Measure the angle formed by the radial lines drawn from ground zero to

the cloud-top height and two-thirds stem height points on the fallout

vector plot (or the radial lines which have been expanded to include

vectors between the two-thirds stem height and the cloud-top height). If

the angle formed is less than 40 degrees, bisect the angle and expand the

angle formed by the two radial lines to 40 degrees, 20 degrees on each

side of the bisector, (Figure 4-3).

Measure the azimuths, in mils or degrees from grid north, of the final

left and right radial lines and record on lines p and q of the worksheet

(use four digits).

Figure 4-4 on page 4-8 is a completed detailed

fallout prediction worksheet.

Start with GZ on an overlay at the selected map scale, and extend the

radial lines at their proper azimuths to any convenient distance. Mark

grid north on this overlay. (The fallout wind vector plot was originally

drawn to a convenient map scale; for example, 1:500,000. If it is more

convenient, a different map scale can now be used to complete the fallout

prediction.)

Between the two radial lines drawn from ground zero, using ground zero as

center, draw two arcs with radii equal to the Zone I and Zone II downwind

distances.

Using ground zero as center, draw a circle around ground zero with a

radius equal to the cloud radius at the selected map scale.

Draw two tangents extending from the ground zero circle to the points of

intersection of the two radial lines with the Zone I arc.

Using ground zero as center, indicate the estimated times of arrival of

fallout by drawing dashed arcs downwind at distances equal to the product

of the effective wind speed and each hour of interest.

A completed

detailed fallout prediction plot is shown at Figure 4-5 on page 4-9.