aloft are from the East. Figure 9 shows the airborne weather radar display exploring the air mass ahead of the aircraft. This display also shows lightning strikes have occurred in the area, and it shows a strong radar return over EYW (the Key West area). The NEXRAD display (Fig. 8) only shows small cells beyond EYW, which makes it likely that the return at EYW is actually ground clutter produced by the islands located there. The fact that there is no radar shadow cast beyond the islands makes this even more likely.

See Vertical Scan Mode for a description of how the Vertical Scan mode feature is used to aid in differentiating land features from precipitation.

KEY POINT: NEXRAD displays do not provide real-time weather  images.  This must be kept in mind when comparing with airborne weather radar returns.

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