Figure 3-14.-Visual, local noon, third day.
1. Select two to four points along the front where a
regular and reliable pressure gradient exists, and
determine the geostrophic wind by use of the
geostrophic wind scale. (NOTE: Do not use the
observed wind.) The wind speed should be determined
a short distance behind a cold front and a short
distance ahead of the warm front where a
representative gradient can be found. The points on
the isobars in figure 3-16 serve as a guide to the proper
selection of the geostrophic wind measurements.
2. Draw a vector toward the front, parallel to the
isobars from where the geostrophic wind was
determined. The vectors labeled y in figure 3-16
illustrate this step.
3. Draw a vector perpendicular to the front
originating at the point where the y vector intersects
the front, and label this vector x, as illustrated in
4. At a convenient distance from the intersection,
along the x vector, construct a perpendicular to the