towards which the wind is blowing) in true degrees,
while the FFF is the effective-downwind speed in
kilometers per hour. The a is the expansion angle
indicator, which is encoded as a "/" if only the 40°
standard angle is to be used. Expansion angle indicators
are provided in table 5-2. Predictions for several areas
may be contained in a single message.
Table 5-2.—Expansion Angle Indicators
INDICATOR
EXPANSION ANGLE
/
5
6
7
8
9
0
1
2
3
40°
50°
60°
70°
80°
90°
100°
110°
120°
greater than 120°
CIRCLE AROUND GZ
(wind speed less than 5
knots)
For a naval effective downwind forecast message
(NAV EDM), the units used are slightly different. The
area of validity, instead of being given as a UTM grid
square, is provided as 5° latitude and longitude squares
centered on the intersections of the latitude/longitude
lines. For example, 2800N 09500W represents a 5°
square centered at 28° 00’N 095° 00’W. Directions are
in true degrees, but all downwind distances are in
nautical miles.
Additionally, the format may be different,
depending on the organization producing the forecast.
The yield groups Alpha through Golf may be listed in a
vertical column instead of a horizontal row, as shown in
figure 5-2. The first three digits are the effective
downwind direction, while the last three digits are the
effective downwind speed. The number in parenthesis
is the expansion angle. In both ground force and naval
force EDFs or EDMs, when the effective downwind
speed is less than 8 KPH (5 knots), the radius of a
circular fallout pattern is given by the first three digits,
which are followed by three dashes.
Most of the effective downwind forecasts you will
actually use are produced on site by the Tactical
Environmental Support System (TESS). TESS
calculates fallout patterns based on a specific weapon
yield and input from a specified radiosonde data set. In
addition to a dosage rate plot, TESS provides both
English and Metric data similar to the NATO standard,
DFXX KNWC 111415Z
24HR NAVAL EFFECTIVE DOWNWIND FORECAST VALID 121200Z NOV 96
ZULU 111200Z
3000N 12500W
3000N
12000W
3000N 11500W
ALPHA
130008
125008
005---
BRAVO
135010
130008
007---
CHARLIE
145015(060)
140012
135009
DELTA
155020(060)
150018(050)
145015
ECHO
160022(060)
155021(060)
150018
FOXTROT
180025(070)
175026(070)
170023(060)
GOLF
180030(070)
180029(070)
180026(060)
Each line element is composed as follows:
FOXTROT
180
yield group
downwind direction
025
downwind speed
(070)
expansion angle
Figure 5-2.—Typical Naval Effective Downwind Message (NAV EDM).
5-3
