PRIMUS
R
660 Digital Weather Radar System
A28–1146–111
REV 2 5-35
Radar Facts
Although penetrating a storm with a red (level three) core appears to be
an acceptable risk, it is not. At the lower end of the red zone, there is
no chance of extreme turbulence, a slight chance of severe turbulence,
and a 40% chance of moderate turbulence. However, the radar lumps
all of the rainfall rates between 12 mm to 50 mm per hour into one group
– a level three (red). Once the rainfall rate reaches the red threshold,
it masks any additional information about the rainfall rate until the
magenta threshold is reached. A red return covers a range of
turbulence probabilities and the worst case must be assumed,
especially since extreme, destructive turbulence is born in the red zone.
Therefore, once the red threshold is reached, the risk in penetration
becomes totally unacceptable.
Likewise, once the magenta threshold is reached, it must be
assumed that more severe weather is being masked.
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
TURBULENCE PROBABILITY
LIGHT
LEVEL 1
GREEN
LEVEL 2
YELLOW
LEVEL 3
RED
LEVEL 4
MAGENTA
(4 mm / Hr) (12 mm / Hr) (50 mm / Hr)
AD–15357–R3@
RAINFALL RATE
Probability of Turbulence Presence
in a Weather Target
Figure 5–32
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