Target - Honeywell PRIMUS 660 Pilot's Manual

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.
LEVEL 1
GREEN
LIGHT
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Probability of Turbulence Presence
A28–1146–111
REV 2
PRIMUS
LEVEL 2
YELLOW
(4 mm / Hr) (12 mm / Hr)
RAINFALL RATE
in a Weather Target
Figure 5–32
R
660 Digital Weather Radar System
LEVEL 3
RED
(50 mm / Hr)
LEVEL 4
MAGENTA
AD–15357–R3@
Radar Facts
5-35