BendixKing IN-862A System RDR-2100 - Manual (Page 24)

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Effective Date: 9/98 RDR 2100 Pilot's Guide: Rev 1
THUNDERSTORMS & TURBULENCE
The RDR 2100 can give you a clue to the presence of turbulence. Areas
of the display where the colors change rapidly over a short distance rep-
resent steep rainfall gradients, which are usually associated with severe
turbulence.
Turbulence may be divided into two basic types: (1) clear-air turbulence;
and (2) turbulence associated with thunderstorms and precipitation.
The latter is most common. It is with this type that weather radar is most
helpful to the pilot. It is not possible to detect clear air turbulence with
this type of radar system. Weather guidance is now available from
ground radar stations in some areas. However, this system suffers in
comparison with the airborne weather radar where the weather is clearly
visible on the pilot’s indicator, instantly available for the pilot to act upon,
considering his immediate circumstances and future flight planning.
The strong up and down drafts in a thunderstorm create very large rain-
drops which are usually displayed on a radar as level 4.
The probability of turbulence in these strong vertical gusts is great. The
National Severe Storms Laboratory (NSSL) has found that the intensity
level of the precipitation reflection correlates with the degree of turbu-
lence found in a thunderstorm. The most severe turbulence in the
storm, however, may not be at the same place that gives the greatest
radar reflectivity.
The rate of change in rainfall rate laterally within a storm is called the rain
gradient. This change will appear on the indicator as a change from
green to yellow to red to magenta. If the rainfall rate increases from level
1 to 4 in a short distance, the rain gradient is steep and severe turbu-
lence is often present. Avoid any storm with a steep rain gradient by an
extra margin and especially avoid flying near the portion of the storm with
the steepest gradient.
TORNADOES
It is possible that conclusive methods of detecting tornadoes with air-
borne radar may eventually be developed. However, evidence collected
to date indicates tornadoes may be present if the following echoes are
observed:
A hook-shaped pendant which may be 5 or more miles long and in the
general shape of the numeral 6 strongly suggests the presence of a
major tornado, especially if the pendant is bright and if it projects from
the southwest quadrant (northeast quadrant in the southern hemisphere)
of a major thunderstorm moving eastward. The pendant may be masked
by ground clutter when viewed on the indicator and in some cases might
Weather Mapping and Interpretation
RDR 2100 PG 3/12/07 3:45 PM Page 20