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Refer to the FAA Approved Airplane Flight Manual and to the FAA Advisory Circulars referenced on page 3 for detailed information on flying in the vicinity of and avoiding thunderstorms and turbulence. 
The most intense echoes indicate severe thunderstorms.  Remember that hail may fall several miles from the cloud, and hazardous turbulence may extend as much as 20 miles from the cloud.  You should avoid the most intense echoes by at least 20 miles, if possible. 
As echoes diminish in intensity, you can reduce the distance by which you avoid them. 
PATH PLANNING CONSIDERATIONS 
. You should avoid all cells containing magenta and red areas by at least 20 nm, if possible. 

. You should not deviate downwind unless absolutely necessary.  Your chances of encountering severe turbulence and damaging hail are greatly reduced by selecting the upwind side of a storm. 

. Only use the turbulence indication to isolate turbulence from precipitation.  You should avoid all areas displayed as red or magenta. 

. An area of displayed turbulence not within 20 nm of a red cell area should be cleared by 5 nm, if possible. 

. A “Blind Alley” or “Box Canyon” situation can be very dangerous.  When viewing the short ranges, periodically switch to longer-range displays to observe distant conditions.  In the example shown to the right, the short-range returns show an obvious corridor between two areas of heavy rainfall but the long-range setting shows a larger area of heavy rainfall.

. Thunderstorms build and dissipate rapidly.  Therefore, you SHOULD NOT attempt to pre-plan a flight plan course between closely spaced echoes, or under or over convective cells.  Avoid individual storms in flight either by visual sighting or by use of airborne radar. 

 

AZIMUTH RESOLUTION 
Azimuth resolution is a function of the beam width.  When two targets are closely adjacent in azimuth and at the same range, the radar may display them as a single target.  However, as the targets are approached they appear to separate.  The ability of the radar system to resolve these targets is a function of the antenna’s beam width and the range of the target. 

SHADOWED AREAS 
Extremely heavy rainfall or high terrain can reduce the ability of the radar to penetrate and present a full picture of the weather area.  This is referred to as “radar attenuation”.  Using MAP mode in combination with the weather modes allows areas of shadowing to be easily identified.  Observe the ground returns in the area behind the strong weather echo.  With very heavy intervening rain, the ground returns behind the echo will not be present but rather will appear as a shadow.  This may indicate a larger area of precipitation than appears on the weather display. 
EFFECTS OF INTERFERING RF SOURCES 
An interfering radio frequency (RF) source operating at a frequency close to the radar’s operating frequency can create unusual returns on the display.  Most of these returns are suppressed by algorithms in the software.  However, when being subjected to external RF interference, a few scattered weather or turbulence spots will get into the memory.  These spots will typically be removed after the antenna re-scans the area and updates the memory; approximately thirty seconds.  These returns are caused by Continuous Wave (CW) sources of RF radiation.
CW RF sources that can cause this effect include: 
. CW Military Radar 

. Radar Jamming Equipment 

. Satellite Uplink Equipment 

Adjusting the manual gain may help alleviate the effect of the interfering source but the effect will not completely disappear until the interfering source is no longer in the radar’s field of view and that area of the memory has been refreshed. 
　
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